[1/2] iio: magnetometer: Add DT support for PNI RM3100

PNI RM3100 is a high resolution, large signal immunity magnetometer,
composed of 3 single sensors and a processing chip with MagI2C Interface.
PNI is not in the vendors' list, so this patch is also adding it.

Signed-off-by: Song Qiang <songqiang1304521@gmail.com>
---
Changes in v2:
        - Remove bus specific part in compatible string.

 .../bindings/iio/magnetometer/pni,rm3100.txt  | 20 +++++++++++++++++++
 .../devicetree/bindings/vendor-prefixes.txt   |  1 +
 2 files changed, 21 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/magnetometer/pni,rm3100.txt

On Tue, 25 Sep 2018 11:17:23 +0800
Song Qiang <songqiang1304521@gmail.com> wrote:

> PNI RM3100 is a high resolution, large signal immunity magnetometer,
> composed of 3 single sensors and a processing chip with MagI2C Interface.
> PNI is not in the vendors' list, so this patch is also adding it.
> 
> Signed-off-by: Song Qiang <songqiang1304521@gmail.com>
Hi Song,

Please clearly mark the title of the patch with V2.
[PATCH 1/2 V2] ...

(or I'm also happy with a cover letter that does the same though other
maintainers ask for every patch to be marked v2).

This makes it easy to quickly short the versions and check we are
looking at the latest.
> ---
> Changes in v2:
>         - Remove bus specific part in compatible string.
> 
>  .../bindings/iio/magnetometer/pni,rm3100.txt  | 20 +++++++++++++++++++
>  .../devicetree/bindings/vendor-prefixes.txt   |  1 +
>  2 files changed, 21 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/iio/magnetometer/pni,rm3100.txt
> 
> diff --git a/Documentation/devicetree/bindings/iio/magnetometer/pni,rm3100.txt b/Documentation/devicetree/bindings/iio/magnetometer/pni,rm3100.txt
> new file mode 100644
> index 000000000000..4677690fc5d0
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/magnetometer/pni,rm3100.txt
> @@ -0,0 +1,20 @@
> +* PNI RM3100 3-axis magnetometer sensor
> +
> +Required properties:
> +
> +- compatible : should be "pni,rm3100"
> +- reg : the I2C address or SPI chip select number of the sensor.
> +
> +Optional properties:
> +
> +- interrupts: data ready (DRDY) from the chip.
> +  The interrupts can be triggered on rising edges.
> +
> +Example:
> +
> +rm3100: rm3100@20 {
> +	compatible = "pni,rm3100";
> +	reg = <0x20>;
> +	interrupt-parent = <&gpio0>;
> +	interrupts = <4 IRQ_TYPE_EDGE_RISING>;
> +};
> diff --git a/Documentation/devicetree/bindings/vendor-prefixes.txt b/Documentation/devicetree/bindings/vendor-prefixes.txt
> index 41f0b97eb933..5bf3395fe9ae 100644
> --- a/Documentation/devicetree/bindings/vendor-prefixes.txt
> +++ b/Documentation/devicetree/bindings/vendor-prefixes.txt
> @@ -288,6 +288,7 @@ pine64	Pine64
>  pixcir  PIXCIR MICROELECTRONICS Co., Ltd
>  plathome	Plat'Home Co., Ltd.
>  plda	PLDA
> +pni     PNI

A quick scan around their website suggests they are actually
"PNI Sensor Corporation"
I'm not sure how fussy we are on naming in here but probable best to be as specific
as possible.

>  portwell	Portwell Inc.
>  poslab	Poslab Technology Co., Ltd.
>  powervr	PowerVR (deprecated, use img)

On Tue, 25 Sep 2018 11:17:24 +0800
Song Qiang <songqiang1304521@gmail.com> wrote:

> PNI RM3100 is a high resolution, large signal immunity magnetometer,
> composed of 3 single sensors and a processing chip with MagI2C Interface.
> 
> Following functions are available:
> - Single-shot measurement from
>   /sys/bus/iio/devices/iio:deviceX/in_magn_{axis}_raw
> - Triggerd buffer measurement.
> - Both i2c and spi interface are supported.
> - Both interrupt and polling measurement is supported, depands on if
>   the 'interrupts' in DT is declared.
> 
> Signed-off-by: Song Qiang <songqiang1304521@gmail.com>
Various minor comments inline.  Definitely heading in the right direction.

Good work.

Thanks,

Jonathan

> ---
> Changes in v2:
> 	- Add scale channel.
> 	- Add EXPORT_SYMBOL_GPL() to export regmap confuguration
> 	  structures.
> 	- Add sampling frequency available attribute.
> 	- Clean up headers and License declarations.
> 	- Change axis number to 3.
> 	- Remove bus specific part in compatible string.
> 	- Remove le32_to_cpu().
> 	- Check cycle count registers at *_probe().
> 	- Format comments.
> 	- Spell check.
> 	- Change prefix from RM_* to RM3100_*.
> 	- Check all error return paths.
> 	- Add devm_add_action() to avoid race condition when remove.
> 
>  MAINTAINERS                            |   7 +
>  drivers/iio/magnetometer/Kconfig       |  29 ++
>  drivers/iio/magnetometer/Makefile      |   4 +
>  drivers/iio/magnetometer/rm3100-core.c | 470 +++++++++++++++++++++++++
>  drivers/iio/magnetometer/rm3100-i2c.c  |  58 +++
>  drivers/iio/magnetometer/rm3100-spi.c  |  64 ++++
>  drivers/iio/magnetometer/rm3100.h      |  73 ++++
>  7 files changed, 705 insertions(+)
>  create mode 100644 drivers/iio/magnetometer/rm3100-core.c
>  create mode 100644 drivers/iio/magnetometer/rm3100-i2c.c
>  create mode 100644 drivers/iio/magnetometer/rm3100-spi.c
>  create mode 100644 drivers/iio/magnetometer/rm3100.h
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 967ce8cdd1cc..14eeeb072403 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -11393,6 +11393,13 @@ M:	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
>  S:	Maintained
>  F:	drivers/pnp/
>  
> +PNI RM3100 IIO DRIVER
> +M:	Song Qiang <songqiang1304521@gmail.com>
> +L:	linux-iio@vger.kernel.org
> +S:	Maintained
> +F:	drivers/iio/magnetometer/rm3100*
> +F:	Documentation/devicetree/bindings/iio/magnetometer/pni,rm3100.txt
> +
>  POSIX CLOCKS and TIMERS
>  M:	Thomas Gleixner <tglx@linutronix.de>
>  L:	linux-kernel@vger.kernel.org
> diff --git a/drivers/iio/magnetometer/Kconfig b/drivers/iio/magnetometer/Kconfig
> index ed9d776d01af..f130b866a4fc 100644
> --- a/drivers/iio/magnetometer/Kconfig
> +++ b/drivers/iio/magnetometer/Kconfig
> @@ -175,4 +175,33 @@ config SENSORS_HMC5843_SPI
>  	  - hmc5843_core (core functions)
>  	  - hmc5843_spi (support for HMC5983)
>  
> +config SENSORS_RM3100
> +	tristate
> +	select IIO_BUFFER
> +	select IIO_TRIGGERED_BUFFER
> +
> +config SENSORS_RM3100_I2C
> +	tristate "PNI RM3100 9-Axis Magnetometer (I2C)"
> +	depends on I2C
> +	select SENSORS_RM3100
> +	select REGMAP_I2C
> +	help
> +	  Say Y here to add support for the PNI RM3100 9-Axis Magnetometer.

Still doesn't have 9 axes ;)

> +
> +	  This driver can also be compiled as a module.
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called rm3100-i2c.
> +
> +config SENSORS_RM3100_SPI
> +	tristate "PNI RM3100 9-Axis Magnetometer (SPI)"
> +	depends on SPI_MASTER
> +	select SENSORS_RM3100
> +	select REGMAP_SPI
> +	help
> +	  Say Y here to add support for the PNI RM3100 9-Axis Magnetometer.
> +
> +	  This driver can also be compiled as a module.
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called rm3100-spi.
> +
>  endmenu
> diff --git a/drivers/iio/magnetometer/Makefile b/drivers/iio/magnetometer/Makefile
> index 664b2f866472..ba1bc34b82fa 100644
> --- a/drivers/iio/magnetometer/Makefile
> +++ b/drivers/iio/magnetometer/Makefile
> @@ -24,3 +24,7 @@ obj-$(CONFIG_IIO_ST_MAGN_SPI_3AXIS) += st_magn_spi.o
>  obj-$(CONFIG_SENSORS_HMC5843)		+= hmc5843_core.o
>  obj-$(CONFIG_SENSORS_HMC5843_I2C)	+= hmc5843_i2c.o
>  obj-$(CONFIG_SENSORS_HMC5843_SPI)	+= hmc5843_spi.o
> +
> +obj-$(CONFIG_SENSORS_RM3100)		+= rm3100-core.o
> +obj-$(CONFIG_SENSORS_RM3100_I2C)	+= rm3100-i2c.o
> +obj-$(CONFIG_SENSORS_RM3100_SPI)	+= rm3100-spi.o
> diff --git a/drivers/iio/magnetometer/rm3100-core.c b/drivers/iio/magnetometer/rm3100-core.c
> new file mode 100644
> index 000000000000..5d28b53b7a04
> --- /dev/null
> +++ b/drivers/iio/magnetometer/rm3100-core.c
> @@ -0,0 +1,470 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * PNI RM3100 3-axis geomagnetic sensor driver core.
> + *
> + * Copyright (C) 2018 Song Qiang <songqiang1304521@gmail.com>
> + *
> + * User Manual available at
> + * <https://www.pnicorp.com/download/rm3100-user-manual/>
> + *
> + * TODO: event generaton, pm.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/delay.h>
> +#include <linux/interrupt.h>
> +#include <linux/slab.h>

If there is no other reason for a particular order of header includes
alphabetical is always preferred.

> +
> +#include <linux/iio/iio.h>
> +#include <linux/iio/sysfs.h>
> +#include <linux/iio/triggered_buffer.h>
> +#include <linux/iio/trigger_consumer.h>
> +#include <linux/iio/buffer.h>
> +#include <linux/iio/kfifo_buf.h>
> +
> +#include "rm3100.h"
> +
> +static const struct regmap_range rm3100_readable_ranges[] = {
> +	regmap_reg_range(RM3100_W_REG_START, RM3100_W_REG_END),
> +};
> +
> +const struct regmap_access_table rm3100_readable_table = {
> +	.yes_ranges = rm3100_readable_ranges,
> +	.n_yes_ranges = ARRAY_SIZE(rm3100_readable_ranges),
> +};
> +EXPORT_SYMBOL_GPL(rm3100_readable_table);
> +
> +static const struct regmap_range rm3100_writable_ranges[] = {
> +	regmap_reg_range(RM3100_R_REG_START, RM3100_R_REG_END),
> +};
> +
> +const struct regmap_access_table rm3100_writable_table = {
> +	.yes_ranges = rm3100_writable_ranges,
> +	.n_yes_ranges = ARRAY_SIZE(rm3100_writable_ranges),
> +};
> +EXPORT_SYMBOL_GPL(rm3100_writable_table);
> +
> +static const struct regmap_range rm3100_volatile_ranges[] = {
> +	regmap_reg_range(RM3100_V_REG_START, RM3100_V_REG_END),
> +};
> +
> +const struct regmap_access_table rm3100_volatile_table = {
> +	.yes_ranges = rm3100_volatile_ranges,
> +	.n_yes_ranges = ARRAY_SIZE(rm3100_volatile_ranges),
> +};
> +EXPORT_SYMBOL_GPL(rm3100_volatile_table);
> +
> +static irqreturn_t rm3100_irq_handler(int irq, void *d)
> +{
> +	struct rm3100_data *data = d;
> +
> +	complete(&data->measuring_done);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static int rm3100_wait_measurement(struct rm3100_data *data)
> +{
> +	struct regmap *regmap = data->regmap;
> +	unsigned int val;
> +	int tries = 20;
> +	int ret;
> +
> +	/*
> +	 * A read cycle of 400kbits i2c; bus is about 20us, plus the time
> +	 * used for scheduling, a read cycle of fast mode of this device
> +	 * can reach 1.7ms, it may be possible for data to arrive just
> +	 * after we check the RM3100_REG_STATUS. In this case, irq_handler is
> +	 * called before measuring_done is reinitialized, it will wait
> +	 * forever for data that has already been ready.
> +	 * Reinitialize measuring_done before looking up makes sure we
> +	 * will always capture interrupt no matter when it happened.
> +	 */
> +	if (data->use_interrupt)
> +		reinit_completion(&data->measuring_done);
> +
> +	ret = regmap_read(regmap, RM3100_REG_STATUS, &val);
> +	if (ret < 0)
> +		return ret;
> +
> +	if ((val & RM3100_STATUS_DRDY) != RM3100_STATUS_DRDY) {
> +		if (data->use_interrupt) {
> +			ret = wait_for_completion_timeout(&data->measuring_done,
> +				msecs_to_jiffies(data->conversion_time));
> +			if (ret < 0)
> +				return -ETIMEDOUT;
> +		} else {
> +			do {
> +				usleep_range(1000, 5000);
> +
> +				ret = regmap_read(regmap, RM3100_REG_STATUS,
> +						  &val);
> +				if (ret < 0)
> +					return ret;
> +
> +				if (val & RM3100_STATUS_DRDY)
> +					break;
> +			} while (--tries);
> +			if (!tries)
> +				return -ETIMEDOUT;
> +		}
> +	}
> +	return 0;
> +}
> +
> +static int rm3100_read_mag(struct rm3100_data *data, int idx, int *val)
> +{
> +	struct regmap *regmap = data->regmap;
> +	u8 buffer[3];
> +	int ret;
> +
> +	mutex_lock(&data->lock);
> +	ret = rm3100_wait_measurement(data);
> +	if (ret < 0) {
> +		mutex_unlock(&data->lock);
> +		return ret;
> +	}
> +
> +	ret = regmap_bulk_read(regmap, RM3100_REG_MX2 + 3 * idx, buffer, 3);
> +	mutex_unlock(&data->lock);
> +	if (ret < 0)
> +		return ret;
> +
> +	*val = sign_extend32((buffer[0] << 16) | (buffer[1] << 8) | buffer[2],
> +			     23);
> +
> +	return IIO_VAL_INT;
> +}
> +
> +#define RM3100_CHANNEL(axis, idx)					\
> +	{								\
> +		.type = IIO_MAGN,					\
> +		.modified = 1,						\
> +		.channel2 = IIO_MOD_##axis,				\
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
> +		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) |	\
> +			BIT(IIO_CHAN_INFO_SAMP_FREQ),			\
> +		.scan_index = idx,					\
> +		.scan_type = {						\
> +			.sign = 's',					\
> +			.realbits = 24,					\
> +			.storagebits = 32,				\
> +			.shift = 8,					\
> +			.endianness = IIO_LE,				\
> +		},							\
> +	}
> +
> +static const struct iio_chan_spec rm3100_channels[] = {
> +	RM3100_CHANNEL(X, 0),
> +	RM3100_CHANNEL(Y, 1),
> +	RM3100_CHANNEL(Z, 2),
> +	IIO_CHAN_SOFT_TIMESTAMP(3),
> +};
> +
> +static const unsigned long rm3100_scan_masks[] = {GENMASK(2, 0), 0};

This is really three separate enables, so I'd put it long hand
as BIT(0) | BIT(1) | BIT(2) to make that apparent in the code.

