[2/2] add w1_ds28e17 driver for the DS28E17 Onewire to I2C master bridge

Message ID 578A95E4.1080903@gmx.de
State Superseded
Headers show

Commit Message

Jan Kandziora July 16, 2016, 8:15 p.m.
This subpatch adds a driver for the DS28E17 Onewire to I2C master bridge.

Signed-off-by: Jan Kandziora <jjj@gmx.de>
---
 drivers/w1/slaves/Kconfig      |  19 +
 drivers/w1/slaves/Makefile     |   1 +
 drivers/w1/slaves/w1_ds28e17.c | 761 +++++++++++++++++++++++++++++++++++++++++
 drivers/w1/w1_family.h         |   1 +
 4 files changed, 782 insertions(+)
 create mode 100644 drivers/w1/slaves/w1_ds28e17.c

Comments

Evgeniy Polyakov July 20, 2016, 5:34 p.m. | #1
Hi Jan

16.07.2016, 23:15, "Jan Kandziora" <jjj@gmx.de>:
> This subpatch adds a driver for the DS28E17 Onewire to I2C master bridge.
>
> Signed-off-by: Jan Kandziora <jjj@gmx.de>

Both patches look good to me, I ack and recommend them for inclusion.
There is a tiny typo and a bit general question below.

Acked-by: Evgeniy Polyakov <zbr@ioremap.net>

> +/* Contants for calculating the busy sleep. */

It should be 'constants' I suppose

> +/* Wait a while until the busy flag clears. */
> +static int w1_f19_i2c_busy_wait(struct w1_slave *sl, size_t count)
> +{
> + const unsigned long timebases[3] = W1_F19_BUSY_TIMEBASES;
> + struct w1_f19_data *data = sl->family_data;
> + unsigned int checks;
> +
> + /* Check the busy flag first in any case.*/
> + if (w1_touch_bit(sl->master, 1) == 0)
> + return 0;
> +
> + /*
> + * Do a generously long sleep in the beginning,
> + * as we have to wait at least this time for all
> + * the I2C bytes at the given speed to be transferred.
> + */
> + usleep_range(timebases[data->speed] * (data->stretch) * count,
> + timebases[data->speed] * (data->stretch) * count
> + + W1_F19_BUSY_GRATUITY);
> +
> + /* Now continusly check the busy flag sent by the DS28E17. */
> + checks = W1_F19_BUSY_CHECKS;
> + while ((checks--) > 0) {

This will burn CPU for 1000 cycles of timebase[data->speed] useconds.
Is that a hardware limitation that there is no interrupt or other completion mechanism which would handle this case?

> + /* Return success if the busy flag is cleared. */
> + if (w1_touch_bit(sl->master, 1) == 0)
> + return 0;
> +
> + /* Wait one non-streched byte timeslot. */
> + udelay(timebases[data->speed]);
> + }
> +
> + /* Timeout. */
> + dev_warn(&sl->dev, "busy timeout\n");
> + return -EIO;
> +}
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Jan Kandziora July 20, 2016, 6:01 p.m. | #2
Am 20.07.2016 um 19:34 schrieb Evgeniy Polyakov:
> Hi Jan
> 
> 16.07.2016, 23:15, "Jan Kandziora" <jjj@gmx.de>:
>> This subpatch adds a driver for the DS28E17 Onewire to I2C master bridge.
>>
>> Signed-off-by: Jan Kandziora <jjj@gmx.de>
> 
> Both patches look good to me, I ack and recommend them for inclusion.
> There is a tiny typo and a bit general question below.
> 
> Acked-by: Evgeniy Polyakov <zbr@ioremap.net>
> 
>> +/* Contants for calculating the busy sleep. */
> 
> It should be 'constants' I suppose
> 
Sure. [^_^;]


>> +/* Wait a while until the busy flag clears. */
>> +static int w1_f19_i2c_busy_wait(struct w1_slave *sl, size_t count)
>> +{
>> + const unsigned long timebases[3] = W1_F19_BUSY_TIMEBASES;
>> + struct w1_f19_data *data = sl->family_data;
>> + unsigned int checks;
>> +
>> + /* Check the busy flag first in any case.*/
>> + if (w1_touch_bit(sl->master, 1) == 0)
>> + return 0;
>> +
>> + /*
>> + * Do a generously long sleep in the beginning,
>> + * as we have to wait at least this time for all
>> + * the I2C bytes at the given speed to be transferred.
>> + */
>> + usleep_range(timebases[data->speed] * (data->stretch) * count,
>> + timebases[data->speed] * (data->stretch) * count
>> + + W1_F19_BUSY_GRATUITY);
>> +
>> + /* Now continusly check the busy flag sent by the DS28E17. */
>> + checks = W1_F19_BUSY_CHECKS;
>> + while ((checks--) > 0) {
> 
> This will burn CPU for 1000 cycles of timebase[data->speed] useconds.
> Is that a hardware limitation that there is no interrupt or other completion mechanism which would handle this case?
> 
The main completion mechanism is usleep_range() above. It suspends the
execution for at least as long as the DS28E17 I2C operation takes. This
is calculated from the transfer speed and the number of bytes transferred.

After that, the driver checks for the busy flag actively. It does so
because the I2C slave device may have used clock stretching. There is
that "stretch" parameter but we need some measure of last resort.


>> + /* Return success if the busy flag is cleared. */
>> + if (w1_touch_bit(sl->master, 1) == 0)
>> + return 0;
>
This check will usually succeed on first test, given the I2C slave
device hasn't used any clock stretching.

I've set the loop limit as high as 1000 to avoid "busy timeouts". We
could set it to 10, then watch which I2C slave devices produce fallout.
Could be interesting.

I even thought about putting in a "stretch" array to make the timeout
calculation configureable per I2C slave. Then I realized no one would
ever use that feature because the most likely configuration is to have
one I2C slave device on one DS28E17.


>> +
>> + /* Wait one non-streched byte timeslot. */
>> + udelay(timebases[data->speed]);
>> + }
>> +
>> + /* Timeout. */
>> + dev_warn(&sl->dev, "busy timeout\n");
>> + return -EIO;
>> +}
> 

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Jan Kandziora July 20, 2016, 6:19 p.m. | #3
Am 20.07.2016 um 19:34 schrieb Evgeniy Polyakov:
> 
> Is that a hardware limitation that there is no interrupt or other
> completion mechanism which would handle this case?
> 
Ah, forgot to address that question.

The DS28E17 has a BUSY pin. We could add an interrupt-driven busy
mechanism but the mechanism without the interrupt line has to stay in
there because most people wouldn't add an interrupt line to their
Onewire installation just for having that.

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Wolfram Sang July 21, 2016, 7:02 a.m. | #4
On Sat, Jul 16, 2016 at 10:15:32PM +0200, Jan Kandziora wrote:
> This subpatch adds a driver for the DS28E17 Onewire to I2C master bridge.
> 
> Signed-off-by: Jan Kandziora <jjj@gmx.de>

Thanks for the submission.

> +config W1_SLAVE_DS28E17
> +	tristate "1-wire-to-I2C master bridge (DS28E17)"
> +	select CRC16
> +	depends on I2C
> +	help
> +	  Say Y here if you want to use the DS28E17 1-wire-to-I2C master bridge.
> +	  For each DS28E17 detected, a new I2C adapter is created within the
> +	  kernel. I2C devices on that bus can be configured to be used by the
> +	  kernel as on any other "native" I2C bus.
> +
> +	  In addition, that new I2C bus is accessible from userspace through
> +	  a /dev/i2c-nnn device node if you have enabled
> +	  "Device Drivers->I2C Support->I2C device interface" (CONFIG_I2C_CHARDEV).

I think the last paragraph can go. This is standard I2C behaviour and
Kconfig is not the right place to document this.