> +
> +static IIO_CONST_ATTR_SAMP_FREQ_AVAIL(
> +	"600 300 150 75 37 18 9 4.5 2.3 1.2 0.6 0.3 0.015 0.075"
> +);
> +
> +static struct attribute *rm3100_attributes[] = {
> +	&iio_const_attr_sampling_frequency_available.dev_attr.attr,
> +	NULL,
> +};
> +
> +static const struct attribute_group rm3100_attribute_group = {
> +	.attrs = rm3100_attributes,
> +};
> +
> +#define RM3100_SAMP_NUM			14
> +
> +/*
> + * Frequency : rm3100_samp_rates[][0].rm3100_samp_rates[][1]Hz.
> + * Time between reading: rm3100_sam_rates[][2]ms.
> + * The first one is actually 1.7ms.
> + */
> +static const int rm3100_samp_rates[RM3100_SAMP_NUM][3] = {
> +	{600, 0, 2}, {300, 0, 3}, {150, 0, 7}, {75, 0, 13}, {37, 0, 27},
> +	{18, 0, 55}, {9, 0, 110}, {4, 500000, 220}, {2, 300000, 440},
> +	{1, 200000, 800}, {0, 600000, 1600}, {0, 300000, 3300},
> +	{0, 15000, 6700},  {0, 75000, 13000}
> +};
> +
> +static int rm3100_get_samp_freq(struct rm3100_data *data, int *val, int *val2)
> +{
> +	int ret;
> +	int tmp;
> +
> +	mutex_lock(&data->lock);
> +	ret = regmap_read(data->regmap, RM3100_REG_TMRC, &tmp);
> +	mutex_unlock(&data->lock);
> +	if (ret < 0)
> +		return ret;
> +	*val = rm3100_samp_rates[tmp - RM3100_TMRC_OFFSET][0];
> +	*val2 = rm3100_samp_rates[tmp - RM3100_TMRC_OFFSET][1];
> +
> +	return IIO_VAL_INT_PLUS_MICRO;
> +}
> +
> +static int rm3100_set_cycle_count(struct rm3100_data *data, int val)
> +{
> +	int ret;
> +	u8 i;
> +
> +	for (i = 0; i < 3; i++) {
> +		ret = regmap_write(data->regmap, RM3100_REG_CC_X + 2 * i, 100);

Does this write it to the same value irrespective of the value of val?
Seems odd.

> +		if (ret < 0)
> +			return ret;
> +	}
> +	if (val == 50)

Switch would be nicer.  Also why have all other values call back to
2 rather than generating an error?

> +		data->cycle_count_index = 0;
> +	else if (val == 100)
> +		data->cycle_count_index = 1;
> +	else
> +		data->cycle_count_index = 2;
> +
> +	return 0;
> +}
> +
> +static int rm3100_set_samp_freq(struct rm3100_data *data, int val, int val2)
> +{
> +	struct regmap *regmap = data->regmap;
> +	int cycle_count;
> +	int ret;
> +	int i;
> +
> +	mutex_lock(&data->lock);

Why are you taking this lock? It's not well documented what it protects
so it's not clear in this path why it is taken.
(hint add a comment to the definition of the lock to make it clear!)
- note I'm not saying it shouldn't be taken here, just that there is no
comment to justify it..

> +	/* All cycle count registers use the same value. */
> +	ret = regmap_read(regmap, RM3100_REG_CC_X, &cycle_count);
> +	if (ret < 0)
> +		goto unlock_return;
> +
> +	for (i = 0; i < RM3100_SAMP_NUM; i++) {
> +		if (val == rm3100_samp_rates[i][0] &&
> +		    val2 == rm3100_samp_rates[i][1])
> +			break;
> +	}
> +	if (i == RM3100_SAMP_NUM) {
> +		ret = -EINVAL;
> +		goto unlock_return;
> +	}
> +
> +	ret = regmap_write(regmap, RM3100_REG_TMRC, i + RM3100_TMRC_OFFSET);
> +	if (ret < 0)
> +		goto unlock_return;
> +
> +	/* Checking if cycle count registers need changing. */
> +	if (val == 600 && cycle_count == 200) {
> +		ret = rm3100_set_cycle_count(data, 100);
> +		if (ret < 0)
> +			goto unlock_return;
> +	} else if (val != 600 && cycle_count == 100) {
> +		ret = rm3100_set_cycle_count(data, 200);
> +		if (ret < 0)
> +			goto unlock_return;
> +	}
> +
> +	/* Writing TMRC registers requires CMM reset. */
> +	ret = regmap_write(regmap, RM3100_REG_CMM, 0);
> +	if (ret < 0)
> +		goto unlock_return;
> +	ret = regmap_write(regmap, RM3100_REG_CMM,
> +		RM3100_CMM_X | RM3100_CMM_Y | RM3100_CMM_Z | RM3100_CMM_START);
> +	mutex_unlock(&data->lock);

I would move this unlock until after setting the value below
(only slightly wider scope than the minimum)
then have a single exit point by moving the unlock_return label
above it and returning ret in all cases.

> +	if (ret < 0)
> +		return ret;
> +
> +	data->conversion_time = rm3100_samp_rates[i][2] + 3000;
> +	return 0;
> +
> +unlock_return:
> +	mutex_unlock(&data->lock);
> +	return ret;
> +}
> +
> +/*
> + * Scale of this sensor depends on cycle count value, these three values
> + * are corresponding to cycle count value 50, 100, 200.
> + * scale = output / gain * 10e4.
> + */
> +const static int rm3100_scale[] = {500, 263, 133};
> +
> +static int rm3100_read_raw(struct iio_dev *indio_dev,
> +			   const struct iio_chan_spec *chan,
> +			   int *val, int *val2, long mask)
> +{
> +	struct rm3100_data *data = iio_priv(indio_dev);
> +	int ret;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		ret = iio_device_claim_direct_mode(indio_dev);
> +		if (ret < 0) {
> +			iio_device_release_direct_mode(indio_dev);

Check what happens when claim_direct_mode fails.

You don't need to release it in this path.  Any kernel function
should handle it's own error paths (and this one definitely does)
so if you get an error you should never need to clean up after
the function that gave it.

> +			return ret;
> +		}
> +		ret = rm3100_read_mag(data, chan->scan_index, val);
> +		iio_device_release_direct_mode(indio_dev);
> +
> +		return ret;
> +	case IIO_CHAN_INFO_SCALE:
> +		*val = 0;
> +		*val2 = rm3100_scale[data->cycle_count_index];
> +
> +		return IIO_VAL_INT_PLUS_MICRO;
> +	case IIO_CHAN_INFO_SAMP_FREQ:
> +		return rm3100_get_samp_freq(data, val, val2);
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int rm3100_write_raw(struct iio_dev *indio_dev,
> +			    struct iio_chan_spec const *chan,
> +			    int val, int val2, long mask)
> +{
> +	struct rm3100_data *data = iio_priv(indio_dev);
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_SAMP_FREQ:
> +		return rm3100_set_samp_freq(data, val, val2);
> +	default:
> +		return -EINVAL;
> +	}
> +
> +}
> +
> +static const struct iio_info rm3100_info = {
> +	.attrs = &rm3100_attribute_group,
> +	.read_raw = rm3100_read_raw,
> +	.write_raw = rm3100_write_raw,
> +};
> +
> +static irqreturn_t rm3100_trigger_handler(int irq, void *p)
> +{
> +	struct iio_poll_func *pf = p;
> +	struct iio_dev *indio_dev = pf->indio_dev;
> +	struct rm3100_data *data = iio_priv(indio_dev);
> +	struct regmap *regmap = data->regmap;
> +	u8 buffer[9];
> +	int ret;
> +	int i;
> +
> +	mutex_lock(&data->lock);
> +	ret = rm3100_wait_measurement(data);
> +	if (ret < 0) {
> +		mutex_unlock(&data->lock);
> +		goto done;
> +	}
> +
> +	ret = regmap_bulk_read(regmap, RM3100_REG_MX2, buffer, sizeof(buffer));
> +	mutex_unlock(&data->lock);

data->lock is I assume to protect the buffer.  We are still using it
so you need to hold it longer...  In fact all the way to the
done label.  So just move your unlock down there for all paths.

> +	if (ret < 0)
> +		goto done;
> +
> +	/* Convert XXXYYYZZZxxx to XXXxYYYxZZZx. x for padding. */
> +	for (i = 0; i < 3; i++)
> +		memcpy(data->buffer + i * 4, buffer + i * 3, 3);

Firstly X doesn't need copying.
Secondly the copy of Y actually overwrites the value of Z
XXXYYYZZZxxx
XXXxYYYZZxxx
XXXxYYYxYZZx

I think...

> +
> +	iio_push_to_buffers_with_timestamp(indio_dev, data->buffer,
> +			iio_get_time_ns(indio_dev));

Align with opening bracket. 

> +
> +done:
> +	iio_trigger_notify_done(indio_dev->trig);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static void rm3100_remove(void *dh)
> +{
> +	struct rm3100_data *data = (struct rm3100_data *)dh;
> +	int ret;
> +
> +	ret = regmap_write(data->regmap, RM3100_REG_CMM, 0x00);
> +	if (ret < 0)
> +		dev_err(data->dev, "failed to stop device.\n");
> +}
> +
> +int rm3100_common_probe(struct device *dev, struct regmap *regmap, int irq)
> +{
> +	struct iio_dev *indio_dev;
> +	struct rm3100_data *data;
> +	int tmp;
> +	int ret;
> +
> +	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	data = iio_priv(indio_dev);
> +	data->dev = dev;
> +	data->regmap = regmap;
> +	data->buffer = devm_kzalloc(dev, RM3100_SCAN_BYTES, GFP_KERNEL);
> +	if (!data->buffer)
> +		return -ENOMEM;
> +
> +	mutex_init(&data->lock);
> +
> +	indio_dev->dev.parent = dev;
> +	indio_dev->name = "rm3100";
> +	indio_dev->info = &rm3100_info;
> +	indio_dev->channels = rm3100_channels;
> +	indio_dev->num_channels = ARRAY_SIZE(rm3100_channels);
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +	indio_dev->available_scan_masks = rm3100_scan_masks;
> +
> +	if (!irq)
> +		data->use_interrupt = false;
> +	else {
> +		data->use_interrupt = true;
> +		ret = devm_request_irq(dev,
> +				       irq,
> +				       rm3100_irq_handler,
> +				       IRQF_TRIGGER_RISING,
> +				       indio_dev->name,
> +				       data);
> +		if (ret < 0) {
> +			dev_err(dev, "request irq line failed.\n");
> +			return ret;
> +		}
> +		init_completion(&data->measuring_done);
> +	}
> +
> +	ret = devm_iio_triggered_buffer_setup(dev, indio_dev, NULL,
> +					      rm3100_trigger_handler, NULL);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* 3sec more wait time. */

I have no idea what this comment is referring to..
Not seeing any waiting here...

> +	ret = regmap_read(regmap, RM3100_REG_TMRC, &tmp);
> +	if (ret < 0)
> +		return ret;
> +	data->conversion_time =
> +		rm3100_samp_rates[tmp-RM3100_TMRC_OFFSET][2] + 3000;

spacing around -  
Please check this throughout.

> +
> +	/* Cycle count values may not be what we want. */
> +	ret = regmap_read(data->regmap, RM3100_REG_TMRC, &tmp);
> +	if (ret < 0)
> +		return ret;
> +	if ((tmp - RM3100_TMRC_OFFSET) == 0)
> +		rm3100_set_cycle_count(data, 100);
> +	else
> +		rm3100_set_cycle_count(data, 200);
> +
> +	/* Starting all channels' conversion. */
> +	ret = regmap_write(regmap, RM3100_REG_CMM,
> +		RM3100_CMM_X | RM3100_CMM_Y | RM3100_CMM_Z | RM3100_CMM_START);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = devm_iio_device_register(dev, indio_dev);
> +	if (ret < 0)
> +		return ret;
> +
> +	return devm_add_action(dev, rm3100_remove, data);

This is in the wrong order.  If you were to get an error
from devm_iio_device_register you would not unwind the stuff
in remove.

Note however there is a nasty corner in that devm_add_action can
fail. If that fails, you need to manually call your unwind function
before returning.


> +}
> +EXPORT_SYMBOL_GPL(rm3100_common_probe);
> +
> +MODULE_AUTHOR("Song Qiang <songqiang1304521@gmail.com>");
> +MODULE_DESCRIPTION("PNI RM3100 3-axis magnetometer i2c driver");
> +MODULE_LICENSE("GPL v2");
> diff --git a/drivers/iio/magnetometer/rm3100-i2c.c b/drivers/iio/magnetometer/rm3100-i2c.c
> new file mode 100644
> index 000000000000..e8b84fac771b
> --- /dev/null
> +++ b/drivers/iio/magnetometer/rm3100-i2c.c
> @@ -0,0 +1,58 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Support for PNI RM3100 3-axis geomagnetic sensor a i2c bus.
> + *
> + * Copyright (C) 2018 Song Qiang <songqiang1304521@gmail.com>
> + *
> + * i2c slave address 0x20 + SA1 << 1 + SA0.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/i2c.h>
> +
> +#include "rm3100.h"
> +
> +static const struct regmap_config rm3100_regmap_config = {
> +	.reg_bits = 8,
> +	.val_bits = 8,
> +
> +	.rd_table = &rm3100_readable_table,
> +	.wr_table = &rm3100_writable_table,
> +	.volatile_table = &rm3100_volatile_table,
> +
> +	.cache_type = REGCACHE_RBTREE,
> +};
> +
> +static int rm3100_probe(struct i2c_client *client)
> +{
> +	struct regmap *regmap;
> +
> +	if (!i2c_check_functionality(client->adapter,
> +		I2C_FUNC_SMBUS_READ_I2C_BLOCK | I2C_FUNC_SMBUS_BYTE_DATA))
> +		return -EOPNOTSUPP;
> +
> +	regmap =  devm_regmap_init_i2c(client, &rm3100_regmap_config);
> +	if (IS_ERR(regmap))
> +		return PTR_ERR(regmap);
> +
> +	return rm3100_common_probe(&client->dev, regmap, client->irq);
> +}
> +
> +static const struct of_device_id rm3100_dt_match[] = {
> +	{ .compatible = "pni,rm3100", },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(of, rm3100_dt_match);
> +
> +static struct i2c_driver rm3100_driver = {
> +	.driver = {
> +		.name = "rm3100-i2c",
> +		.of_match_table = rm3100_dt_match,
> +	},
> +	.probe_new = rm3100_probe,
> +};
> +module_i2c_driver(rm3100_driver);
> +
> +MODULE_AUTHOR("Song Qiang <songqiang1304521@gmail.com>");
> +MODULE_DESCRIPTION("PNI RM3100 3-axis magnetometer i2c driver");
> +MODULE_LICENSE("GPL v2");
> diff --git a/drivers/iio/magnetometer/rm3100-spi.c b/drivers/iio/magnetometer/rm3100-spi.c
> new file mode 100644
> index 000000000000..1a7a69fb9872
> --- /dev/null
> +++ b/drivers/iio/magnetometer/rm3100-spi.c
> @@ -0,0 +1,64 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Support for PNI RM3100 3-axis geomagnetic sensor a spi bus.
> + *
> + * Copyright (C) 2018 Song Qiang <songqiang1304521@gmail.com>
> + */
> +
> +#include <linux/module.h>
> +#include <linux/spi/spi.h>
> +
> +#include "rm3100.h"
> +
> +static const struct regmap_config rm3100_regmap_config = {
> +	.reg_bits = 8,
> +	.val_bits = 8,
> +
> +	.rd_table = &rm3100_readable_table,
> +	.wr_table = &rm3100_writable_table,
> +	.volatile_table = &rm3100_volatile_table,
> +
> +	.read_flag_mask = 0x80,
> +
> +	.cache_type = REGCACHE_RBTREE,
> +};
> +
> +static int rm3100_probe(struct spi_device *spi)
> +{
> +	struct regmap *regmap;
> +	int ret;
> +
> +	/* Actually this device supports both mode 0 and mode 3. */
> +	spi->mode = SPI_MODE_0;
> +	/* Data rates cannot exceed 1Mbits. */
> +	spi->max_speed_hz = 1000000;
> +	spi->bits_per_word = 8;
> +	ret = spi_setup(spi);
> +	if (ret)
> +		return ret;
> +
> +	regmap =  devm_regmap_init_spi(spi, &rm3100_regmap_config);
> +	if (IS_ERR(regmap))
> +		return PTR_ERR(regmap);
> +
> +	return rm3100_common_probe(&spi->dev, regmap, spi->irq);
> +}
> +
> +static const struct of_device_id rm3100_dt_match[] = {
> +	{ .compatible = "pni,rm3100", },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(of, rm3100_dt_match);
> +
> +static struct spi_driver rm3100_driver = {
> +	.driver = {
> +		.name = "rm3100-spi",
> +		.of_match_table = rm3100_dt_match,
> +	},
> +	.probe = rm3100_probe,
> +};
> +module_spi_driver(rm3100_driver);
> +
> +MODULE_AUTHOR("Song Qiang <songqiang1304521@gmail.com>");
> +MODULE_DESCRIPTION("PNI RM3100 3-axis magnetometer spi driver");
> +MODULE_LICENSE("GPL v2");
> diff --git a/drivers/iio/magnetometer/rm3100.h b/drivers/iio/magnetometer/rm3100.h
> new file mode 100644
> index 000000000000..673647574add
> --- /dev/null
> +++ b/drivers/iio/magnetometer/rm3100.h
> @@ -0,0 +1,73 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Header file for PNI RM3100 driver
> + *
> + * Copyright (C) 2018 Song Qiang <songqiang1304521@gmail.com>
> + */
> +
> +#ifndef RM3100_CORE_H
> +#define RM3100_CORE_H
> +
> +#include <linux/regmap.h>
> +

Superficially it seems unlikely that any of the REG definitions
will ever be accessed from anywhere other than the -core.c file.

So it would be good to move them there.

General principle in the kernel is to limit the scope of anything
to the relevant files if possible.

> +#define RM3100_REG_REV_ID		0x36
> +
> +/* Cycle Count Registers. */
> +#define RM3100_REG_CC_X			0x05
> +#define RM3100_REG_CC_Y			0x07
> +#define RM3100_REG_CC_Z			0x09
> +
> +/* Continues Measurement Mode register. */
> +#define RM3100_REG_CMM			0x01
> +#define RM3100_CMM_START		BIT(0)
> +#define RM3100_CMM_X			BIT(4)
> +#define RM3100_CMM_Y			BIT(5)
> +#define RM3100_CMM_Z			BIT(6)
> +
> +/* TiMe Rate Configuration register. */
> +#define RM3100_REG_TMRC			0x0B
> +#define RM3100_TMRC_OFFSET		0x92
> +
> +/* Result Status register. */
> +#define RM3100_REG_STATUS		0x34
> +#define RM3100_STATUS_DRDY		BIT(7)
> +
> +/* Measurement result registers. */
> +#define RM3100_REG_MX2			0x24
> +#define RM3100_REG_MY2			0x27
> +#define RM3100_REG_MZ2			0x2a
> +
> +#define RM3100_W_REG_START		RM3100_REG_CMM
> +#define RM3100_W_REG_END		RM3100_REG_REV_ID
> +#define RM3100_R_REG_START		RM3100_REG_CMM
> +#define RM3100_R_REG_END		RM3100_REG_STATUS
> +#define RM3100_V_REG_START		RM3100_REG_MX2
> +#define RM3100_V_REG_END		RM3100_REG_STATUS
> +
> +#define RM3100_SCAN_BYTES		24
> +
> +struct rm3100_data {
> +	struct device *dev;
> +	struct regmap *regmap;
> +	struct completion measuring_done;
> +	bool use_interrupt;
> +
> +	int conversion_time;
> +	int cycle_count_index;
> +
> +	u8 *buffer;
> +
> +	/*
> +	 * To protect consistency of every measurement and sampling
> +	 * frequency change operations.
> +	 */
> +	struct mutex lock;
> +};
This doesn't seem to be used in the i2c and spi files either - so move
the definition to the top of the -core.c file.

> +
> +extern const struct regmap_access_table rm3100_readable_table;
> +extern const struct regmap_access_table rm3100_writable_table;
> +extern const struct regmap_access_table rm3100_volatile_table;
> +
> +int rm3100_common_probe(struct device *dev, struct regmap *regmap, int irq);
> +
> +#endif /* RM3100_CORE_H */

On 25/09/2018 9:30 PM, Jonathan Cameron wrote:
>> +static irqreturn_t rm3100_trigger_handler(int irq, void *p)
>> +{
>> +	struct iio_poll_func *pf = p;
>> +	struct iio_dev *indio_dev = pf->indio_dev;
>> +	struct rm3100_data *data = iio_priv(indio_dev);
>> +	struct regmap *regmap = data->regmap;
>> +	u8 buffer[9];
>> +	int ret;
>> +	int i;
>> +
>> +	mutex_lock(&data->lock);
>> +	ret = rm3100_wait_measurement(data);
>> +	if (ret < 0) {
>> +		mutex_unlock(&data->lock);
>> +		goto done;
>> +	}
>> +
>> +	ret = regmap_bulk_read(regmap, RM3100_REG_MX2, buffer, sizeof(buffer));
>> +	mutex_unlock(&data->lock);
>> +	if (ret < 0)
>> +		goto done;
>> +
>> +	/* Convert XXXYYYZZZxxx to XXXxYYYxZZZx. x for padding. */
>> +	for (i = 0; i < 3; i++)
>> +		memcpy(data->buffer + i * 4, buffer + i * 3, 3);
> Firstly X doesn't need copying.
> Secondly the copy of Y actually overwrites the value of Z
> XXXYYYZZZxxx
> XXXxYYYZZxxx
> XXXxYYYxYZZx
> 
> I think...
> 
>> +
>> +	iio_push_to_buffers_with_timestamp(indio_dev, data->buffer,
>> +			iio_get_time_ns(indio_dev));

memcpy target is a different buffer so should be ok.

But that raises the question of does it need to be?
'buffer' could be 12 bytes long and just shuffle Z then Y.
Do the unused bytes need to be zeroed? or does libiio mask them anyway?

On Tue, Sep 25, 2018 at 11:17:24AM +0800, Song Qiang wrote:
> PNI RM3100 is a high resolution, large signal immunity magnetometer,
> composed of 3 single sensors and a processing chip with MagI2C Interface.
> 
> Following functions are available:
> - Single-shot measurement from
>   /sys/bus/iio/devices/iio:deviceX/in_magn_{axis}_raw
> - Triggerd buffer measurement.
> - Both i2c and spi interface are supported.
> - Both interrupt and polling measurement is supported, depands on if
							 depends

>   the 'interrupts' in DT is declared.
> 
> Signed-off-by: Song Qiang <songqiang1304521@gmail.com>
> ---
> Changes in v2:
> 	- Add scale channel.
> 	- Add EXPORT_SYMBOL_GPL() to export regmap confuguration
> 	  structures.
> 	- Add sampling frequency available attribute.
> 	- Clean up headers and License declarations.
> 	- Change axis number to 3.
> 	- Remove bus specific part in compatible string.
> 	- Remove le32_to_cpu().
> 	- Check cycle count registers at *_probe().
> 	- Format comments.
> 	- Spell check.
> 	- Change prefix from RM_* to RM3100_*.
> 	- Check all error return paths.
> 	- Add devm_add_action() to avoid race condition when remove.
> 
>  MAINTAINERS                            |   7 +
>  drivers/iio/magnetometer/Kconfig       |  29 ++
>  drivers/iio/magnetometer/Makefile      |   4 +
>  drivers/iio/magnetometer/rm3100-core.c | 470 +++++++++++++++++++++++++
>  drivers/iio/magnetometer/rm3100-i2c.c  |  58 +++
>  drivers/iio/magnetometer/rm3100-spi.c  |  64 ++++
>  drivers/iio/magnetometer/rm3100.h      |  73 ++++
>  7 files changed, 705 insertions(+)
>  create mode 100644 drivers/iio/magnetometer/rm3100-core.c
>  create mode 100644 drivers/iio/magnetometer/rm3100-i2c.c
>  create mode 100644 drivers/iio/magnetometer/rm3100-spi.c
>  create mode 100644 drivers/iio/magnetometer/rm3100.h
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 967ce8cdd1cc..14eeeb072403 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -11393,6 +11393,13 @@ M:	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
>  S:	Maintained
>  F:	drivers/pnp/
>  
> +PNI RM3100 IIO DRIVER
> +M:	Song Qiang <songqiang1304521@gmail.com>
> +L:	linux-iio@vger.kernel.org
> +S:	Maintained
> +F:	drivers/iio/magnetometer/rm3100*
> +F:	Documentation/devicetree/bindings/iio/magnetometer/pni,rm3100.txt
> +
>  POSIX CLOCKS and TIMERS
>  M:	Thomas Gleixner <tglx@linutronix.de>
>  L:	linux-kernel@vger.kernel.org
> diff --git a/drivers/iio/magnetometer/Kconfig b/drivers/iio/magnetometer/Kconfig
> index ed9d776d01af..f130b866a4fc 100644
> --- a/drivers/iio/magnetometer/Kconfig
> +++ b/drivers/iio/magnetometer/Kconfig
> @@ -175,4 +175,33 @@ config SENSORS_HMC5843_SPI
>  	  - hmc5843_core (core functions)
>  	  - hmc5843_spi (support for HMC5983)
>  
> +config SENSORS_RM3100
> +	tristate
> +	select IIO_BUFFER
> +	select IIO_TRIGGERED_BUFFER
> +
> +config SENSORS_RM3100_I2C
> +	tristate "PNI RM3100 9-Axis Magnetometer (I2C)"
> +	depends on I2C
> +	select SENSORS_RM3100
> +	select REGMAP_I2C
> +	help
> +	  Say Y here to add support for the PNI RM3100 9-Axis Magnetometer.
> +
> +	  This driver can also be compiled as a module.
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called rm3100-i2c.
> +
> +config SENSORS_RM3100_SPI
> +	tristate "PNI RM3100 9-Axis Magnetometer (SPI)"
> +	depends on SPI_MASTER
> +	select SENSORS_RM3100
> +	select REGMAP_SPI
> +	help
> +	  Say Y here to add support for the PNI RM3100 9-Axis Magnetometer.
> +
> +	  This driver can also be compiled as a module.
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called rm3100-spi.

Look at drivers/iio/chemical/Kconfig and do it similarly as done for
BME680.

>  endmenu
> diff --git a/drivers/iio/magnetometer/Makefile b/drivers/iio/magnetometer/Makefile
> index 664b2f866472..ba1bc34b82fa 100644
> --- a/drivers/iio/magnetometer/Makefile
> +++ b/drivers/iio/magnetometer/Makefile
> @@ -24,3 +24,7 @@ obj-$(CONFIG_IIO_ST_MAGN_SPI_3AXIS) += st_magn_spi.o
>  obj-$(CONFIG_SENSORS_HMC5843)		+= hmc5843_core.o
>  obj-$(CONFIG_SENSORS_HMC5843_I2C)	+= hmc5843_i2c.o
>  obj-$(CONFIG_SENSORS_HMC5843_SPI)	+= hmc5843_spi.o
> +
> +obj-$(CONFIG_SENSORS_RM3100)		+= rm3100-core.o
> +obj-$(CONFIG_SENSORS_RM3100_I2C)	+= rm3100-i2c.o
> +obj-$(CONFIG_SENSORS_RM3100_SPI)	+= rm3100-spi.o
> diff --git a/drivers/iio/magnetometer/rm3100-core.c b/drivers/iio/magnetometer/rm3100-core.c
> new file mode 100644
> index 000000000000..5d28b53b7a04
> --- /dev/null
> +++ b/drivers/iio/magnetometer/rm3100-core.c
> @@ -0,0 +1,470 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * PNI RM3100 3-axis geomagnetic sensor driver core.
> + *
> + * Copyright (C) 2018 Song Qiang <songqiang1304521@gmail.com>
> + *
> + * User Manual available at
> + * <https://www.pnicorp.com/download/rm3100-user-manual/>
> + *
> + * TODO: event generaton, pm.
		  generation


> +#include <linux/module.h>
> +#include <linux/delay.h>
> +#include <linux/interrupt.h>
> +#include <linux/slab.h>
> +
> +#include <linux/iio/iio.h>
> +#include <linux/iio/sysfs.h>
> +#include <linux/iio/triggered_buffer.h>
> +#include <linux/iio/trigger_consumer.h>
> +#include <linux/iio/buffer.h>
> +#include <linux/iio/kfifo_buf.h>
> +
> +#include "rm3100.h"
> +
> +static const struct regmap_range rm3100_readable_ranges[] = {
> +	regmap_reg_range(RM3100_W_REG_START, RM3100_W_REG_END),
> +};
> +
> +const struct regmap_access_table rm3100_readable_table = {
> +	.yes_ranges = rm3100_readable_ranges,
> +	.n_yes_ranges = ARRAY_SIZE(rm3100_readable_ranges),
> +};
> +EXPORT_SYMBOL_GPL(rm3100_readable_table);
> +
> +static const struct regmap_range rm3100_writable_ranges[] = {
> +	regmap_reg_range(RM3100_R_REG_START, RM3100_R_REG_END),
> +};
> +
> +const struct regmap_access_table rm3100_writable_table = {
> +	.yes_ranges = rm3100_writable_ranges,
> +	.n_yes_ranges = ARRAY_SIZE(rm3100_writable_ranges),
> +};
> +EXPORT_SYMBOL_GPL(rm3100_writable_table);
> +
> +static const struct regmap_range rm3100_volatile_ranges[] = {
> +	regmap_reg_range(RM3100_V_REG_START, RM3100_V_REG_END),
> +};
> +
> +const struct regmap_access_table rm3100_volatile_table = {
> +	.yes_ranges = rm3100_volatile_ranges,
> +	.n_yes_ranges = ARRAY_SIZE(rm3100_volatile_ranges),
> +};
> +EXPORT_SYMBOL_GPL(rm3100_volatile_table);
> +
> +static irqreturn_t rm3100_irq_handler(int irq, void *d)
> +{
> +	struct rm3100_data *data = d;
> +
> +	complete(&data->measuring_done);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static int rm3100_wait_measurement(struct rm3100_data *data)
> +{
> +	struct regmap *regmap = data->regmap;
> +	unsigned int val;
> +	int tries = 20;
> +	int ret;
> +
> +	/*
> +	 * A read cycle of 400kbits i2c; bus is about 20us, plus the time
				      ; was mistakenly added ?