> --- /dev/null
> +++ b/drivers/w1/slaves/w1_ds28e17.c
> @@ -0,0 +1,761 @@
> +/*
> + *	w1_ds28e17.c - w1 family 19 (DS28E17) driver
> + *
> + * Copyright (c) 2016 Jan Kandziora <jjj@gmx.de>
> + *
> + * This source code is licensed under the GNU General Public License,
> + * Version 2. See the file COPYING for more details.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/moduleparam.h>
> +#include <linux/device.h>
> +#include <linux/types.h>
> +#include <linux/delay.h>
> +#include <linux/slab.h>
> +#include <linux/crc16.h>
> +#include <linux/uaccess.h>
> +#include <linux/i2c.h>

If you sort these, it is easier to avoid duplicates later.

> +
> +#define CRC16_INIT 0
> +
> +#include "../w1.h"
> +#include "../w1_int.h"
> +#include "../w1_family.h"
> +
> +
> +/* Module setup. */
> +MODULE_LICENSE("GPL");

"GPL v2"

> +MODULE_AUTHOR("Jan Kandziora <jjj@gmx.de>");
> +MODULE_DESCRIPTION("w1 family 19 driver for DS28E17, 1-wire to I2C master bridge");
> +MODULE_ALIAS("w1-family-" __stringify(W1_FAMILY_DS28E17));
> +
> +
> +/* Default I2C speed to be set when a DS28E17 is detected. */
> +static char i2c_speed = 1;
> +module_param_named(speed, i2c_speed, byte, (S_IRUSR | S_IWUSR));
> +MODULE_PARM_DESC(speed, "Default I2C speed to be set when a DS28E17 is detected");

I don't see any documentation what 0,1,2 means. I think it would be more
user friendly to actually use the kHz values here.


> +/* Default I2C stretch value to be set when a DS28E17 is detected. */
> +static char i2c_stretch = 1;
> +module_param_named(stretch, i2c_stretch, byte, (S_IRUSR | S_IWUSR));
> +MODULE_PARM_DESC(stretch, "Default I2C stretch value to be set when a DS28E17 is detected");

No documentation what the value means.

> +/* DS28E17 device command codes. */
> +#define W1_F19_WRITE_DATA_WITH_STOP      0x4B
> +#define W1_F19_WRITE_DATA_NO_STOP        0x5A
> +#define W1_F19_WRITE_DATA_ONLY           0x69
> +#define W1_F19_WRITE_DATA_ONLY_WITH_STOP 0x78
> +#define W1_F19_READ_DATA_WITH_STOP       0x87
> +#define W1_F19_WRITE_READ_DATA_WITH_STOP 0x2D
> +#define W1_F19_WRITE_CONFIGURATION       0xD2
> +#define W1_F19_READ_CONFIGURATION        0xE1
> +#define W1_F19_ENABLE_SLEEP_MODE         0x1E
> +#define W1_F19_READ_DEVICE_REVISION      0xC4
> +
> +/* DS28E17 status bits */
> +#define W1_F19_STATUS_CRC     0x01
> +#define W1_F19_STATUS_ADDRESS 0x02
> +#define W1_F19_STATUS_START   0x08
> +
> +/*
> + * Maximum number of I2C bytes to transfer within one CRC16 protected onewire
> + * command.
> + * */
> +#define W1_F19_WRITE_DATA_LIMIT 255
> +
> +/* Maximum number of I2C bytes to read with one onewire command. */
> +#define W1_F19_READ_DATA_LIMIT 255
> +
> +/* Contants for calculating the busy sleep. */
> +#define W1_F19_BUSY_TIMEBASES { 90, 23, 10 }
> +#define W1_F19_BUSY_GRATUITY  1000
> +
> +/* Number of checks for the busy flag before timeout. */
> +#define W1_F19_BUSY_CHECKS 1000
> +
> +
> +/* Slave specific data. */
> +struct w1_f19_data {
> +	u8 speed;
> +	u8 stretch;
> +	struct i2c_adapter adapter;
> +};
> +
> +
> +/* Wait a while until the busy flag clears. */
> +static int w1_f19_i2c_busy_wait(struct w1_slave *sl, size_t count)
> +{
> +	const unsigned long timebases[3] = W1_F19_BUSY_TIMEBASES;
> +	struct w1_f19_data *data = sl->family_data;
> +	unsigned int checks;
> +
> +	/* Check the busy flag first in any case.*/
> +	if (w1_touch_bit(sl->master, 1) == 0)
> +		return 0;
> +
> +	/*
> +	 * Do a generously long sleep in the beginning,
> +	 * as we have to wait at least this time for all
> +	 * the I2C bytes at the given speed to be transferred.
> +	 */
> +	usleep_range(timebases[data->speed] * (data->stretch) * count,
> +		timebases[data->speed] * (data->stretch) * count
> +		+ W1_F19_BUSY_GRATUITY);
> +
> +	/* Now continusly check the busy flag sent by the DS28E17. */
> +	checks = W1_F19_BUSY_CHECKS;
> +	while ((checks--) > 0) {
> +		/* Return success if the busy flag is cleared. */
> +		if (w1_touch_bit(sl->master, 1) == 0)
> +			return 0;
> +
> +		/* Wait one non-streched byte timeslot. */
> +		udelay(timebases[data->speed]);
> +	}
> +
> +	/* Timeout. */
> +	dev_warn(&sl->dev, "busy timeout\n");
> +	return -EIO;
> +}
> +
> +
> +/* Utility function: write data to I2C slave, single chunk. */
> +static int __w1_f19_i2c_write(struct w1_slave *sl,
> +	const u8 *command, size_t command_count,
> +	const u8 *buffer, size_t count)
> +{
> +	u16 crc;
> +	u8 w1_buf[2];
> +
> +	/* Send command and I2C data to DS28E17. */
> +	crc = crc16(CRC16_INIT, command, command_count);
> +	w1_write_block(sl->master, command, command_count);
> +
> +	w1_buf[0] = count;
> +	crc = crc16(crc, w1_buf, 1);
> +	w1_write_8(sl->master, w1_buf[0]);
> +
> +	crc = crc16(crc, buffer, count);
> +	w1_write_block(sl->master, buffer, count);
> +
> +	w1_buf[0] = ~(crc & 0xFF);
> +	w1_buf[1] = ~((crc >> 8) & 0xFF);
> +	w1_write_block(sl->master, w1_buf, 2);
> +
> +	/* Wait until busy flag clears (or timeout). */
> +	if (w1_f19_i2c_busy_wait(sl, count + 1) < 0)
> +		return -EIO;
> +
> +	/* Read status from DS28E17. */
> +	w1_read_block(sl->master, w1_buf, 2);
> +
> +	/* Warnings. */
> +	if (w1_buf[0] & W1_F19_STATUS_CRC)
> +		dev_warn(&sl->dev, "crc16 mismatch\n");
> +	if (w1_buf[0] & W1_F19_STATUS_ADDRESS)
> +		dev_warn(&sl->dev, "i2c device not responding\n");

This should ideally return -ENXIO.

> +	if (w1_buf[0] & W1_F19_STATUS_START)
> +		dev_warn(&sl->dev, "i2c start condition invalid\n");

Does that mean "arbitration lost"? Then it should return "-EAGAIN".

> +	if ((w1_buf[0] & (W1_F19_STATUS_CRC | W1_F19_STATUS_ADDRESS)) == 0
> +			&& w1_buf[1] != 0) {
> +		dev_warn(&sl->dev, "i2c short write, %d bytes not acknowledged\n",
> +			w1_buf[1]);
> +	}
> +
> +	/* Check error conditions. */
> +	if (w1_buf[0] != 0 || w1_buf[1] != 0)
> +		return -EIO;
> +
> +	/* All ok. */
> +	return count;
> +}
> +
> +
> +/* Write data to I2C slave. */
> +static int w1_f19_i2c_write(struct w1_slave *sl, u16 i2c_address,
> +	const u8 *buffer, size_t count, bool stop)
> +{
> +	int result;
> +	int remaining = count;
> +	const u8 *p;
> +	u8 command[2];
> +
> +	/* Check input. */
> +	if (i2c_address > 0x7F

The i2c core checks that for you.

> +			|| count == 0)

For that case, better return -EOPNOTSUPP;

> +		return 0;
> +
> +	/* Check whether we need multiple commands. */
> +	if (count <= W1_F19_WRITE_DATA_LIMIT) {
> +		/*
> +		 * Small data amount. Data can be sent with
> +		 * a single onewire command.
> +		 */
> +
> +		/* Send all data to DS28E17. */
> +		command[0] = (stop ? W1_F19_WRITE_DATA_WITH_STOP
> +			: W1_F19_WRITE_DATA_NO_STOP);
> +		command[1] = i2c_address << 1;
> +		result = __w1_f19_i2c_write(sl, command, 2, buffer, count);
> +	} else {
> +		/* Large data amount. Data has to be sent in multiple chunks. */
> +
> +		/* Send first chunk to DS28E17. */
> +		p = buffer;
> +		command[0] = W1_F19_WRITE_DATA_NO_STOP;
> +		command[1] = i2c_address << 1;
> +		result = __w1_f19_i2c_write(sl, command, 2, p,
> +			W1_F19_WRITE_DATA_LIMIT);
> +		if (result < 0)
> +			return result;
> +
> +		/* Resume to same DS28E17. */
> +		if (w1_reset_resume_command(sl->master))
> +			return -ENXIO;

-ENXIO? Please check Documentation/i2c/fault-codes if that fits

> +
> +		/* Next data chunk. */
> +		p += W1_F19_WRITE_DATA_LIMIT;
> +		remaining -= W1_F19_WRITE_DATA_LIMIT;
> +
> +		while (remaining > W1_F19_WRITE_DATA_LIMIT) {
> +			/* Send intermediate chunk to DS28E17. */
> +			command[0] = W1_F19_WRITE_DATA_ONLY;
> +			result = __w1_f19_i2c_write(sl, command, 1, p,
> +					W1_F19_WRITE_DATA_LIMIT);
> +			if (result < 0)
> +				return result;
> +
> +			/* Resume to same DS28E17. */
> +			if (w1_reset_resume_command(sl->master))
> +				return -ENXIO;
> +
> +			/* Next data chunk. */
> +			p += W1_F19_WRITE_DATA_LIMIT;
> +			remaining -= W1_F19_WRITE_DATA_LIMIT;
> +		}
> +
> +		/* Send final chunk to DS28E17. */
> +		command[0] = (stop ? W1_F19_WRITE_DATA_ONLY_WITH_STOP
> +			: W1_F19_WRITE_DATA_ONLY);
> +		result = __w1_f19_i2c_write(sl, command, 1, p, remaining);
> +	}
> +
> +	return result;
> +}
> +
> +
> +/* Read data from I2C slave. */
> +static int w1_f19_i2c_read(struct w1_slave *sl, u16 i2c_address,
> +	u8 *buffer, size_t count)
> +{
> +	u16 crc;
> +	u8 w1_buf[5];
> +
> +	/* Check input. */
> +	if (i2c_address > 0x7F
> +			|| count > W1_F19_READ_DATA_LIMIT

Since you have a quirk structure, the core checks this for you, too.

> +			|| count == 0)
> +		return -EINVAL;

-EOPNOTSUPP.

> +
> +	/* Send command to DS28E17. */
> +	w1_buf[0] = W1_F19_READ_DATA_WITH_STOP;
> +	w1_buf[1] = i2c_address << 1 | 0x01;
> +	w1_buf[2] = count;
> +	crc = crc16(CRC16_INIT, w1_buf, 3);
> +	w1_buf[3] = ~(crc & 0xFF);
> +	w1_buf[4] = ~((crc >> 8) & 0xFF);
> +	w1_write_block(sl->master, w1_buf, 5);
> +
> +	/* Wait until busy flag clears (or timeout). */
> +	if (w1_f19_i2c_busy_wait(sl, count + 1) < 0)
> +		return -EIO;
> +
> +	/* Read status from DS28E17. */
> +	w1_buf[0] = w1_read_8(sl->master);
> +
> +	/* Warnings. */
> +	if (w1_buf[0] & W1_F19_STATUS_CRC)
> +		dev_warn(&sl->dev, "crc16 mismatch\n");
> +	if (w1_buf[0] & W1_F19_STATUS_ADDRESS)
> +		dev_warn(&sl->dev, "i2c device not responding\n");
> +	if (w1_buf[0] & W1_F19_STATUS_START)
> +		dev_warn(&sl->dev, "i2c start condition invalid\n");

Same as above.

> +
> +	/* Check error conditions. */
> +	if (w1_buf[0] != 0)
> +		return -EIO;
> +
> +	/* Read received I2C data from DS28E17. */
> +	return w1_read_block(sl->master, buffer, count);
> +}
> +
> +
> +/* Write to, then read data from I2C slave. */
> +static int w1_f19_i2c_write_read(struct w1_slave *sl, u16 i2c_address,
> +	const u8 *wbuffer, size_t wcount, u8 *rbuffer, size_t rcount)
> +{
> +	u16 crc;
> +	u8 w1_buf[3];
> +
> +	/* Check input. */
> +	if (i2c_address > 0x7F
> +			|| wcount == 0
> +			|| rcount > W1_F19_READ_DATA_LIMIT
> +			|| rcount == 0)
> +		return -EINVAL;

Same comments as above

> +
> +	/* Send command and I2C data to DS28E17. */
> +	w1_buf[0] = W1_F19_WRITE_READ_DATA_WITH_STOP;
> +	w1_buf[1] = i2c_address << 1;
> +	w1_buf[2] = wcount;
> +	crc = crc16(CRC16_INIT, w1_buf, 3);
> +	w1_write_block(sl->master, w1_buf, 3);
> +
> +	crc = crc16(crc, wbuffer, wcount);
> +	w1_write_block(sl->master, wbuffer, wcount);
> +
> +	w1_buf[0] = rcount;
> +	crc = crc16(crc, w1_buf, 1);
> +	w1_buf[1] = ~(crc & 0xFF);
> +	w1_buf[2] = ~((crc >> 8) & 0xFF);
> +	w1_write_block(sl->master, w1_buf, 3);
> +
> +	/* Wait until busy flag clears (or timeout). */
> +	if (w1_f19_i2c_busy_wait(sl, wcount + rcount + 2) < 0)
> +		return -EIO;
> +
> +	/* Read status from DS28E17. */
> +	w1_read_block(sl->master, w1_buf, 2);
> +
> +	/* Warnings. */
> +	if (w1_buf[0] & W1_F19_STATUS_CRC)
> +		dev_warn(&sl->dev, "crc16 mismatch\n");
> +	if (w1_buf[0] & W1_F19_STATUS_ADDRESS)
> +		dev_warn(&sl->dev, "i2c device not responding\n");
> +	if (w1_buf[0] & W1_F19_STATUS_START)
> +		dev_warn(&sl->dev, "i2c start condition invalid\n");
> +	if ((w1_buf[0] & (W1_F19_STATUS_CRC | W1_F19_STATUS_ADDRESS)) == 0
> +			&& w1_buf[1] != 0) {
> +		dev_warn(&sl->dev, "i2c short write, %d bytes not acknowledged\n",
> +			w1_buf[1]);
> +	}
> +
> +	/* Check error conditions. */
> +	if (w1_buf[0] != 0 || w1_buf[1] != 0)
> +		return -EIO;

ditto. Maybe you should put this parsing into a seperate function?