> +	 * used for scheduling, a read cycle of fast mode of this device
> +	 * can reach 1.7ms, it may be possible for data to arrive just
> +	 * after we check the RM3100_REG_STATUS. In this case, irq_handler is
> +	 * called before measuring_done is reinitialized, it will wait
> +	 * forever for data that has already been ready.
> +	 * Reinitialize measuring_done before looking up makes sure we
> +	 * will always capture interrupt no matter when it happened.
> +	 */
> +	if (data->use_interrupt)
> +		reinit_completion(&data->measuring_done);
> +
> +	ret = regmap_read(regmap, RM3100_REG_STATUS, &val);
> +	if (ret < 0)
> +		return ret;
> +
> +	if ((val & RM3100_STATUS_DRDY) != RM3100_STATUS_DRDY) {
> +		if (data->use_interrupt) {
> +			ret = wait_for_completion_timeout(&data->measuring_done,
> +				msecs_to_jiffies(data->conversion_time));
> +			if (ret < 0)
> +				return -ETIMEDOUT;
> +		} else {
> +			do {
> +				usleep_range(1000, 5000);
> +
> +				ret = regmap_read(regmap, RM3100_REG_STATUS,
> +						  &val);
> +				if (ret < 0)
> +					return ret;
> +
> +				if (val & RM3100_STATUS_DRDY)
> +					break;
> +			} while (--tries);
> +			if (!tries)
> +				return -ETIMEDOUT;
> +		}
> +	}
> +	return 0;
> +}
> +
> +static int rm3100_read_mag(struct rm3100_data *data, int idx, int *val)
> +{
> +	struct regmap *regmap = data->regmap;
> +	u8 buffer[3];
> +	int ret;
> +
> +	mutex_lock(&data->lock);
> +	ret = rm3100_wait_measurement(data);
> +	if (ret < 0) {
> +		mutex_unlock(&data->lock);
> +		return ret;
> +	}
> +
> +	ret = regmap_bulk_read(regmap, RM3100_REG_MX2 + 3 * idx, buffer, 3);
> +	mutex_unlock(&data->lock);
> +	if (ret < 0)
> +		return ret;
> +
> +	*val = sign_extend32((buffer[0] << 16) | (buffer[1] << 8) | buffer[2],
> +			     23);
> +
> +	return IIO_VAL_INT;
> +}
> +
> +#define RM3100_CHANNEL(axis, idx)					\
> +	{								\
> +		.type = IIO_MAGN,					\
> +		.modified = 1,						\
> +		.channel2 = IIO_MOD_##axis,				\
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
> +		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) |	\
> +			BIT(IIO_CHAN_INFO_SAMP_FREQ),			\
> +		.scan_index = idx,					\
> +		.scan_type = {						\
> +			.sign = 's',					\
> +			.realbits = 24,					\
> +			.storagebits = 32,				\
> +			.shift = 8,					\
> +			.endianness = IIO_LE,				\
> +		},							\
> +	}
> +
> +static const struct iio_chan_spec rm3100_channels[] = {
> +	RM3100_CHANNEL(X, 0),
> +	RM3100_CHANNEL(Y, 1),
> +	RM3100_CHANNEL(Z, 2),
> +	IIO_CHAN_SOFT_TIMESTAMP(3),
> +};
> +
> +static const unsigned long rm3100_scan_masks[] = {GENMASK(2, 0), 0};
> +
> +static IIO_CONST_ATTR_SAMP_FREQ_AVAIL(
> +	"600 300 150 75 37 18 9 4.5 2.3 1.2 0.6 0.3 0.015 0.075"
> +);
> +
> +static struct attribute *rm3100_attributes[] = {
> +	&iio_const_attr_sampling_frequency_available.dev_attr.attr,
> +	NULL,
> +};
> +
> +static const struct attribute_group rm3100_attribute_group = {
> +	.attrs = rm3100_attributes,
> +};
> +
> +#define RM3100_SAMP_NUM			14

Move this to top or .h header file.

> +/*
> + * Frequency : rm3100_samp_rates[][0].rm3100_samp_rates[][1]Hz.
> + * Time between reading: rm3100_sam_rates[][2]ms.
> + * The first one is actually 1.7ms.
> + */
> +static const int rm3100_samp_rates[RM3100_SAMP_NUM][3] = {
> +	{600, 0, 2}, {300, 0, 3}, {150, 0, 7}, {75, 0, 13}, {37, 0, 27},
> +	{18, 0, 55}, {9, 0, 110}, {4, 500000, 220}, {2, 300000, 440},
> +	{1, 200000, 800}, {0, 600000, 1600}, {0, 300000, 3300},
> +	{0, 15000, 6700},  {0, 75000, 13000}
> +};
> +
> +static int rm3100_get_samp_freq(struct rm3100_data *data, int *val, int *val2)
> +{
> +	int ret;
> +	int tmp;
> +
> +	mutex_lock(&data->lock);
> +	ret = regmap_read(data->regmap, RM3100_REG_TMRC, &tmp);
	
	use (unsigned int *) throughly as 3rd argument of
	regmap_read() everywhere.

> +	mutex_unlock(&data->lock);
> +	if (ret < 0)
> +		return ret;
> +	*val = rm3100_samp_rates[tmp - RM3100_TMRC_OFFSET][0];
> +	*val2 = rm3100_samp_rates[tmp - RM3100_TMRC_OFFSET][1];
> +
> +	return IIO_VAL_INT_PLUS_MICRO;
> +}
> +
> +static int rm3100_set_cycle_count(struct rm3100_data *data, int val)
> +{
> +	int ret;
> +	u8 i;
> +
> +	for (i = 0; i < 3; i++) {
> +		ret = regmap_write(data->regmap, RM3100_REG_CC_X + 2 * i, 100);
	
	Would be better to use a descriptive macro for 100 instead ?

> +		if (ret < 0)
> +			return ret;
> +	}
> +	if (val == 50)
> +		data->cycle_count_index = 0;
> +	else if (val == 100)
> +		data->cycle_count_index = 1;
> +	else
> +		data->cycle_count_index = 2;
> +
> +	return 0;
> +}
> +
> +static int rm3100_set_samp_freq(struct rm3100_data *data, int val, int val2)
> +{
> +	struct regmap *regmap = data->regmap;
> +	int cycle_count;
> +	int ret;
> +	int i;
> +
> +	mutex_lock(&data->lock);
> +	/* All cycle count registers use the same value. */
> +	ret = regmap_read(regmap, RM3100_REG_CC_X, &cycle_count);
> +	if (ret < 0)
> +		goto unlock_return;
> +
> +	for (i = 0; i < RM3100_SAMP_NUM; i++) {
> +		if (val == rm3100_samp_rates[i][0] &&
> +		    val2 == rm3100_samp_rates[i][1])
> +			break;
> +	}
> +	if (i == RM3100_SAMP_NUM) {
> +		ret = -EINVAL;
> +		goto unlock_return;
> +	}
> +
> +	ret = regmap_write(regmap, RM3100_REG_TMRC, i + RM3100_TMRC_OFFSET);
> +	if (ret < 0)
> +		goto unlock_return;
> +
> +	/* Checking if cycle count registers need changing. */
> +	if (val == 600 && cycle_count == 200) {
> +		ret = rm3100_set_cycle_count(data, 100);
> +		if (ret < 0)
> +			goto unlock_return;
> +	} else if (val != 600 && cycle_count == 100) {
> +		ret = rm3100_set_cycle_count(data, 200);
> +		if (ret < 0)
> +			goto unlock_return;
> +	}
> +
> +	/* Writing TMRC registers requires CMM reset. */
> +	ret = regmap_write(regmap, RM3100_REG_CMM, 0);
> +	if (ret < 0)
> +		goto unlock_return;
> +	ret = regmap_write(regmap, RM3100_REG_CMM,
> +		RM3100_CMM_X | RM3100_CMM_Y | RM3100_CMM_Z | RM3100_CMM_START);
> +	mutex_unlock(&data->lock);
> +	if (ret < 0)
> +		return ret;
> +
> +	data->conversion_time = rm3100_samp_rates[i][2] + 3000;
> +	return 0;
> +
> +unlock_return:
> +	mutex_unlock(&data->lock);
> +	return ret;
> +}
> +
> +/*
> + * Scale of this sensor depends on cycle count value, these three values
> + * are corresponding to cycle count value 50, 100, 200.
> + * scale = output / gain * 10e4.
			      10^4 ?

> +const static int rm3100_scale[] = {500, 263, 133};
> +
> +static int rm3100_read_raw(struct iio_dev *indio_dev,
> +			   const struct iio_chan_spec *chan,
> +			   int *val, int *val2, long mask)
> +{
> +	struct rm3100_data *data = iio_priv(indio_dev);
> +	int ret;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		ret = iio_device_claim_direct_mode(indio_dev);
> +		if (ret < 0) {
> +			iio_device_release_direct_mode(indio_dev);
> +			return ret;
> +		}
> +		ret = rm3100_read_mag(data, chan->scan_index, val);
> +		iio_device_release_direct_mode(indio_dev);
> +
> +		return ret;
> +	case IIO_CHAN_INFO_SCALE:
> +		*val = 0;
> +		*val2 = rm3100_scale[data->cycle_count_index];
> +
> +		return IIO_VAL_INT_PLUS_MICRO;
> +	case IIO_CHAN_INFO_SAMP_FREQ:
> +		return rm3100_get_samp_freq(data, val, val2);
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int rm3100_write_raw(struct iio_dev *indio_dev,
> +			    struct iio_chan_spec const *chan,
> +			    int val, int val2, long mask)
> +{
> +	struct rm3100_data *data = iio_priv(indio_dev);
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_SAMP_FREQ:
> +		return rm3100_set_samp_freq(data, val, val2);
> +	default:
> +		return -EINVAL;
> +	}
> +
> +}
> +
> +static const struct iio_info rm3100_info = {
> +	.attrs = &rm3100_attribute_group,
> +	.read_raw = rm3100_read_raw,
> +	.write_raw = rm3100_write_raw,
> +};
> +
> +static irqreturn_t rm3100_trigger_handler(int irq, void *p)
> +{
> +	struct iio_poll_func *pf = p;
> +	struct iio_dev *indio_dev = pf->indio_dev;
> +	struct rm3100_data *data = iio_priv(indio_dev);
> +	struct regmap *regmap = data->regmap;
> +	u8 buffer[9];
> +	int ret;
> +	int i;
> +
> +	mutex_lock(&data->lock);
> +	ret = rm3100_wait_measurement(data);
> +	if (ret < 0) {
> +		mutex_unlock(&data->lock);
> +		goto done;
> +	}
> +
> +	ret = regmap_bulk_read(regmap, RM3100_REG_MX2, buffer, sizeof(buffer));
> +	mutex_unlock(&data->lock);
> +	if (ret < 0)
> +		goto done;
> +
> +	/* Convert XXXYYYZZZxxx to XXXxYYYxZZZx. x for padding. */
> +	for (i = 0; i < 3; i++)
> +		memcpy(data->buffer + i * 4, buffer + i * 3, 3);
> +
> +	iio_push_to_buffers_with_timestamp(indio_dev, data->buffer,
> +			iio_get_time_ns(indio_dev));
> +
> +done:
> +	iio_trigger_notify_done(indio_dev->trig);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static void rm3100_remove(void *dh)
> +{
> +	struct rm3100_data *data = (struct rm3100_data *)dh;

No need for an explicit cast to dh.
Void pointer conversions are implicit.

> +	int ret;
> +
> +	ret = regmap_write(data->regmap, RM3100_REG_CMM, 0x00);
> +	if (ret < 0)
> +		dev_err(data->dev, "failed to stop device.\n");
> +}
> +
> +int rm3100_common_probe(struct device *dev, struct regmap *regmap, int irq)
> +{
> +	struct iio_dev *indio_dev;
> +	struct rm3100_data *data;
> +	int tmp;
> +	int ret;
> +
> +	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	data = iio_priv(indio_dev);
> +	data->dev = dev;

Check this if it's really required and possible remove
the `struct device *dev` from the private chip data struct.

Use can use `regmap_get_device()` for `rm3100_remove()`

> +	data->regmap = regmap;
> +	data->buffer = devm_kzalloc(dev, RM3100_SCAN_BYTES, GFP_KERNEL);
> +	if (!data->buffer)
> +		return -ENOMEM;
> +
> +	mutex_init(&data->lock);
> +
> +	indio_dev->dev.parent = dev;
> +	indio_dev->name = "rm3100";
> +	indio_dev->info = &rm3100_info;
> +	indio_dev->channels = rm3100_channels;
> +	indio_dev->num_channels = ARRAY_SIZE(rm3100_channels);
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +	indio_dev->available_scan_masks = rm3100_scan_masks;
> +
> +	if (!irq)
> +		data->use_interrupt = false;
> +	else {
> +		data->use_interrupt = true;
> +		ret = devm_request_irq(dev,
> +				       irq,
> +				       rm3100_irq_handler,
> +				       IRQF_TRIGGER_RISING,
> +				       indio_dev->name,
> +				       data);
> +		if (ret < 0) {
> +			dev_err(dev, "request irq line failed.\n");
> +			return ret;
> +		}
> +		init_completion(&data->measuring_done);
> +	}
> +
> +	ret = devm_iio_triggered_buffer_setup(dev, indio_dev, NULL,
> +					      rm3100_trigger_handler, NULL);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* 3sec more wait time. */
> +	ret = regmap_read(regmap, RM3100_REG_TMRC, &tmp);
> +	if (ret < 0)
> +		return ret;
> +	data->conversion_time =
> +		rm3100_samp_rates[tmp-RM3100_TMRC_OFFSET][2] + 3000;

This will fit in 80 char limit.