> +
> +	/* Read received I2C data from DS28E17. */
> +	return w1_read_block(sl->master, rbuffer, rcount);
> +}
> +
> +
> +/* Do an I2C master transfer. */
> +static int w1_f19_i2c_master_transfer(struct i2c_adapter *adapter,
> +	struct i2c_msg *msgs, int num)
> +{
> +	struct w1_slave *sl = (struct w1_slave *) adapter->algo_data;
> +	int i = 0;
> +	int result = 0;
> +
> +	/* Return if no messages to send/receive. */
> +	if (num == 0)
> +		return 0;

Heh, I was about to write "the core will check this for you", but it
doesn't. I'll send a patch to fix that, thanks! So please remove it
here.

> +
> +	/* Start onewire transaction. */
> +	mutex_lock(&sl->master->bus_mutex);
> +
> +	/* Select DS28E17. */
> +	if (w1_reset_select_slave(sl)) {
> +		i = -ENXIO;
> +		goto error;
> +	}
> +
> +	/* Loop while there are still messages to transfer. */
> +	while (i < num) {
> +		/*
> +		 * Check for special case: Small write followed
> +		 * by read to same I2C device.
> +		 */
> +		if (i < (num-1)
> +			&& msgs[i].addr == msgs[i+1].addr
> +			&& !(msgs[i].flags & I2C_M_RD)
> +			&& (msgs[i+1].flags & I2C_M_RD)
> +			&& (msgs[i].len <= W1_F19_WRITE_DATA_LIMIT)) {
> +			/*
> +			 * The DS28E17 has a combined transfer
> +			 * for small write+read.
> +			 */
> +			result = w1_f19_i2c_write_read(sl, msgs[i].addr,
> +				msgs[i].buf, msgs[i].len,
> +				msgs[i+1].buf, msgs[i+1].len);
> +			if (result < 0) {
> +				i = result;
> +				goto error;
> +			}
> +
> +			/*
> +			 * Check if we should interpret the read data
> +			 * as a length byte. The DS28E17 unfortunately
> +			 * has no read without stop, so we can just do
> +			 * another simple read in that case.
> +			 */
> +			if (msgs[i+1].flags & I2C_M_RECV_LEN) {
> +				result = w1_f19_i2c_read(sl, msgs[i+1].addr,
> +					&(msgs[i+1].buf[1]), msgs[i+1].buf[0]);
> +				if (result < 0) {
> +					i = result;
> +					goto error;
> +				}
> +			}
> +
> +			/* Eat up read message, too. */
> +			i++;
> +		} else if (msgs[i].flags & I2C_M_RD) {
> +			/* Read transfer. */
> +			result = w1_f19_i2c_read(sl, msgs[i].addr,
> +				msgs[i].buf, msgs[i].len);
> +			if (result < 0) {
> +				i = result;
> +				goto error;
> +			}
> +
> +			/*
> +			 * Check if we should interpret the read data
> +			 * as a length byte. The DS28E17 unfortunately
> +			 * has no read without stop, so we can just do
> +			 * another simple read in that case.
> +			 */
> +			if (msgs[i].flags & I2C_M_RECV_LEN) {
> +				result = w1_f19_i2c_read(sl,
> +					msgs[i].addr,
> +					&(msgs[i].buf[1]),
> +					msgs[i].buf[0]);
> +				if (result < 0) {
> +					i = result;
> +					goto error;
> +				}
> +			}
> +		} else {
> +			/*
> +			 * Write transfer.
> +			 * Stop condition only for last
> +			 * transfer.
> +			 */
> +			result = w1_f19_i2c_write(sl,
> +				msgs[i].addr,
> +				msgs[i].buf,
> +				msgs[i].len,
> +				i == (num-1));
> +			if (result < 0) {
> +				i = result;
> +				goto error;
> +			}
> +		}
> +
> +		/* Next message. */
> +		i++;
> +
> +		/* Are there still messages to send/receive? */
> +		if (i < num) {
> +			/* Yes. Resume to same DS28E17. */
> +			if (w1_reset_resume_command(sl->master)) {
> +				i = -ENXIO;
> +				goto error;
> +			}
> +		}
> +	}
> +
> +error:
> +	/* End onewire transaction. */
> +	mutex_unlock(&sl->master->bus_mutex);
> +
> +	/* Return number of messages processed or error. */
> +	return i;
> +}
> +
> +
> +/* Get I2C adapter functionality. */
> +static u32 w1_f19_i2c_functionality(struct i2c_adapter *adapter)
> +{
> +	/*
> +	 * Plain I2C functions only.
> +	 * SMBus is emulated by the kernel's I2C layer.
> +	 * No "I2C_FUNC_SMBUS_QUICK"
> +	 * No "I2C_FUNC_SMBUS_READ_BLOCK_DATA"
> +	 * No "I2C_FUNC_SMBUS_BLOCK_PROC_CALL"
> +	 */
> +	return I2C_FUNC_I2C |
> +		I2C_FUNC_SMBUS_BYTE |
> +		I2C_FUNC_SMBUS_BYTE_DATA |
> +		I2C_FUNC_SMBUS_WORD_DATA |
> +		I2C_FUNC_SMBUS_PROC_CALL |
> +		I2C_FUNC_SMBUS_WRITE_BLOCK_DATA |
> +		I2C_FUNC_SMBUS_I2C_BLOCK |
> +		I2C_FUNC_SMBUS_PEC;
> +}
> +
> +
> +/* I2C algorithm. */
> +static const struct i2c_algorithm w1_f19_i2c_algorithm = {
> +	.master_xfer    = w1_f19_i2c_master_transfer,
> +	.smbus_xfer     = NULL,

Not needed.

> +	.functionality  = w1_f19_i2c_functionality,

You could add the quirks struct here since it is static.

> +};
> +
> +
> +/* I2C adapter quirks. */
> +static const struct i2c_adapter_quirks w1_f19_i2c_adapter_quirks = {
> +	.max_read_len = W1_F19_READ_DATA_LIMIT,
> +};
> +
> +
> +/* Read I2C speed from DS28E17. */
> +static int w1_f19_get_i2c_speed(struct w1_slave *sl)
> +{
> +	struct w1_f19_data *data = sl->family_data;
> +	int result = -ENXIO;
> +
> +	/* Start onewire transaction. */
> +	mutex_lock(&sl->master->bus_mutex);
> +
> +	/* Select slave. */
> +	if (w1_reset_select_slave(sl))
> +		goto error;
> +
> +	/* Read slave configuration byte. */
> +	w1_write_8(sl->master, W1_F19_READ_CONFIGURATION);
> +	result = w1_read_8(sl->master);
> +	if (result < 0 || result > 2) {
> +		result = -EIO;
> +		goto error;
> +	}
> +
> +	/* Update speed in slave specific data. */
> +	data->speed = result;
> +
> +error:
> +	/* End onewire transaction. */
> +	mutex_unlock(&sl->master->bus_mutex);
> +
> +	return result;
> +}
> +
> +
> +/* Set I2C speed on DS28E17. */
> +static int __w1_f19_set_i2c_speed(struct w1_slave *sl, u8 speed)
> +{
> +	struct w1_f19_data *data = sl->family_data;
> +	const int i2c_speeds[3] = { 100, 400, 900 };
> +	u8 w1_buf[2];
> +
> +	/* Select slave. */
> +	if (w1_reset_select_slave(sl))
> +		return -ENXIO;
> +
> +	w1_buf[0] = W1_F19_WRITE_CONFIGURATION;
> +	w1_buf[1] = speed;
> +	w1_write_block(sl->master, w1_buf, 2);
> +
> +	/* Update speed in slave specific data. */
> +	data->speed = speed;
> +
> +	dev_info(&sl->dev, "i2c speed set to %d kBaud\n", i2c_speeds[speed]);
> +
> +	return 0;
> +}
> +
> +static int w1_f19_set_i2c_speed(struct w1_slave *sl, u8 speed)
> +{
> +	int result;
> +
> +	/* Start onewire transaction. */
> +	mutex_lock(&sl->master->bus_mutex);
> +
> +	/* Set I2C speed on DS28E17. */
> +	result = __w1_f19_set_i2c_speed(sl, speed);
> +
> +	/* End onewire transaction. */
> +	mutex_unlock(&sl->master->bus_mutex);
> +
> +	return result;
> +}
> +
> +
> +/* Sysfs attributes. */
> +
> +/* I2C speed attribute for a single chip. */
> +static ssize_t speed_show(struct device *dev, struct device_attribute *attr,
> +			     char *buf)
> +{
> +	struct w1_slave *sl = dev_to_w1_slave(dev);
> +	int result;
> +
> +	/* Read current speed from slave. Updates data->speed. */
> +	result = w1_f19_get_i2c_speed(sl);
> +	if (result < 0)
> +		return result;
> +
> +	/* Return current speed value. */
> +	return sprintf(buf, "%d\n", result);
> +}
> +
> +static ssize_t speed_store(struct device *dev, struct device_attribute *attr,
> +			      const char *buf, size_t count)
> +{
> +	struct w1_slave *sl = dev_to_w1_slave(dev);
> +	int error;
> +
> +	/* Valid values are: '0' (100kHz), '1' (400kHz), '2' (900kHz) */
> +	if (count < 1 || count > 2 || !buf)
> +		return -EINVAL;
> +	if (count == 2 && buf[1] != '\n')
> +		return -EINVAL;
> +	if (buf[0] != '0' && buf[0] != '1' && buf[0] != '2')
> +		return -EINVAL;
> +
> +	/* Set speed on slave. */
> +	error = w1_f19_set_i2c_speed(sl, buf[0] & 0x03);
> +	if (error < 0)
> +		return error;
> +
> +	/* Return bytes written. */
> +	return count;
> +}
> +
> +static DEVICE_ATTR_RW(speed);
> +
> +
> +/* Busy stretch attribute for a single chip. */
> +static ssize_t stretch_show(struct device *dev, struct device_attribute *attr,
> +			     char *buf)
> +{
> +	struct w1_slave *sl = dev_to_w1_slave(dev);
> +	struct w1_f19_data *data = sl->family_data;
> +
> +	/* Return current stretch value. */
> +	return sprintf(buf, "%d\n", data->stretch);
> +}
> +
> +static ssize_t stretch_store(struct device *dev, struct device_attribute *attr,
> +			      const char *buf, size_t count)
> +{
> +	struct w1_slave *sl = dev_to_w1_slave(dev);
> +	struct w1_f19_data *data = sl->family_data;
> +
> +	/* Valid values are '1' to '9' */
> +	if (count < 1 || count > 2 || !buf)
> +		return -EINVAL;
> +	if (count == 2 && buf[1] != '\n')
> +		return -EINVAL;
> +	if (buf[0] < '1' || buf[0] > '9')
> +		return -EINVAL;
> +
> +	/* Set busy stretch value. */
> +	data->stretch = buf[0] & 0x0F;
> +
> +	/* Return bytes written. */
> +	return count;
> +}
> +
> +static DEVICE_ATTR_RW(stretch);
> +
> +
> +/* All attributes. */
> +static struct attribute *w1_f19_attrs[] = {
> +	&dev_attr_speed.attr,
> +	&dev_attr_stretch.attr,
> +	NULL,
> +};
> +
> +static const struct attribute_group w1_f19_group = {
> +	.attrs		= w1_f19_attrs,
> +};
> +
> +static const struct attribute_group *w1_f19_groups[] = {
> +	&w1_f19_group,
> +	NULL,
> +};

sysfs files need documentation in Documentation/ABI/testing/.

> +
> +
> +/* Slave add and remove functions. */
> +static int w1_f19_add_slave(struct w1_slave *sl)
> +{
> +	struct w1_f19_data *data = NULL;
> +
> +	/* Allocate memory for slave specific data. */
> +	data = kzalloc(sizeof(*data), GFP_KERNEL);

I don't know w1 much. Isn't there a device so we could use devm_kzalloc?

> +	if (!data)
> +		return -ENOMEM;
> +	sl->family_data = data;
> +
> +	/* Setup default I2C speed on slave. */
> +	if (i2c_speed == 0 || i2c_speed == 1 || i2c_speed == 2) {
> +		__w1_f19_set_i2c_speed(sl, i2c_speed);
> +	}	else {
> +		/*
> +		 * A module parameter of anything else than 0, 1, 2
> +		 * means not to touch the speed of the DS28E17.
> +		 * We assume 400kBaud.
> +		 */

I suggest to to use 100kHz as the default. That's what all devices have
to support. 400kHz is common, but still optional.

> +		data->speed = 1;
> +	}
> +
> +	/*
> +	 * Setup default busy stretch
> +	 * configuration for the DS28E17.
> +	 */
> +	data->stretch = i2c_stretch;
> +
> +	/* Setup I2C adapter. */
> +	data->adapter.owner      = THIS_MODULE;
> +	data->adapter.class      = 0;

Not needed with kzalloc.

> +	data->adapter.algo       = &w1_f19_i2c_algorithm;
> +	data->adapter.alogo_data  = (void *) sl;

No need to cast to void*.

> +	strcpy(data->adapter.name, "w1-");
> +	strcat(data->adapter.name, sl->name);
> +	data->adapter.dev.parent = &sl->dev;
> +	data->adapter.quirks     = &w1_f19_i2c_adapter_quirks;
> +
> +	return i2c_add_adapter(&data->adapter);
> +}
> +
> +static void w1_f19_remove_slave(struct w1_slave *sl)
> +{
> +	/* Delete I2C adapter. */
> +	i2c_del_adapter(&(((struct w1_f19_data *)(sl->family_data))->adapter));

Would be more readable if you'd use a 'family_data' variable as an
intermediate step.

> +
> +	/* Free slave specific data. */
> +	kfree(sl->family_data);
> +	sl->family_data = NULL;
> +}
> +
> +
> +/* Declarations within the w1 subsystem. */
> +static struct w1_family_ops w1_f19_fops = {
> +	.add_slave = w1_f19_add_slave,
> +	.remove_slave = w1_f19_remove_slave,
> +	.groups = w1_f19_groups,
> +};
> +
> +static struct w1_family w1_family_19 = {
> +	.fid = W1_FAMILY_DS28E17,
> +	.fops = &w1_f19_fops,
> +};
> +
> +
> +/* Module init and remove functions. */
> +static int __init w1_f19_init(void)
> +{
> +	return w1_register_family(&w1_family_19);
> +}
> +
> +static void __exit w1_f19_fini(void)
> +{
> +	w1_unregister_family(&w1_family_19);
> +}
> +
> +module_init(w1_f19_init);
> +module_exit(w1_f19_fini);

use the 'module_driver' macro?

> +
> diff --git a/drivers/w1/w1_family.h b/drivers/w1/w1_family.h
> index ed5dcb8..5016a76 100644
> --- a/drivers/w1/w1_family.h
> +++ b/drivers/w1/w1_family.h
> @@ -31,6 +31,7 @@
>  #define W1_FAMILY_SMEM_01	0x01
>  #define W1_FAMILY_SMEM_81	0x81
>  #define W1_THERM_DS18S20 	0x10
> +#define W1_FAMILY_DS28E17	0x19
>  #define W1_FAMILY_DS28E04	0x1C
>  #define W1_COUNTER_DS2423	0x1D
>  #define W1_THERM_DS1822  	0x22
> -- 
> 2.1.4
>
Jan Kandziora July 22, 2016, 8:52 p.m. | #5
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Am 21.07.2016 um 09:02 schrieb Wolfram Sang:
>> + +	  In addition, that new I2C bus is accessible from userspace
>> through +	  a /dev/i2c-nnn device node if you have enabled +
>> "Device Drivers->I2C Support->I2C device interface"
>> (CONFIG_I2C_CHARDEV).
> 
> I think the last paragraph can go. This is standard I2C behaviour
> and Kconfig is not the right place to document this.
> 
I changed the first paragraph, too "to be used by the kernel and
userspace tools".