> +	/* Cycle count values may not be what we want. */
> +	ret = regmap_read(data->regmap, RM3100_REG_TMRC, &tmp);
> +	if (ret < 0)
> +		return ret;
> +	if ((tmp - RM3100_TMRC_OFFSET) == 0)
> +		rm3100_set_cycle_count(data, 100);
> +	else
> +		rm3100_set_cycle_count(data, 200);
> +
> +	/* Starting all channels' conversion. */
> +	ret = regmap_write(regmap, RM3100_REG_CMM,
> +		RM3100_CMM_X | RM3100_CMM_Y | RM3100_CMM_Z | RM3100_CMM_START);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = devm_iio_device_register(dev, indio_dev);
> +	if (ret < 0)
> +		return ret;
> +
> +	return devm_add_action(dev, rm3100_remove, data);
> +}
> +EXPORT_SYMBOL_GPL(rm3100_common_probe);
> +
> +MODULE_AUTHOR("Song Qiang <songqiang1304521@gmail.com>");
> +MODULE_DESCRIPTION("PNI RM3100 3-axis magnetometer i2c driver");
> +MODULE_LICENSE("GPL v2");
> diff --git a/drivers/iio/magnetometer/rm3100-i2c.c b/drivers/iio/magnetometer/rm3100-i2c.c
> new file mode 100644
> index 000000000000..e8b84fac771b
> --- /dev/null
> +++ b/drivers/iio/magnetometer/rm3100-i2c.c
> @@ -0,0 +1,58 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Support for PNI RM3100 3-axis geomagnetic sensor a i2c bus.
> + *
> + * Copyright (C) 2018 Song Qiang <songqiang1304521@gmail.com>
> + *
> + * i2c slave address 0x20 + SA1 << 1 + SA0.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/i2c.h>
> +
> +#include "rm3100.h"
> +
> +static const struct regmap_config rm3100_regmap_config = {
> +	.reg_bits = 8,
> +	.val_bits = 8,
> +
> +	.rd_table = &rm3100_readable_table,
> +	.wr_table = &rm3100_writable_table,
> +	.volatile_table = &rm3100_volatile_table,
> +
> +	.cache_type = REGCACHE_RBTREE,

I wonder when do we use other types of `.cache_type` ?

> +static int rm3100_probe(struct i2c_client *client)
> +{
> +	struct regmap *regmap;
> +
> +	if (!i2c_check_functionality(client->adapter,
> +		I2C_FUNC_SMBUS_READ_I2C_BLOCK | I2C_FUNC_SMBUS_BYTE_DATA))
> +		return -EOPNOTSUPP;
> +
> +	regmap =  devm_regmap_init_i2c(client, &rm3100_regmap_config);
> +	if (IS_ERR(regmap))
> +		return PTR_ERR(regmap);
> +
> +	return rm3100_common_probe(&client->dev, regmap, client->irq);
> +}
> +
> +static const struct of_device_id rm3100_dt_match[] = {
> +	{ .compatible = "pni,rm3100", },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(of, rm3100_dt_match);
> +
> +static struct i2c_driver rm3100_driver = {
> +	.driver = {
> +		.name = "rm3100-i2c",
> +		.of_match_table = rm3100_dt_match,
> +	},
> +	.probe_new = rm3100_probe,
> +};
> +module_i2c_driver(rm3100_driver);
> +
> +MODULE_AUTHOR("Song Qiang <songqiang1304521@gmail.com>");
> +MODULE_DESCRIPTION("PNI RM3100 3-axis magnetometer i2c driver");
> +MODULE_LICENSE("GPL v2");
> diff --git a/drivers/iio/magnetometer/rm3100-spi.c b/drivers/iio/magnetometer/rm3100-spi.c
> new file mode 100644
> index 000000000000..1a7a69fb9872
> --- /dev/null
> +++ b/drivers/iio/magnetometer/rm3100-spi.c
> @@ -0,0 +1,64 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Support for PNI RM3100 3-axis geomagnetic sensor a spi bus.
> + *
> + * Copyright (C) 2018 Song Qiang <songqiang1304521@gmail.com>
> + */
> +
> +#include <linux/module.h>
> +#include <linux/spi/spi.h>
> +
> +#include "rm3100.h"
> +
> +static const struct regmap_config rm3100_regmap_config = {
> +	.reg_bits = 8,
> +	.val_bits = 8,
> +
> +	.rd_table = &rm3100_readable_table,
> +	.wr_table = &rm3100_writable_table,
> +	.volatile_table = &rm3100_volatile_table,
> +
> +	.read_flag_mask = 0x80,
> +
> +	.cache_type = REGCACHE_RBTREE,
> +};
> +
> +static int rm3100_probe(struct spi_device *spi)
> +{
> +	struct regmap *regmap;
> +	int ret;
> +
> +	/* Actually this device supports both mode 0 and mode 3. */
> +	spi->mode = SPI_MODE_0;
> +	/* Data rates cannot exceed 1Mbits. */
> +	spi->max_speed_hz = 1000000;
> +	spi->bits_per_word = 8;
> +	ret = spi_setup(spi);
> +	if (ret)
> +		return ret;
> +
> +	regmap =  devm_regmap_init_spi(spi, &rm3100_regmap_config);
> +	if (IS_ERR(regmap))
> +		return PTR_ERR(regmap);
> +
> +	return rm3100_common_probe(&spi->dev, regmap, spi->irq);
> +}
> +
> +static const struct of_device_id rm3100_dt_match[] = {
> +	{ .compatible = "pni,rm3100", },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(of, rm3100_dt_match);
> +
> +static struct spi_driver rm3100_driver = {
> +	.driver = {
> +		.name = "rm3100-spi",
> +		.of_match_table = rm3100_dt_match,
> +	},
> +	.probe = rm3100_probe,
> +};
> +module_spi_driver(rm3100_driver);
> +
> +MODULE_AUTHOR("Song Qiang <songqiang1304521@gmail.com>");
> +MODULE_DESCRIPTION("PNI RM3100 3-axis magnetometer spi driver");
> +MODULE_LICENSE("GPL v2");
> diff --git a/drivers/iio/magnetometer/rm3100.h b/drivers/iio/magnetometer/rm3100.h
> new file mode 100644
> index 000000000000..673647574add
> --- /dev/null
> +++ b/drivers/iio/magnetometer/rm3100.h
> @@ -0,0 +1,73 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Header file for PNI RM3100 driver

Remove this bogus line.

> + * Copyright (C) 2018 Song Qiang <songqiang1304521@gmail.com>
> + */
> +
> +#ifndef RM3100_CORE_H
> +#define RM3100_CORE_H
> +
> +#include <linux/regmap.h>
> +
> +#define RM3100_REG_REV_ID		0x36

Does this ID needs to be checked and validated during 
intialisation with default state ID val ?

> +
> +/* Cycle Count Registers. */
> +#define RM3100_REG_CC_X			0x05
> +#define RM3100_REG_CC_Y			0x07
> +#define RM3100_REG_CC_Z			0x09
> +
> +/* Continues Measurement Mode register. */

Is it continuous ?

> +#define RM3100_REG_CMM			0x01
> +#define RM3100_CMM_START		BIT(0)
> +#define RM3100_CMM_X			BIT(4)
> +#define RM3100_CMM_Y			BIT(5)
> +#define RM3100_CMM_Z			BIT(6)
> +
> +/* TiMe Rate Configuration register. */

Time!

> +#define RM3100_REG_TMRC			0x0B
> +#define RM3100_TMRC_OFFSET		0x92
> +
> +/* Result Status register. */
> +#define RM3100_REG_STATUS		0x34
> +#define RM3100_STATUS_DRDY		BIT(7)

If this status bit is a field of status register then
align this as:

#define RM3100_REG_STATUS		0x34
#define	 RM3100_STATUS_DRDY		BIT(7)



> +/* Measurement result registers. */
> +#define RM3100_REG_MX2			0x24
> +#define RM3100_REG_MY2			0x27
> +#define RM3100_REG_MZ2			0x2a
> +
> +#define RM3100_W_REG_START		RM3100_REG_CMM
> +#define RM3100_W_REG_END		RM3100_REG_REV_ID
> +#define RM3100_R_REG_START		RM3100_REG_CMM
> +#define RM3100_R_REG_END		RM3100_REG_STATUS
> +#define RM3100_V_REG_START		RM3100_REG_MX2
> +#define RM3100_V_REG_END		RM3100_REG_STATUS
> +
> +#define RM3100_SCAN_BYTES		24
> +
> +struct rm3100_data {
> +	struct device *dev;

Better remove this ?

On Tue, Sep 25, 2018 at 02:30:54PM +0100, Jonathan Cameron wrote:
> On Tue, 25 Sep 2018 11:17:24 +0800
> Song Qiang <songqiang1304521@gmail.com> wrote:
> 
> > PNI RM3100 is a high resolution, large signal immunity magnetometer,
> > composed of 3 single sensors and a processing chip with MagI2C Interface.
> > 
> > Following functions are available:
> > - Single-shot measurement from
> >   /sys/bus/iio/devices/iio:deviceX/in_magn_{axis}_raw
> > - Triggerd buffer measurement.
> > - Both i2c and spi interface are supported.
> > - Both interrupt and polling measurement is supported, depands on if
> >   the 'interrupts' in DT is declared.
> > 
> > Signed-off-by: Song Qiang <songqiang1304521@gmail.com>
> Various minor comments inline.  Definitely heading in the right direction.
> 
> Good work.
> 
> Thanks,
> 
> Jonathan
> 

...

> > +static int rm3100_get_samp_freq(struct rm3100_data *data, int *val, int *val2)
> > +{
> > +	int ret;
> > +	int tmp;
> > +
> > +	mutex_lock(&data->lock);
> > +	ret = regmap_read(data->regmap, RM3100_REG_TMRC, &tmp);
> > +	mutex_unlock(&data->lock);
> > +	if (ret < 0)
> > +		return ret;
> > +	*val = rm3100_samp_rates[tmp - RM3100_TMRC_OFFSET][0];
> > +	*val2 = rm3100_samp_rates[tmp - RM3100_TMRC_OFFSET][1];
> > +
> > +	return IIO_VAL_INT_PLUS_MICRO;
> > +}
> > +
> > +static int rm3100_set_cycle_count(struct rm3100_data *data, int val)
> > +{
> > +	int ret;
> > +	u8 i;
> > +
> > +	for (i = 0; i < 3; i++) {
> > +		ret = regmap_write(data->regmap, RM3100_REG_CC_X + 2 * i, 100);
> 
> Does this write it to the same value irrespective of the value of val?
> Seems odd.
> 
Hi Jonathan,

Sometimes I see these mistakes I couldn't stop laughing at my stupiness.
Should be val, my mistake submitting without a throughout functional
check, I think I'll write a script to prevent this from happening again.

> > +		if (ret < 0)
> > +			return ret;
> > +	}
> > +	if (val == 50)
> 
> Switch would be nicer.  Also why have all other values call back to
> 2 rather than generating an error?
> 
I could have given it an error path, but I checked the code, 'val' in
this function is always given by my code. I think this leads no
possibility for val to go wrong. Do I still need an error path in this
circumstance?

> > +		data->cycle_count_index = 0;
> > +	else if (val == 100)
> > +		data->cycle_count_index = 1;
> > +	else
> > +		data->cycle_count_index = 2;
> > +
> > +	return 0;
> > +}
> > +
> > +static int rm3100_set_samp_freq(struct rm3100_data *data, int val, int val2)
> > +{
> > +	struct regmap *regmap = data->regmap;
> > +	int cycle_count;
> > +	int ret;
> > +	int i;
> > +
> > +	mutex_lock(&data->lock);
> 
> Why are you taking this lock? It's not well documented what it protects
> so it's not clear in this path why it is taken.
> (hint add a comment to the definition of the lock to make it clear!)
> - note I'm not saying it shouldn't be taken here, just that there is no
> comment to justify it..
> 
When I was considering the lock, I read Robert Love's 'Linux Kernel
Development', whose chapter 9 talks about how to understand the lock.
It was talking about protecting data, but in here, my purpose is to
protect the i2c execution consistency. I think it may be possible that
one person is extracting the data while another person is planning set
the frequency. Setting the frequency within queuing data will causing
CMM(Continuous Measurement Mode) register reset, breaking the measurement
process. That's why I added lock to callbacks where a i2c sequence can
happen. I referred code from hmc5843, which did the similar lock stuff,
am I understanding about lock right?

> > +	/* All cycle count registers use the same value. */
> > +	ret = regmap_read(regmap, RM3100_REG_CC_X, &cycle_count);
> > +	if (ret < 0)
> > +		goto unlock_return;
> > +
> > +	for (i = 0; i < RM3100_SAMP_NUM; i++) {
> > +		if (val == rm3100_samp_rates[i][0] &&
> > +		    val2 == rm3100_samp_rates[i][1])
> > +			break;
> > +	}
> > +	if (i == RM3100_SAMP_NUM) {
> > +		ret = -EINVAL;
> > +		goto unlock_return;
> > +	}
> > +
> > +	ret = regmap_write(regmap, RM3100_REG_TMRC, i + RM3100_TMRC_OFFSET);
> > +	if (ret < 0)
> > +		goto unlock_return;

...

> > +	if (ret < 0)
> > +		goto done;
> > +
> > +	/* Convert XXXYYYZZZxxx to XXXxYYYxZZZx. x for padding. */
> > +	for (i = 0; i < 3; i++)
> > +		memcpy(data->buffer + i * 4, buffer + i * 3, 3);
> 
> Firstly X doesn't need copying.
> Secondly the copy of Y actually overwrites the value of Z
> XXXYYYZZZxxx
> XXXxYYYZZxxx
> XXXxYYYxYZZx
> 
> I think...
> 
They are in different memories, buffer is a temporary memory for data
reading out, data->buffer is for pushing to the userspace.