>> + +#include <linux/kernel.h> +#include <linux/module.h> +#include
>> <linux/moduleparam.h> +#include <linux/device.h> +#include
>> <linux/types.h> +#include <linux/delay.h> +#include
>> <linux/slab.h> +#include <linux/crc16.h> +#include
>> <linux/uaccess.h> +#include <linux/i2c.h>
> 
> If you sort these, it is easier to avoid duplicates later.
> 
Done.


>> + +#define CRC16_INIT 0 + +#include "../w1.h" +#include
>> "../w1_int.h" +#include "../w1_family.h" + + +/* Module setup.
>> */ +MODULE_LICENSE("GPL");
> 
> "GPL v2"
> 
Done.


>> +MODULE_AUTHOR("Jan Kandziora <jjj@gmx.de>"); 
>> +MODULE_DESCRIPTION("w1 family 19 driver for DS28E17, 1-wire to
>> I2C master bridge"); +MODULE_ALIAS("w1-family-"
>> __stringify(W1_FAMILY_DS28E17)); + + +/* Default I2C speed to be
>> set when a DS28E17 is detected. */ +static char i2c_speed = 1; 
>> +module_param_named(speed, i2c_speed, byte, (S_IRUSR |
>> S_IWUSR)); +MODULE_PARM_DESC(speed, "Default I2C speed to be set
>> when a DS28E17 is detected");
> 
> I don't see any documentation what 0,1,2 means. I think it would be
> more user friendly to actually use the kHz values here.
> 
Okay.


> 
>> +/* Default I2C stretch value to be set when a DS28E17 is
>> detected. */ +static char i2c_stretch = 1; 
>> +module_param_named(stretch, i2c_stretch, byte, (S_IRUSR |
>> S_IWUSR)); +MODULE_PARM_DESC(stretch, "Default I2C stretch value
>> to be set when a DS28E17 is detected");
> 
> No documentation what the value means.
> 
In which file(s) should I document it?


>> +	if (w1_buf[0] & W1_F19_STATUS_ADDRESS) +		dev_warn(&sl->dev,
>> "i2c device not responding\n");
> 
> This should ideally return -ENXIO.
> 
Done.


>> +	if (w1_buf[0] & W1_F19_STATUS_START) +		dev_warn(&sl->dev, "i2c
>> start condition invalid\n");
> 
> Does that mean "arbitration lost"? Then it should return
> "-EAGAIN".
> 
The DS28E17 datasheet says nothing about it but 0="start" and
1="invalid start", page 23.

I think you are right, this has to be arbitration lost. EAGAIN and no
warning message then.


>> + +	/* Check input. */ +	if (i2c_address > 0x7F
> 
> The i2c core checks that for you.
> 
Done.


>> +			|| count == 0)
> 
> For that case, better return -EOPNOTSUPP;
> 
Done.



>> + +		/* Resume to same DS28E17. */ +		if
>> (w1_reset_resume_command(sl->master)) +			return -ENXIO;
> 
> -ENXIO? Please check Documentation/i2c/fault-codes if that fits
> 



>> + +	/* Check input. */ +	if (i2c_address > 0x7F +			|| count >
>> W1_F19_READ_DATA_LIMIT
> 
> Since you have a quirk structure, the core checks this for you,
> too.
> 
Okay, removed.


>> +			|| count == 0) +		return -EINVAL;
> 
> -EOPNOTSUPP.
> 
Done.


>> +	/* Warnings. */ +	if (w1_buf[0] & W1_F19_STATUS_CRC) +
>> dev_warn(&sl->dev, "crc16 mismatch\n"); +	if (w1_buf[0] &
>> W1_F19_STATUS_ADDRESS) +		dev_warn(&sl->dev, "i2c device not
>> responding\n"); +	if (w1_buf[0] & W1_F19_STATUS_START) +
>> dev_warn(&sl->dev, "i2c start condition invalid\n");
> 
> Same as above.
> 
Done.


>> + +	/* Check input. */ +	if (i2c_address > 0x7F +			|| wcount ==
>> 0 +			|| rcount > W1_F19_READ_DATA_LIMIT +			|| rcount == 0) +
>> return -EINVAL;
> 
> Same comments as above
> 
Done.


>> + +	/* Warnings. */ +	if (w1_buf[0] & W1_F19_STATUS_CRC) +
>> dev_warn(&sl->dev, "crc16 mismatch\n"); +	if (w1_buf[0] &
>> W1_F19_STATUS_ADDRESS) +		dev_warn(&sl->dev, "i2c device not
>> responding\n"); +	if (w1_buf[0] & W1_F19_STATUS_START) +
>> dev_warn(&sl->dev, "i2c start condition invalid\n"); +	if
>> ((w1_buf[0] & (W1_F19_STATUS_CRC | W1_F19_STATUS_ADDRESS)) == 0 +
>> && w1_buf[1] != 0) { +		dev_warn(&sl->dev, "i2c short write, %d
>> bytes not acknowledged\n", +			w1_buf[1]); +	} + +	/* Check error
>> conditions. */ +	if (w1_buf[0] != 0 || w1_buf[1] != 0) +		return
>> -EIO;
> 
> ditto. Maybe you should put this parsing into a seperate function?
> 
Done: w1_f19_error().


>> + +	/* Read received I2C data from DS28E17. */ +	return
>> w1_read_block(sl->master, rbuffer, rcount); +} + + +/* Do an I2C
>> master transfer. */ +static int w1_f19_i2c_master_transfer(struct
>> i2c_adapter *adapter, +	struct i2c_msg *msgs, int num) +{ +
>> struct w1_slave *sl = (struct w1_slave *) adapter->algo_data; +
>> int i = 0; +	int result = 0; + +	/* Return if no messages to
>> send/receive. */ +	if (num == 0) +		return 0;
> 
> Heh, I was about to write "the core will check this for you", but
> it doesn't. I'll send a patch to fix that, thanks! So please remove
> it here.
> 
You're welcome. And done.



>> + +/* I2C algorithm. */ +static const struct i2c_algorithm
>> w1_f19_i2c_algorithm = { +	.master_xfer    =
>> w1_f19_i2c_master_transfer, +	.smbus_xfer     = NULL,
> 
> Not needed.
> 
Done.


>> +	.functionality  = w1_f19_i2c_functionality,
> 
> You could add the quirks struct here since it is static.
> 
Done.


>> + +/* All attributes. */ +static struct attribute *w1_f19_attrs[]
>> = { +	&dev_attr_speed.attr, +	&dev_attr_stretch.attr, +	NULL, 
>> +}; + +static const struct attribute_group w1_f19_group = { +
>> .attrs		= w1_f19_attrs, +}; + +static const struct
>> attribute_group *w1_f19_groups[] = { +	&w1_f19_group, +	NULL, 
>> +};
> 
> sysfs files need documentation in Documentation/ABI/testing/.
> 
Ah, okay. Will add that.


>> + + +/* Slave add and remove functions. */ +static int
>> w1_f19_add_slave(struct w1_slave *sl) +{ +	struct w1_f19_data
>> *data = NULL; + +	/* Allocate memory for slave specific data. */ 
>> +	data = kzalloc(sizeof(*data), GFP_KERNEL);
> 
> I don't know w1 much. Isn't there a device so we could use
> devm_kzalloc?
> 
Evgeniy?


>> +	if (!data) +		return -ENOMEM; +	sl->family_data = data; + +	/*
>> Setup default I2C speed on slave. */ +	if (i2c_speed == 0 ||
>> i2c_speed == 1 || i2c_speed == 2) { +		__w1_f19_set_i2c_speed(sl,
>> i2c_speed); +	}	else { +		/* +		 * A module parameter of anything
>> else than 0, 1, 2 +		 * means not to touch the speed of the
>> DS28E17. +		 * We assume 400kBaud. +		 */
> 
> I suggest to to use 100kHz as the default. That's what all devices
> have to support. 400kHz is common, but still optional.
> 
Okay.


>> +		data->speed = 1; +	} + +	/* +	 * Setup default busy stretch +
>> * configuration for the DS28E17. +	 */ +	data->stretch =
>> i2c_stretch; + +	/* Setup I2C adapter. */ +	data->adapter.owner
>> = THIS_MODULE; +	data->adapter.class      = 0;
> 
> Not needed with kzalloc.
> 
Okay.


>> +	data->adapter.algo       = &w1_f19_i2c_algorithm; +
>> data->adapter.alogo_data  = (void *) sl;
> 
> No need to cast to void*.
> 
Ah.


>> +	strcpy(data->adapter.name, "w1-"); +	strcat(data->adapter.name,
>> sl->name); +	data->adapter.dev.parent = &sl->dev; +
>> data->adapter.quirks     = &w1_f19_i2c_adapter_quirks; + +	return
>> i2c_add_adapter(&data->adapter); +} + +static void
>> w1_f19_remove_slave(struct w1_slave *sl) +{ +	/* Delete I2C
>> adapter. */ +	i2c_del_adapter(&(((struct w1_f19_data
>> *)(sl->family_data))->adapter));
> 
> Would be more readable if you'd use a 'family_data' variable as an 
> intermediate step.
> 
Done.


>> + +	/* Free slave specific data. */ +	kfree(sl->family_data); +
>> sl->family_data = NULL; +} + + +/* Declarations within the w1
>> subsystem. */ +static struct w1_family_ops w1_f19_fops = { +
>> .add_slave = w1_f19_add_slave, +	.remove_slave =
>> w1_f19_remove_slave, +	.groups = w1_f19_groups, +}; + +static
>> struct w1_family w1_family_19 = { +	.fid = W1_FAMILY_DS28E17, +
>> .fops = &w1_f19_fops, +}; + + +/* Module init and remove
>> functions. */ +static int __init w1_f19_init(void) +{ +	return
>> w1_register_family(&w1_family_19); +} + +static void __exit
>> w1_f19_fini(void) +{ +	w1_unregister_family(&w1_family_19); +} + 
>> +module_init(w1_f19_init); +module_exit(w1_f19_fini);
> 
> use the 'module_driver' macro?
> 
To be honest, the examples of the __driver argument I found in the few
other drivers which use that macro made me shy away.

It's like doing the taxes. Forms and more forms to fill out...

I would use it if someone tells me what to fill in there.

Kind regards

	Jan
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Jan Kandziora July 22, 2016, 8:56 p.m. | #6
Am 21.07.2016 um 09:02 schrieb Wolfram Sang:
>> + +		/* Resume to same DS28E17. */ +		if 
>> (w1_reset_resume_command(sl->master)) +			return -ENXIO;
> 
> -ENXIO? Please check Documentation/i2c/fault-codes if that fits
> 
It's an error while addressing the DS28E17. I'm not sure about this,
what to return when the bus master has gone, which may be only a
temporary problem.


Kind regards

	Jan
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Evgeniy Polyakov July 23, 2016, 4:44 a.m. | #7
20.07.2016, 21:19, "Jan Kandziora" <jjj@gmx.de>:
> Am 20.07.2016 um 19:34 schrieb Evgeniy Polyakov:
>>  Is that a hardware limitation that there is no interrupt or other
>>  completion mechanism which would handle this case?
>
> Ah, forgot to address that question.
>
> The DS28E17 has a BUSY pin. We could add an interrupt-driven busy
> mechanism but the mechanism without the interrupt line has to stay in
> there because most people wouldn't add an interrupt line to their
> Onewire installation just for having that.

Ok, I see, its just a hardware issue which requires to have this potentially unhealthy busy loop.

Both patches look good to me, thank you.
Acked-by: Evgeniy Polyakov <zbr@ioremap.net>
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Patch

diff --git a/drivers/w1/slaves/Kconfig b/drivers/w1/slaves/Kconfig
index cfe74d0..9a9a422 100644
--- a/drivers/w1/slaves/Kconfig
+++ b/drivers/w1/slaves/Kconfig
@@ -126,6 +126,25 @@  config W1_SLAVE_DS28E04
 
 	  If you are unsure, say N.
 