> > +
> > +	iio_push_to_buffers_with_timestamp(indio_dev, data->buffer,
> > +			iio_get_time_ns(indio_dev));
> 
> Align with opening bracket. 
> 
> > +
> > +done:
> > +	iio_trigger_notify_done(indio_dev->trig);
> > +
> > +	return IRQ_HANDLED;
> > +}
> > +
> > +static void rm3100_remove(void *dh)
> > +{
> > +	struct rm3100_data *data = (struct rm3100_data *)dh;
> > +	int ret;
> > +
> > +	ret = regmap_write(data->regmap, RM3100_REG_CMM, 0x00);
> > +	if (ret < 0)
> > +		dev_err(data->dev, "failed to stop device.\n");
> > +}
> > +
> > +int rm3100_common_probe(struct device *dev, struct regmap *regmap, int irq)
> > +{
> > +	struct iio_dev *indio_dev;
> > +	struct rm3100_data *data;
> > +	int tmp;
> > +	int ret;
> > +
> > +	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
> > +	if (!indio_dev)
> > +		return -ENOMEM;
> > +
> > +	data = iio_priv(indio_dev);
> > +	data->dev = dev;
> > +	data->regmap = regmap;
> > +	data->buffer = devm_kzalloc(dev, RM3100_SCAN_BYTES, GFP_KERNEL);
> > +	if (!data->buffer)
> > +		return -ENOMEM;
> > +
> > +	mutex_init(&data->lock);
> > +
> > +	indio_dev->dev.parent = dev;
> > +	indio_dev->name = "rm3100";
> > +	indio_dev->info = &rm3100_info;
> > +	indio_dev->channels = rm3100_channels;
> > +	indio_dev->num_channels = ARRAY_SIZE(rm3100_channels);
> > +	indio_dev->modes = INDIO_DIRECT_MODE;
> > +	indio_dev->available_scan_masks = rm3100_scan_masks;
> > +
> > +	if (!irq)
> > +		data->use_interrupt = false;
> > +	else {
> > +		data->use_interrupt = true;
> > +		ret = devm_request_irq(dev,
> > +				       irq,
> > +				       rm3100_irq_handler,
> > +				       IRQF_TRIGGER_RISING,
> > +				       indio_dev->name,
> > +				       data);
> > +		if (ret < 0) {
> > +			dev_err(dev, "request irq line failed.\n");
> > +			return ret;
> > +		}
> > +		init_completion(&data->measuring_done);
> > +	}
> > +
> > +	ret = devm_iio_triggered_buffer_setup(dev, indio_dev, NULL,
> > +					      rm3100_trigger_handler, NULL);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	/* 3sec more wait time. */
> 
> I have no idea what this comment is referring to..
> Not seeing any waiting here...
> 
The thing is, measurement time of this sensor span from ~1.7ms to ~13
seconds. I'll need a wait time for *_wait_measurement(), and I use
measurement time + 3 seconds for waiting time. This is an initialization.
Usage of this is in *_wait_measurement.

yours,
Song Qiang

> > +	ret = regmap_read(regmap, RM3100_REG_TMRC, &tmp);
> > +	if (ret < 0)
> > +		return ret;
> > +	data->conversion_time =
> > +		rm3100_samp_rates[tmp-RM3100_TMRC_OFFSET][2] + 3000;
> 
> spacing around -  
> Please check this throughout.

...

On Tue, Sep 25, 2018 at 10:36:54PM +0800, Phil Reid wrote:
> On 25/09/2018 9:30 PM, Jonathan Cameron wrote:
> > > +static irqreturn_t rm3100_trigger_handler(int irq, void *p)
> > > +{
> > > +	struct iio_poll_func *pf = p;
> > > +	struct iio_dev *indio_dev = pf->indio_dev;
> > > +	struct rm3100_data *data = iio_priv(indio_dev);
> > > +	struct regmap *regmap = data->regmap;
> > > +	u8 buffer[9];
> > > +	int ret;
> > > +	int i;
> > > +
> > > +	mutex_lock(&data->lock);
> > > +	ret = rm3100_wait_measurement(data);
> > > +	if (ret < 0) {
> > > +		mutex_unlock(&data->lock);
> > > +		goto done;
> > > +	}
> > > +
> > > +	ret = regmap_bulk_read(regmap, RM3100_REG_MX2, buffer, sizeof(buffer));
> > > +	mutex_unlock(&data->lock);
> > > +	if (ret < 0)
> > > +		goto done;
> > > +
> > > +	/* Convert XXXYYYZZZxxx to XXXxYYYxZZZx. x for padding. */
> > > +	for (i = 0; i < 3; i++)
> > > +		memcpy(data->buffer + i * 4, buffer + i * 3, 3);
> > Firstly X doesn't need copying.
> > Secondly the copy of Y actually overwrites the value of Z
> > XXXYYYZZZxxx
> > XXXxYYYZZxxx
> > XXXxYYYxYZZx
> > 
> > I think...
> > 
> > > +
> > > +	iio_push_to_buffers_with_timestamp(indio_dev, data->buffer,
> > > +			iio_get_time_ns(indio_dev));
> 
> memcpy target is a different buffer so should be ok.
> 
> But that raises the question of does it need to be?
> 'buffer' could be 12 bytes long and just shuffle Z then Y.
> Do the unused bytes need to be zeroed? or does libiio mask them anyway?
> 
> 
> 
> -- 
> Regards
> Phil Reid

Hi Phil,

This is interesting, last patch I submitted uses three transactions and
shuffles X, Y and Z respectively. You said it should be better to use one
transactions, I thought it makes point, and one transaction may reduce
IO pressure of the i2c bus. :)
And that's not necessary for unused bytes to be zero. I'm not familiar
with libiio, actually just been studying it, can't say anything about
it.

yours,
Song Qiang

On Tue, Sep 25, 2018 at 11:20:18PM +0530, Himanshu Jha wrote:
> On Tue, Sep 25, 2018 at 11:17:24AM +0800, Song Qiang wrote:
> > PNI RM3100 is a high resolution, large signal immunity magnetometer,
> > composed of 3 single sensors and a processing chip with MagI2C Interface.
> > 
> > Following functions are available:
> > - Single-shot measurement from
> >   /sys/bus/iio/devices/iio:deviceX/in_magn_{axis}_raw
> > - Triggerd buffer measurement.
> > - Both i2c and spi interface are supported.
> > - Both interrupt and polling measurement is supported, depands on if
> 							 depends
> 

...

> +
> > +static int rm3100_wait_measurement(struct rm3100_data *data)
> > +{
> > +	struct regmap *regmap = data->regmap;
> > +	unsigned int val;
> > +	int tries = 20;
> > +	int ret;
> > +
> > +	/*
> > +	 * A read cycle of 400kbits i2c; bus is about 20us, plus the time
> 				      ; was mistakenly added ?
> 

Hi Himanshu,

Oops, it shouldn't be there.

> > +	 * used for scheduling, a read cycle of fast mode of this device
> > +	 * can reach 1.7ms, it may be possible for data to arrive just
> > +	 * after we check the RM3100_REG_STATUS. In this case, irq_handler is
> > +	 * called before measuring_done is reinitialized, it will wait
> > +	 * forever for data that has already been ready.
> > +	 * Reinitialize measuring_done before looking up makes sure we
> > +	 * will always capture interrupt no matter when it happened.
> > +	 */
> > +	if (data->use_interrupt)
> > +		reinit_completion(&data->measuring_done);
> > +

...

> > +static const struct attribute_group rm3100_attribute_group = {
> > +	.attrs = rm3100_attributes,
> > +};
> > +
> > +#define RM3100_SAMP_NUM			14
> 
> Move this to top or .h header file.
> 

I could have move it to the top, but the only related section is
here. It only changes if a new frequency is supported, which seems
not possible from now. Just here to tell the readers how many
frequencies are in the array. So if one day a new frequency is
supported, we can change it easily.

> > +/*
> > + * Frequency : rm3100_samp_rates[][0].rm3100_samp_rates[][1]Hz.
> > + * Time between reading: rm3100_sam_rates[][2]ms.
> > + * The first one is actually 1.7ms.
> > + */
> > +static const int rm3100_samp_rates[RM3100_SAMP_NUM][3] = {
> > +	{600, 0, 2}, {300, 0, 3}, {150, 0, 7}, {75, 0, 13}, {37, 0, 27},
> > +	{18, 0, 55}, {9, 0, 110}, {4, 500000, 220}, {2, 300000, 440},
> > +	{1, 200000, 800}, {0, 600000, 1600}, {0, 300000, 3300},
> > +	{0, 15000, 6700},  {0, 75000, 13000}
> > +};
> > +
> > +static int rm3100_get_samp_freq(struct rm3100_data *data, int *val, int *val2)
> > +{
> > +	int ret;
> > +	int tmp;
> > +
> > +	mutex_lock(&data->lock);
> > +	ret = regmap_read(data->regmap, RM3100_REG_TMRC, &tmp);
> 	
> 	use (unsigned int *) throughly as 3rd argument of
> 	regmap_read() everywhere.
> 
> > +	mutex_unlock(&data->lock);
> > +	if (ret < 0)
> > +		return ret;
> > +	*val = rm3100_samp_rates[tmp - RM3100_TMRC_OFFSET][0];
> > +	*val2 = rm3100_samp_rates[tmp - RM3100_TMRC_OFFSET][1];
> > +
> > +	return IIO_VAL_INT_PLUS_MICRO;
> > +}
> > +
> > +static int rm3100_set_cycle_count(struct rm3100_data *data, int val)
> > +{
> > +	int ret;
> > +	u8 i;
> > +
> > +	for (i = 0; i < 3; i++) {
> > +		ret = regmap_write(data->regmap, RM3100_REG_CC_X + 2 * i, 100);
> 	
> 	Would be better to use a descriptive macro for 100 instead ?
> 

This was a mistake, my fault.

> > +		if (ret < 0)
> > +			return ret;
> > +	}
> > +	if (val == 50)
> > +		data->cycle_count_index = 0;
> > +	else if (val == 100)
> > +		data->cycle_count_index = 1;
> > +	else
> > +		data->cycle_count_index = 2;

...

> > +static const struct regmap_config rm3100_regmap_config = {
> > +	.reg_bits = 8,
> > +	.val_bits = 8,
> > +
> > +	.rd_table = &rm3100_readable_table,
> > +	.wr_table = &rm3100_writable_table,
> > +	.volatile_table = &rm3100_volatile_table,
> > +
> > +	.cache_type = REGCACHE_RBTREE,
> 
> I wonder when do we use other types of `.cache_type` ?
> 

Interesting question...

> > +static int rm3100_probe(struct i2c_client *client)
> > +{
> > +	struct regmap *regmap;
> > +

...

> > +
> > +#ifndef RM3100_CORE_H
> > +#define RM3100_CORE_H
> > +
> > +#include <linux/regmap.h>
> > +
> > +#define RM3100_REG_REV_ID		0x36
> 
> Does this ID needs to be checked and validated during 
> intialisation with default state ID val ?
> 

No, should remove it.

> > +
> > +/* Cycle Count Registers. */
> > +#define RM3100_REG_CC_X			0x05
> > +#define RM3100_REG_CC_Y			0x07
> > +#define RM3100_REG_CC_Z			0x09
> > +
> > +/* Continues Measurement Mode register. */
> 
> Is it continuous ?
> 
> > +#define RM3100_REG_CMM			0x01
> > +#define RM3100_CMM_START		BIT(0)
> > +#define RM3100_CMM_X			BIT(4)
> > +#define RM3100_CMM_Y			BIT(5)
> > +#define RM3100_CMM_Z			BIT(6)
> > +
> > +/* TiMe Rate Configuration register. */
> 
> Time!
> 
These uppercase letters are explaining why the register is called TMRC,
T(i)M(e) R(ate) C(onfiguration). :)
Though my bad english do carry a lot spell mistakes here...

> > +#define RM3100_REG_TMRC			0x0B
> > +#define RM3100_TMRC_OFFSET		0x92
> > +
> > +/* Result Status register. */
> > +#define RM3100_REG_STATUS		0x34
> > +#define RM3100_STATUS_DRDY		BIT(7)
> 
> If this status bit is a field of status register then
> align this as:
> 
> #define RM3100_REG_STATUS		0x34
> #define	 RM3100_STATUS_DRDY		BIT(7)
> 
> 
> 
> > +/* Measurement result registers. */
> > +#define RM3100_REG_MX2			0x24
> > +#define RM3100_REG_MY2			0x27
> > +#define RM3100_REG_MZ2			0x2a
> > +
> > +#define RM3100_W_REG_START		RM3100_REG_CMM
> > +#define RM3100_W_REG_END		RM3100_REG_REV_ID
> > +#define RM3100_R_REG_START		RM3100_REG_CMM
> > +#define RM3100_R_REG_END		RM3100_REG_STATUS
> > +#define RM3100_V_REG_START		RM3100_REG_MX2
> > +#define RM3100_V_REG_END		RM3100_REG_STATUS
> > +
> > +#define RM3100_SCAN_BYTES		24
> > +
> > +struct rm3100_data {
> > +	struct device *dev;
> 
> Better remove this ?
> 
All applied in the next patch. :)
> 
> -- 
> Himanshu Jha
> Undergraduate Student
> Department of Electronics & Communication
> Guru Tegh Bahadur Institute of Technology

yours,
Song Qiang

On 26/09/2018 9:49 AM, Song Qiang wrote:
> On Tue, Sep 25, 2018 at 10:36:54PM +0800, Phil Reid wrote:
>> On 25/09/2018 9:30 PM, Jonathan Cameron wrote:
>>>> +static irqreturn_t rm3100_trigger_handler(int irq, void *p)
>>>> +{
>>>> +	struct iio_poll_func *pf = p;
>>>> +	struct iio_dev *indio_dev = pf->indio_dev;
>>>> +	struct rm3100_data *data = iio_priv(indio_dev);
>>>> +	struct regmap *regmap = data->regmap;
>>>> +	u8 buffer[9];
>>>> +	int ret;
>>>> +	int i;
>>>> +
>>>> +	mutex_lock(&data->lock);
>>>> +	ret = rm3100_wait_measurement(data);
>>>> +	if (ret < 0) {
>>>> +		mutex_unlock(&data->lock);
>>>> +		goto done;
>>>> +	}
>>>> +
>>>> +	ret = regmap_bulk_read(regmap, RM3100_REG_MX2, buffer, sizeof(buffer));
>>>> +	mutex_unlock(&data->lock);
>>>> +	if (ret < 0)
>>>> +		goto done;
>>>> +
>>>> +	/* Convert XXXYYYZZZxxx to XXXxYYYxZZZx. x for padding. */
>>>> +	for (i = 0; i < 3; i++)
>>>> +		memcpy(data->buffer + i * 4, buffer + i * 3, 3);
>>> Firstly X doesn't need copying.
>>> Secondly the copy of Y actually overwrites the value of Z
>>> XXXYYYZZZxxx
>>> XXXxYYYZZxxx
>>> XXXxYYYxYZZx
>>>
>>> I think...
>>>
>>>> +
>>>> +	iio_push_to_buffers_with_timestamp(indio_dev, data->buffer,
>>>> +			iio_get_time_ns(indio_dev));
>>
>> memcpy target is a different buffer so should be ok.
>>
>> But that raises the question of does it need to be?
>> 'buffer' could be 12 bytes long and just shuffle Z then Y.
>> Do the unused bytes need to be zeroed? or does libiio mask them anyway?
>>
>>
>>
>> -- 
>> Regards
>> Phil Reid
> 
> Hi Phil,
> 
> This is interesting, last patch I submitted uses three transactions and
> shuffles X, Y and Z respectively. You said it should be better to use one
> transactions, I thought it makes point, and one transaction may reduce
> IO pressure of the i2c bus. :)
> And that's not necessary for unused bytes to be zero. I'm not familiar
> with libiio, actually just been studying it, can't say anything about
> it.
> 
> yours,
> Song Qiang
> 
> 
G'day Song,

yes the one transaction suggestion was to reduce pressure on the bus.
I think also with 3 calls you can up up with other devices taking over
the i2c / spi bus in between.

We've got a devkit for this part, but haven't got to wiring it up to our system as yet.
We're looking at using the i2c interface which could push things at max samplerate, so yes I'm
keen to see bus pressure reduced as much as possible.

I was thinking something like the following:

u8 buffer[12];
regmap_bulk_read(regmap, RM3100_REG_MX2, buffer, 9);

buffer[10] = buffer[8]; // or memcpy or some other fancy shuffle code.
buffer[9]  = buffer[7];
buffer[8]  = buffer[6];

buffer[6]  = buffer[5];
buffer[5]  = buffer[4];
buffer[4]  = buffer[3];

iio_push_to_buffers_with_timestamp(indio_dev, buffer, iio_get_time_ns(indio_dev));

but I'm unsure if this would be needed:
buffer[7] = 0
buffer[3] = 0

What you've got does the job I think.

I haven't dug into the datasheet in great detail, and my iio knownledge is limited.
Are you sure the RM3100_CHANNEL scantype endianness is IIO_LE.
rm3100_read_mag looks to be doing big endian conversion and the datasheet agrees with that.

On Wed, Sep 26, 2018 at 10:30:34AM +0800, Phil Reid wrote:
> On 26/09/2018 9:49 AM, Song Qiang wrote:
> > On Tue, Sep 25, 2018 at 10:36:54PM +0800, Phil Reid wrote:
> > > On 25/09/2018 9:30 PM, Jonathan Cameron wrote:
> > > > > +static irqreturn_t rm3100_trigger_handler(int irq, void *p)
> > > > > +{
> > > > > +	struct iio_poll_func *pf = p;
> > > > > +	struct iio_dev *indio_dev = pf->indio_dev;
> > > > > +	struct rm3100_data *data = iio_priv(indio_dev);
> > > > > +	struct regmap *regmap = data->regmap;
> > > > > +	u8 buffer[9];
> > > > > +	int ret;
> > > > > +	int i;
> > > > > +
> > > > > +	mutex_lock(&data->lock);
> > > > > +	ret = rm3100_wait_measurement(data);
> > > > > +	if (ret < 0) {
> > > > > +		mutex_unlock(&data->lock);
> > > > > +		goto done;
> > > > > +	}
> > > > > +
> > > > > +	ret = regmap_bulk_read(regmap, RM3100_REG_MX2, buffer, sizeof(buffer));
> > > > > +	mutex_unlock(&data->lock);
> > > > > +	if (ret < 0)
> > > > > +		goto done;
> > > > > +
> > > > > +	/* Convert XXXYYYZZZxxx to XXXxYYYxZZZx. x for padding. */
> > > > > +	for (i = 0; i < 3; i++)
> > > > > +		memcpy(data->buffer + i * 4, buffer + i * 3, 3);
> > > > Firstly X doesn't need copying.
> > > > Secondly the copy of Y actually overwrites the value of Z
> > > > XXXYYYZZZxxx
> > > > XXXxYYYZZxxx
> > > > XXXxYYYxYZZx
> > > > 
> > > > I think...
> > > > 
> > > > > +
> > > > > +	iio_push_to_buffers_with_timestamp(indio_dev, data->buffer,
> > > > > +			iio_get_time_ns(indio_dev));
> > > 
> > > memcpy target is a different buffer so should be ok.
> > > 
> > > But that raises the question of does it need to be?
> > > 'buffer' could be 12 bytes long and just shuffle Z then Y.
> > > Do the unused bytes need to be zeroed? or does libiio mask them anyway?
> > > 
> > > 
> > > 
> > > -- 
> > > Regards
> > > Phil Reid
> > 
> > Hi Phil,
> > 
> > This is interesting, last patch I submitted uses three transactions and
> > shuffles X, Y and Z respectively. You said it should be better to use one
> > transactions, I thought it makes point, and one transaction may reduce
> > IO pressure of the i2c bus. :)
> > And that's not necessary for unused bytes to be zero. I'm not familiar
> > with libiio, actually just been studying it, can't say anything about
> > it.
> > 
> > yours,
> > Song Qiang
> > 
> > 
> G'day Song,
> 
> yes the one transaction suggestion was to reduce pressure on the bus.
> I think also with 3 calls you can up up with other devices taking over
> the i2c / spi bus in between.
> 
> We've got a devkit for this part, but haven't got to wiring it up to our system as yet.
> We're looking at using the i2c interface which could push things at max samplerate, so yes I'm
> keen to see bus pressure reduced as much as possible.
> 
> I was thinking something like the following:
> 
> u8 buffer[12];
> regmap_bulk_read(regmap, RM3100_REG_MX2, buffer, 9);
> 
> buffer[10] = buffer[8]; // or memcpy or some other fancy shuffle code.
> buffer[9]  = buffer[7];
> buffer[8]  = buffer[6];
> 
> buffer[6]  = buffer[5];
> buffer[5]  = buffer[4];
> buffer[4]  = buffer[3];
> 
> iio_push_to_buffers_with_timestamp(indio_dev, buffer, iio_get_time_ns(indio_dev));
> 
> but I'm unsure if this would be needed:
> buffer[7] = 0
> buffer[3] = 0
> 
> What you've got does the job I think.
> 
> I haven't dug into the datasheet in great detail, and my iio knownledge is limited.
> Are you sure the RM3100_CHANNEL scantype endianness is IIO_LE.
> rm3100_read_mag looks to be doing big endian conversion and the datasheet agrees with that.
> 
> 
> -- 
> Regards
> Phil Reid
> 

Hi Phil,

You're absolutely right!
This should be big endian, I think I probably just want something there
when I was writing this code, planned to change it later, but apparently
I've forgotten it...

AFAIK, filling places we do not need with 0 is not needed, we just
extract valid data from valid bit field(24 here).

Both one transaction and three transactions way have their point, but
this is a OS, probably the spiltted one is better, I need some real
thinking about this...

I could have use the same buffer to read from the sensor and send it to
userspace like this:

int i = 0;
ret = regmap_bulk_read(regmap, RM3100_REG_MX2, 9);
if(ret)
	...
/* Convert XXXYYYZZZxxx to XXXxYYYxZZZx. */
for (i = 0; i < 2; i++)
	memcpy(buffer + (2 - i) * 4, buffer + (2 - i) * 3), 3);

This code snippet will use the same buffer, actually that's what I was
using the first time. Jonathan must thinks so, from what he commented,
he assumed I was using the same buffer, also what you want.
But I changed this due to Peter's comment, maybe not a big deal, he
suggests to use sizeof(buffer), this makes me use an additional size 9
buffer. I thought this doesn't matter too much, just some additional
space from the stack, but now I think maybe less memory using would be
better...
After all, this length 9 seems like never shouldn't be changed...

yours,
Song Qiang

On 26/09/2018 4:09 PM, Song Qiang wrote:
> On Wed, Sep 26, 2018 at 10:30:34AM +0800, Phil Reid wrote:
>> On 26/09/2018 9:49 AM, Song Qiang wrote:
>>> On Tue, Sep 25, 2018 at 10:36:54PM +0800, Phil Reid wrote:
>>>> On 25/09/2018 9:30 PM, Jonathan Cameron wrote:
>>>>>> +static irqreturn_t rm3100_trigger_handler(int irq, void *p)
>>>>>> +{
>>>>>> +	struct iio_poll_func *pf = p;
>>>>>> +	struct iio_dev *indio_dev = pf->indio_dev;
>>>>>> +	struct rm3100_data *data = iio_priv(indio_dev);
>>>>>> +	struct regmap *regmap = data->regmap;
>>>>>> +	u8 buffer[9];
>>>>>> +	int ret;
>>>>>> +	int i;
>>>>>> +
>>>>>> +	mutex_lock(&data->lock);
>>>>>> +	ret = rm3100_wait_measurement(data);
>>>>>> +	if (ret < 0) {
>>>>>> +		mutex_unlock(&data->lock);
>>>>>> +		goto done;
>>>>>> +	}
>>>>>> +
>>>>>> +	ret = regmap_bulk_read(regmap, RM3100_REG_MX2, buffer, sizeof(buffer));
>>>>>> +	mutex_unlock(&data->lock);
>>>>>> +	if (ret < 0)
>>>>>> +		goto done;
>>>>>> +
>>>>>> +	/* Convert XXXYYYZZZxxx to XXXxYYYxZZZx. x for padding. */
>>>>>> +	for (i = 0; i < 3; i++)
>>>>>> +		memcpy(data->buffer + i * 4, buffer + i * 3, 3);
>>>>> Firstly X doesn't need copying.
>>>>> Secondly the copy of Y actually overwrites the value of Z
>>>>> XXXYYYZZZxxx
>>>>> XXXxYYYZZxxx
>>>>> XXXxYYYxYZZx
>>>>>
>>>>> I think...
>>>>>
>>>>>> +
>>>>>> +	iio_push_to_buffers_with_timestamp(indio_dev, data->buffer,
>>>>>> +			iio_get_time_ns(indio_dev));
>>>>
>>>> memcpy target is a different buffer so should be ok.
>>>>
>>>> But that raises the question of does it need to be?
>>>> 'buffer' could be 12 bytes long and just shuffle Z then Y.
>>>> Do the unused bytes need to be zeroed? or does libiio mask them anyway?
>>>>
>>>>
>>>>
>>>> -- 
>>>> Regards
>>>> Phil Reid
>>>
>>> Hi Phil,
>>>
>>> This is interesting, last patch I submitted uses three transactions and
>>> shuffles X, Y and Z respectively. You said it should be better to use one
>>> transactions, I thought it makes point, and one transaction may reduce
>>> IO pressure of the i2c bus. :)
>>> And that's not necessary for unused bytes to be zero. I'm not familiar
>>> with libiio, actually just been studying it, can't say anything about
>>> it.
>>>
>>> yours,
>>> Song Qiang
>>>
>>>
>> G'day Song,
>>
>> yes the one transaction suggestion was to reduce pressure on the bus.
>> I think also with 3 calls you can up up with other devices taking over
>> the i2c / spi bus in between.
>>
>> We've got a devkit for this part, but haven't got to wiring it up to our system as yet.
>> We're looking at using the i2c interface which could push things at max samplerate, so yes I'm
>> keen to see bus pressure reduced as much as possible.
>>
>> I was thinking something like the following:
>>
>> u8 buffer[12];
>> regmap_bulk_read(regmap, RM3100_REG_MX2, buffer, 9);
>>
>> buffer[10] = buffer[8]; // or memcpy or some other fancy shuffle code.
>> buffer[9]  = buffer[7];
>> buffer[8]  = buffer[6];
>>
>> buffer[6]  = buffer[5];
>> buffer[5]  = buffer[4];
>> buffer[4]  = buffer[3];
>>
>> iio_push_to_buffers_with_timestamp(indio_dev, buffer, iio_get_time_ns(indio_dev));
>>
>> but I'm unsure if this would be needed:
>> buffer[7] = 0
>> buffer[3] = 0
>>
>> What you've got does the job I think.
>>
>> I haven't dug into the datasheet in great detail, and my iio knownledge is limited.
>> Are you sure the RM3100_CHANNEL scantype endianness is IIO_LE.
>> rm3100_read_mag looks to be doing big endian conversion and the datasheet agrees with that.
>>
>>
>> -- 
>> Regards
>> Phil Reid
>>
> 
> Hi Phil,
> 
> You're absolutely right!
> This should be big endian, I think I probably just want something there
> when I was writing this code, planned to change it later, but apparently
> I've forgotten it...
> 
> AFAIK, filling places we do not need with 0 is not needed, we just
> extract valid data from valid bit field(24 here).
> 
> Both one transaction and three transactions way have their point, but
> this is a OS, probably the spiltted one is better, I need some real
> thinking about this...
The one transaction is better.
Reduces i2c traffic by 6 bytes and ensure the measurements are tightly
coupled in time for the 3 axis.

> 
> I could have use the same buffer to read from the sensor and send it to
> userspace like this:
> 
> int i = 0;
> ret = regmap_bulk_read(regmap, RM3100_REG_MX2, 9);
> if(ret)
> 	...
> /* Convert XXXYYYZZZxxx to XXXxYYYxZZZx. */
> for (i = 0; i < 2; i++)
> 	memcpy(buffer + (2 - i) * 4, buffer + (2 - i) * 3), 3);
> 
> This code snippet will use the same buffer, actually that's what I was
> using the first time. Jonathan must thinks so, from what he commented,
> he assumed I was using the same buffer, also what you want.
> But I changed this due to Peter's comment, maybe not a big deal, he
> suggests to use sizeof(buffer), this makes me use an additional size 9
> buffer. I thought this doesn't matter too much, just some additional
> space from the stack, but now I think maybe less memory using would be
> better...
> After all, this length 9 seems like never shouldn't be changed...

yes that does the job.

On Wed, 26 Sep 2018 16:09:45 +0800
Song Qiang <songqiang1304521@gmail.com> wrote:

> On Wed, Sep 26, 2018 at 10:30:34AM +0800, Phil Reid wrote:
> > On 26/09/2018 9:49 AM, Song Qiang wrote:  
> > > On Tue, Sep 25, 2018 at 10:36:54PM +0800, Phil Reid wrote:  
> > > > On 25/09/2018 9:30 PM, Jonathan Cameron wrote:  
> > > > > > +static irqreturn_t rm3100_trigger_handler(int irq, void *p)
> > > > > > +{
> > > > > > +	struct iio_poll_func *pf = p;
> > > > > > +	struct iio_dev *indio_dev = pf->indio_dev;
> > > > > > +	struct rm3100_data *data = iio_priv(indio_dev);
> > > > > > +	struct regmap *regmap = data->regmap;
> > > > > > +	u8 buffer[9];
> > > > > > +	int ret;
> > > > > > +	int i;
> > > > > > +
> > > > > > +	mutex_lock(&data->lock);
> > > > > > +	ret = rm3100_wait_measurement(data);
> > > > > > +	if (ret < 0) {
> > > > > > +		mutex_unlock(&data->lock);
> > > > > > +		goto done;
> > > > > > +	}
> > > > > > +
> > > > > > +	ret = regmap_bulk_read(regmap, RM3100_REG_MX2, buffer, sizeof(buffer));
> > > > > > +	mutex_unlock(&data->lock);
> > > > > > +	if (ret < 0)
> > > > > > +		goto done;
> > > > > > +
> > > > > > +	/* Convert XXXYYYZZZxxx to XXXxYYYxZZZx. x for padding. */
> > > > > > +	for (i = 0; i < 3; i++)
> > > > > > +		memcpy(data->buffer + i * 4, buffer + i * 3, 3);  
> > > > > Firstly X doesn't need copying.
> > > > > Secondly the copy of Y actually overwrites the value of Z
> > > > > XXXYYYZZZxxx
> > > > > XXXxYYYZZxxx
> > > > > XXXxYYYxYZZx
> > > > > 
> > > > > I think...
> > > > >   
> > > > > > +
> > > > > > +	iio_push_to_buffers_with_timestamp(indio_dev, data->buffer,
> > > > > > +			iio_get_time_ns(indio_dev));  
> > > > 
> > > > memcpy target is a different buffer so should be ok.
> > > > 
> > > > But that raises the question of does it need to be?
> > > > 'buffer' could be 12 bytes long and just shuffle Z then Y.
> > > > Do the unused bytes need to be zeroed? or does libiio mask them anyway?
> > > > 
> > > > 
> > > > 
> > > > -- 
> > > > Regards
> > > > Phil Reid  
> > > 
> > > Hi Phil,
> > > 
> > > This is interesting, last patch I submitted uses three transactions and
> > > shuffles X, Y and Z respectively. You said it should be better to use one
> > > transactions, I thought it makes point, and one transaction may reduce
> > > IO pressure of the i2c bus. :)
> > > And that's not necessary for unused bytes to be zero. I'm not familiar
> > > with libiio, actually just been studying it, can't say anything about
> > > it.
> > > 
> > > yours,
> > > Song Qiang
> > > 
> > >   
> > G'day Song,
> > 
> > yes the one transaction suggestion was to reduce pressure on the bus.
> > I think also with 3 calls you can up up with other devices taking over
> > the i2c / spi bus in between.
> > 
> > We've got a devkit for this part, but haven't got to wiring it up to our system as yet.
> > We're looking at using the i2c interface which could push things at max samplerate, so yes I'm
> > keen to see bus pressure reduced as much as possible.
> > 
> > I was thinking something like the following:
> > 
> > u8 buffer[12];
> > regmap_bulk_read(regmap, RM3100_REG_MX2, buffer, 9);
> > 
> > buffer[10] = buffer[8]; // or memcpy or some other fancy shuffle code.
> > buffer[9]  = buffer[7];
> > buffer[8]  = buffer[6];
> > 
> > buffer[6]  = buffer[5];
> > buffer[5]  = buffer[4];
> > buffer[4]  = buffer[3];
> > 
> > iio_push_to_buffers_with_timestamp(indio_dev, buffer, iio_get_time_ns(indio_dev));
> > 
> > but I'm unsure if this would be needed:
> > buffer[7] = 0
> > buffer[3] = 0
> > 
> > What you've got does the job I think.
> > 
> > I haven't dug into the datasheet in great detail, and my iio knownledge is limited.
> > Are you sure the RM3100_CHANNEL scantype endianness is IIO_LE.
> > rm3100_read_mag looks to be doing big endian conversion and the datasheet agrees with that.
> > 
> > 
> > -- 
> > Regards
> > Phil Reid
> >   
> 
> Hi Phil,
> 
> You're absolutely right!
> This should be big endian, I think I probably just want something there
> when I was writing this code, planned to change it later, but apparently
> I've forgotten it...
> 
> AFAIK, filling places we do not need with 0 is not needed, we just
> extract valid data from valid bit field(24 here).
Indeed it isn't.  We need to be careful not to leak any data (for
kernel security reasons), but it's fine if it just has some other
data from the sensor in it.
> 
> Both one transaction and three transactions way have their point, but
> this is a OS, probably the spiltted one is better, I need some real
> thinking about this...
> 
> I could have use the same buffer to read from the sensor and send it to
> userspace like this:
> 
> int i = 0;
> ret = regmap_bulk_read(regmap, RM3100_REG_MX2, 9);
> if(ret)
> 	...
> /* Convert XXXYYYZZZxxx to XXXxYYYxZZZx. */
> for (i = 0; i < 2; i++)
> 	memcpy(buffer + (2 - i) * 4, buffer + (2 - i) * 3), 3);
> 
> This code snippet will use the same buffer, actually that's what I was
> using the first time. Jonathan must thinks so, from what he commented,
> he assumed I was using the same buffer, also what you want.

Gah. Good point!  Two things called buffer and I failed to notice they
were different. :(

> But I changed this due to Peter's comment, maybe not a big deal, he
> suggests to use sizeof(buffer), this makes me use an additional size 9
> buffer. I thought this doesn't matter too much, just some additional
> space from the stack, but now I think maybe less memory using would be
> better...
> After all, this length 9 seems like never shouldn't be changed...

Agreed. Here in place is simple, avoids memory usage and also one of the
copies.

Jonathan

> 
> yours,
> Song Qiang
>

On Wed, 26 Sep 2018 09:33:53 +0800
Song Qiang <songqiang1304521@gmail.com> wrote:

> On Tue, Sep 25, 2018 at 02:30:54PM +0100, Jonathan Cameron wrote:
> > On Tue, 25 Sep 2018 11:17:24 +0800
> > Song Qiang <songqiang1304521@gmail.com> wrote:
> >   
> > > PNI RM3100 is a high resolution, large signal immunity magnetometer,
> > > composed of 3 single sensors and a processing chip with MagI2C Interface.
> > > 
> > > Following functions are available:
> > > - Single-shot measurement from
> > >   /sys/bus/iio/devices/iio:deviceX/in_magn_{axis}_raw
> > > - Triggerd buffer measurement.
> > > - Both i2c and spi interface are supported.
> > > - Both interrupt and polling measurement is supported, depands on if
> > >   the 'interrupts' in DT is declared.
> > > 
> > > Signed-off-by: Song Qiang <songqiang1304521@gmail.com>  
> > Various minor comments inline.  Definitely heading in the right direction.
> > 
> > Good work.
> > 
> > Thanks,
> > 
> > Jonathan
> >   
> 
> ...
> 
> > > +static int rm3100_get_samp_freq(struct rm3100_data *data, int *val, int *val2)
> > > +{
> > > +	int ret;
> > > +	int tmp;
> > > +
> > > +	mutex_lock(&data->lock);
> > > +	ret = regmap_read(data->regmap, RM3100_REG_TMRC, &tmp);
> > > +	mutex_unlock(&data->lock);
> > > +	if (ret < 0)
> > > +		return ret;
> > > +	*val = rm3100_samp_rates[tmp - RM3100_TMRC_OFFSET][0];
> > > +	*val2 = rm3100_samp_rates[tmp - RM3100_TMRC_OFFSET][1];
> > > +
> > > +	return IIO_VAL_INT_PLUS_MICRO;
> > > +}
> > > +
> > > +static int rm3100_set_cycle_count(struct rm3100_data *data, int val)
> > > +{
> > > +	int ret;
> > > +	u8 i;
> > > +
> > > +	for (i = 0; i < 3; i++) {
> > > +		ret = regmap_write(data->regmap, RM3100_REG_CC_X + 2 * i, 100);  
> > 
> > Does this write it to the same value irrespective of the value of val?
> > Seems odd.
> >   
> Hi Jonathan,
> 
> Sometimes I see these mistakes I couldn't stop laughing at my stupiness.
> Should be val, my mistake submitting without a throughout functional
> check, I think I'll write a script to prevent this from happening again.
Not to worry, we all do it :)  I had a good half day this week failing to
spot a really dumb buffer overrun (was evil as it was actually writing
a copy to memory that by coincidence was always just before where it
was being copied from so looked like a shift in the second array - hence
hours of looking in completely the wrong place).  

Sadly, for an individual developer tests always tend to be a bit adhoc
and sometimes we simply forget one!

> 
> > > +		if (ret < 0)
> > > +			return ret;
> > > +	}
> > > +	if (val == 50)  
> > 
> > Switch would be nicer.  Also why have all other values call back to
> > 2 rather than generating an error?
> >   
> I could have given it an error path, but I checked the code, 'val' in
> this function is always given by my code. I think this leads no
> possibility for val to go wrong. Do I still need an error path in this
> circumstance?

With a switch you will to make the static checkers happy.  Put
a comment in there saying it won't happen.

> 
> > > +		data->cycle_count_index = 0;
> > > +	else if (val == 100)
> > > +		data->cycle_count_index = 1;
> > > +	else
> > > +		data->cycle_count_index = 2;
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +static int rm3100_set_samp_freq(struct rm3100_data *data, int val, int val2)
> > > +{
> > > +	struct regmap *regmap = data->regmap;
> > > +	int cycle_count;
> > > +	int ret;
> > > +	int i;
> > > +
> > > +	mutex_lock(&data->lock);  
> > 
> > Why are you taking this lock? It's not well documented what it protects
> > so it's not clear in this path why it is taken.
> > (hint add a comment to the definition of the lock to make it clear!)
> > - note I'm not saying it shouldn't be taken here, just that there is no
> > comment to justify it..
> >   
> When I was considering the lock, I read Robert Love's 'Linux Kernel
> Development', whose chapter 9 talks about how to understand the lock.
> It was talking about protecting data, but in here, my purpose is to
> protect the i2c execution consistency. I think it may be possible that
> one person is extracting the data while another person is planning set
> the frequency. Setting the frequency within queuing data will causing
> CMM(Continuous Measurement Mode) register reset, breaking the measurement
> process. That's why I added lock to callbacks where a i2c sequence can
> happen. I referred code from hmc5843, which did the similar lock stuff,
> am I understanding about lock right?

The use of lock is fine.  Just needs documenting in the driver so that
other people can follow your logic in the future!
All locks should have a clear definition of purpose and scope.

> 
> > > +	/* All cycle count registers use the same value. */
> > > +	ret = regmap_read(regmap, RM3100_REG_CC_X, &cycle_count);
> > > +	if (ret < 0)
> > > +		goto unlock_return;
> > > +
> > > +	for (i = 0; i < RM3100_SAMP_NUM; i++) {
> > > +		if (val == rm3100_samp_rates[i][0] &&
> > > +		    val2 == rm3100_samp_rates[i][1])
> > > +			break;
> > > +	}
> > > +	if (i == RM3100_SAMP_NUM) {
> > > +		ret = -EINVAL;
> > > +		goto unlock_return;
> > > +	}
> > > +
> > > +	ret = regmap_write(regmap, RM3100_REG_TMRC, i + RM3100_TMRC_OFFSET);
> > > +	if (ret < 0)
> > > +		goto unlock_return;  
> 
> ...
> 
> > > +	if (ret < 0)
> > > +		goto done;
> > > +
> > > +	/* Convert XXXYYYZZZxxx to XXXxYYYxZZZx. x for padding. */
> > > +	for (i = 0; i < 3; i++)
> > > +		memcpy(data->buffer + i * 4, buffer + i * 3, 3);  
> > 
> > Firstly X doesn't need copying.
> > Secondly the copy of Y actually overwrites the value of Z
> > XXXYYYZZZxxx
> > XXXxYYYZZxxx
> > XXXxYYYxYZZx
> > 
> > I think...
> >   
> They are in different memories, buffer is a temporary memory for data
> reading out, data->buffer is for pushing to the userspace.

Yes. Stupid misread from me! Sorry about that.

> 
> > > +
> > > +	iio_push_to_buffers_with_timestamp(indio_dev, data->buffer,
> > > +			iio_get_time_ns(indio_dev));  
> > 
> > Align with opening bracket. 
> >   
> > > +
> > > +done:
> > > +	iio_trigger_notify_done(indio_dev->trig);
> > > +
> > > +	return IRQ_HANDLED;
> > > +}
> > > +
> > > +static void rm3100_remove(void *dh)
> > > +{
> > > +	struct rm3100_data *data = (struct rm3100_data *)dh;
> > > +	int ret;
> > > +
> > > +	ret = regmap_write(data->regmap, RM3100_REG_CMM, 0x00);
> > > +	if (ret < 0)
> > > +		dev_err(data->dev, "failed to stop device.\n");
> > > +}
> > > +
> > > +int rm3100_common_probe(struct device *dev, struct regmap *regmap, int irq)
> > > +{
> > > +	struct iio_dev *indio_dev;
> > > +	struct rm3100_data *data;
> > > +	int tmp;
> > > +	int ret;
> > > +
> > > +	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
> > > +	if (!indio_dev)
> > > +		return -ENOMEM;
> > > +
> > > +	data = iio_priv(indio_dev);
> > > +	data->dev = dev;
> > > +	data->regmap = regmap;
> > > +	data->buffer = devm_kzalloc(dev, RM3100_SCAN_BYTES, GFP_KERNEL);
> > > +	if (!data->buffer)
> > > +		return -ENOMEM;
> > > +
> > > +	mutex_init(&data->lock);
> > > +
> > > +	indio_dev->dev.parent = dev;
> > > +	indio_dev->name = "rm3100";
> > > +	indio_dev->info = &rm3100_info;
> > > +	indio_dev->channels = rm3100_channels;
> > > +	indio_dev->num_channels = ARRAY_SIZE(rm3100_channels);
> > > +	indio_dev->modes = INDIO_DIRECT_MODE;
> > > +	indio_dev->available_scan_masks = rm3100_scan_masks;
> > > +
> > > +	if (!irq)
> > > +		data->use_interrupt = false;
> > > +	else {
> > > +		data->use_interrupt = true;
> > > +		ret = devm_request_irq(dev,
> > > +				       irq,
> > > +				       rm3100_irq_handler,
> > > +				       IRQF_TRIGGER_RISING,
> > > +				       indio_dev->name,
> > > +				       data);
> > > +		if (ret < 0) {
> > > +			dev_err(dev, "request irq line failed.\n");
> > > +			return ret;
> > > +		}
> > > +		init_completion(&data->measuring_done);
> > > +	}
> > > +
> > > +	ret = devm_iio_triggered_buffer_setup(dev, indio_dev, NULL,
> > > +					      rm3100_trigger_handler, NULL);
> > > +	if (ret < 0)
> > > +		return ret;
> > > +
> > > +	/* 3sec more wait time. */  
> > 
> > I have no idea what this comment is referring to..
> > Not seeing any waiting here...
> >   
> The thing is, measurement time of this sensor span from ~1.7ms to ~13
> seconds. I'll need a wait time for *_wait_measurement(), and I use
> measurement time + 3 seconds for waiting time. This is an initialization.
> Usage of this is in *_wait_measurement.

The wait comment is fine, but why here? It seemed to be floating on it's
own.

> 
> yours,
> Song Qiang
> 
> > > +	ret = regmap_read(regmap, RM3100_REG_TMRC, &tmp);
> > > +	if (ret < 0)
> > > +		return ret;
> > > +	data->conversion_time =
> > > +		rm3100_samp_rates[tmp-RM3100_TMRC_OFFSET][2] + 3000;  
> > 
> > spacing around -  
> > Please check this throughout.  
> 
> ...