+config W1_SLAVE_DS28E17
+	tristate "1-wire-to-I2C master bridge (DS28E17)"
+	select CRC16
+	depends on I2C
+	help
+	  Say Y here if you want to use the DS28E17 1-wire-to-I2C master bridge.
+	  For each DS28E17 detected, a new I2C adapter is created within the
+	  kernel. I2C devices on that bus can be configured to be used by the
+	  kernel as on any other "native" I2C bus.
+
+	  In addition, that new I2C bus is accessible from userspace through
+	  a /dev/i2c-nnn device node if you have enabled
+	  "Device Drivers->I2C Support->I2C device interface" (CONFIG_I2C_CHARDEV).
+
+	  This driver is also available as a module. If so, the module
+	  will be called w1_ds28e17.
+
+	  If you are unsure, say N.
+
 config W1_SLAVE_BQ27000
 	tristate "BQ27000 slave support"
 	help
diff --git a/drivers/w1/slaves/Makefile b/drivers/w1/slaves/Makefile
index 1e9989a..3fa1625 100644
--- a/drivers/w1/slaves/Makefile
+++ b/drivers/w1/slaves/Makefile
@@ -15,3 +15,4 @@  obj-$(CONFIG_W1_SLAVE_DS2780)	+= w1_ds2780.o
 obj-$(CONFIG_W1_SLAVE_DS2781)	+= w1_ds2781.o
 obj-$(CONFIG_W1_SLAVE_BQ27000)	+= w1_bq27000.o
 obj-$(CONFIG_W1_SLAVE_DS28E04)	+= w1_ds28e04.o
+obj-$(CONFIG_W1_SLAVE_DS28E17)	+= w1_ds28e17.o
diff --git a/drivers/w1/slaves/w1_ds28e17.c b/drivers/w1/slaves/w1_ds28e17.c
new file mode 100644
index 0000000..b66c879
--- /dev/null
+++ b/drivers/w1/slaves/w1_ds28e17.c
@@ -0,0 +1,761 @@ 
+/*
+ *	w1_ds28e17.c - w1 family 19 (DS28E17) driver
+ *
+ * Copyright (c) 2016 Jan Kandziora <jjj@gmx.de>
+ *
+ * This source code is licensed under the GNU General Public License,
+ * Version 2. See the file COPYING for more details.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/device.h>
+#include <linux/types.h>
+#include <linux/delay.h>
+#include <linux/slab.h>
+#include <linux/crc16.h>
+#include <linux/uaccess.h>
+#include <linux/i2c.h>
+
+#define CRC16_INIT 0
+
+#include "../w1.h"
+#include "../w1_int.h"
+#include "../w1_family.h"
+
+
+/* Module setup. */
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Jan Kandziora <jjj@gmx.de>");
+MODULE_DESCRIPTION("w1 family 19 driver for DS28E17, 1-wire to I2C master bridge");
+MODULE_ALIAS("w1-family-" __stringify(W1_FAMILY_DS28E17));
+
+
+/* Default I2C speed to be set when a DS28E17 is detected. */
+static char i2c_speed = 1;
+module_param_named(speed, i2c_speed, byte, (S_IRUSR | S_IWUSR));
+MODULE_PARM_DESC(speed, "Default I2C speed to be set when a DS28E17 is detected");
+
+/* Default I2C stretch value to be set when a DS28E17 is detected. */
+static char i2c_stretch = 1;
+module_param_named(stretch, i2c_stretch, byte, (S_IRUSR | S_IWUSR));
+MODULE_PARM_DESC(stretch, "Default I2C stretch value to be set when a DS28E17 is detected");
+
+/* DS28E17 device command codes. */
+#define W1_F19_WRITE_DATA_WITH_STOP      0x4B
+#define W1_F19_WRITE_DATA_NO_STOP        0x5A
+#define W1_F19_WRITE_DATA_ONLY           0x69
+#define W1_F19_WRITE_DATA_ONLY_WITH_STOP 0x78
+#define W1_F19_READ_DATA_WITH_STOP       0x87
+#define W1_F19_WRITE_READ_DATA_WITH_STOP 0x2D
+#define W1_F19_WRITE_CONFIGURATION       0xD2
+#define W1_F19_READ_CONFIGURATION        0xE1
+#define W1_F19_ENABLE_SLEEP_MODE         0x1E
+#define W1_F19_READ_DEVICE_REVISION      0xC4
+
+/* DS28E17 status bits */
+#define W1_F19_STATUS_CRC     0x01
+#define W1_F19_STATUS_ADDRESS 0x02
+#define W1_F19_STATUS_START   0x08
+
+/*
+ * Maximum number of I2C bytes to transfer within one CRC16 protected onewire
+ * command.
+ * */
+#define W1_F19_WRITE_DATA_LIMIT 255
+
+/* Maximum number of I2C bytes to read with one onewire command. */
+#define W1_F19_READ_DATA_LIMIT 255
+
+/* Contants for calculating the busy sleep. */
+#define W1_F19_BUSY_TIMEBASES { 90, 23, 10 }
+#define W1_F19_BUSY_GRATUITY  1000
+
+/* Number of checks for the busy flag before timeout. */
+#define W1_F19_BUSY_CHECKS 1000
+
+
+/* Slave specific data. */
+struct w1_f19_data {
+	u8 speed;
+	u8 stretch;
+	struct i2c_adapter adapter;
+};
+
+
+/* Wait a while until the busy flag clears. */
+static int w1_f19_i2c_busy_wait(struct w1_slave *sl, size_t count)
+{
+	const unsigned long timebases[3] = W1_F19_BUSY_TIMEBASES;
+	struct w1_f19_data *data = sl->family_data;
+	unsigned int checks;
+
+	/* Check the busy flag first in any case.*/
+	if (w1_touch_bit(sl->master, 1) == 0)
+		return 0;
+
+	/*
+	 * Do a generously long sleep in the beginning,
+	 * as we have to wait at least this time for all
+	 * the I2C bytes at the given speed to be transferred.
+	 */
+	usleep_range(timebases[data->speed] * (data->stretch) * count,
+		timebases[data->speed] * (data->stretch) * count
+		+ W1_F19_BUSY_GRATUITY);
+
+	/* Now continusly check the busy flag sent by the DS28E17. */
+	checks = W1_F19_BUSY_CHECKS;
+	while ((checks--) > 0) {
+		/* Return success if the busy flag is cleared. */
+		if (w1_touch_bit(sl->master, 1) == 0)
+			return 0;
+
+		/* Wait one non-streched byte timeslot. */
+		udelay(timebases[data->speed]);
+	}
+
+	/* Timeout. */
+	dev_warn(&sl->dev, "busy timeout\n");
+	return -EIO;
+}
+
+
+/* Utility function: write data to I2C slave, single chunk. */
+static int __w1_f19_i2c_write(struct w1_slave *sl,
+	const u8 *command, size_t command_count,
+	const u8 *buffer, size_t count)
+{
+	u16 crc;
+	u8 w1_buf[2];
+
+	/* Send command and I2C data to DS28E17. */
+	crc = crc16(CRC16_INIT, command, command_count);
+	w1_write_block(sl->master, command, command_count);
+
+	w1_buf[0] = count;
+	crc = crc16(crc, w1_buf, 1);
+	w1_write_8(sl->master, w1_buf[0]);
+
+	crc = crc16(crc, buffer, count);
+	w1_write_block(sl->master, buffer, count);
+
+	w1_buf[0] = ~(crc & 0xFF);
+	w1_buf[1] = ~((crc >> 8) & 0xFF);
+	w1_write_block(sl->master, w1_buf, 2);
+
+	/* Wait until busy flag clears (or timeout). */
+	if (w1_f19_i2c_busy_wait(sl, count + 1) < 0)
+		return -EIO;
+
+	/* Read status from DS28E17. */
+	w1_read_block(sl->master, w1_buf, 2);
+
+	/* Warnings. */
+	if (w1_buf[0] & W1_F19_STATUS_CRC)
+		dev_warn(&sl->dev, "crc16 mismatch\n");
+	if (w1_buf[0] & W1_F19_STATUS_ADDRESS)
+		dev_warn(&sl->dev, "i2c device not responding\n");
+	if (w1_buf[0] & W1_F19_STATUS_START)
+		dev_warn(&sl->dev, "i2c start condition invalid\n");
+	if ((w1_buf[0] & (W1_F19_STATUS_CRC | W1_F19_STATUS_ADDRESS)) == 0
+			&& w1_buf[1] != 0) {
+		dev_warn(&sl->dev, "i2c short write, %d bytes not acknowledged\n",
+			w1_buf[1]);
+	}
+
+	/* Check error conditions. */
+	if (w1_buf[0] != 0 || w1_buf[1] != 0)
+		return -EIO;
+
+	/* All ok. */
+	return count;
+}
+
+
+/* Write data to I2C slave. */
+static int w1_f19_i2c_write(struct w1_slave *sl, u16 i2c_address,
+	const u8 *buffer, size_t count, bool stop)
+{
+	int result;
+	int remaining = count;
+	const u8 *p;
+	u8 command[2];
+
+	/* Check input. */
+	if (i2c_address > 0x7F
+			|| count == 0)
+		return 0;
+
+	/* Check whether we need multiple commands. */
+	if (count <= W1_F19_WRITE_DATA_LIMIT) {
+		/*
+		 * Small data amount. Data can be sent with
+		 * a single onewire command.
+		 */
+
+		/* Send all data to DS28E17. */
+		command[0] = (stop ? W1_F19_WRITE_DATA_WITH_STOP
+			: W1_F19_WRITE_DATA_NO_STOP);
+		command[1] = i2c_address << 1;
+		result = __w1_f19_i2c_write(sl, command, 2, buffer, count);
+	} else {
+		/* Large data amount. Data has to be sent in multiple chunks. */
+
+		/* Send first chunk to DS28E17. */
+		p = buffer;
+		command[0] = W1_F19_WRITE_DATA_NO_STOP;
+		command[1] = i2c_address << 1;
+		result = __w1_f19_i2c_write(sl, command, 2, p,
+			W1_F19_WRITE_DATA_LIMIT);
+		if (result < 0)
+			return result;
+
+		/* Resume to same DS28E17. */
+		if (w1_reset_resume_command(sl->master))
+			return -ENXIO;
+
+		/* Next data chunk. */
+		p += W1_F19_WRITE_DATA_LIMIT;
+		remaining -= W1_F19_WRITE_DATA_LIMIT;
+
+		while (remaining > W1_F19_WRITE_DATA_LIMIT) {
+			/* Send intermediate chunk to DS28E17. */
+			command[0] = W1_F19_WRITE_DATA_ONLY;
+			result = __w1_f19_i2c_write(sl, command, 1, p,
+					W1_F19_WRITE_DATA_LIMIT);
+			if (result < 0)
+				return result;
+
+			/* Resume to same DS28E17. */
+			if (w1_reset_resume_command(sl->master))
+				return -ENXIO;
+
+			/* Next data chunk. */
+			p += W1_F19_WRITE_DATA_LIMIT;
+			remaining -= W1_F19_WRITE_DATA_LIMIT;
+		}
+
+		/* Send final chunk to DS28E17. */
+		command[0] = (stop ? W1_F19_WRITE_DATA_ONLY_WITH_STOP
+			: W1_F19_WRITE_DATA_ONLY);
+		result = __w1_f19_i2c_write(sl, command, 1, p, remaining);
+	}
+
+	return result;
+}
+
+
+/* Read data from I2C slave. */
+static int w1_f19_i2c_read(struct w1_slave *sl, u16 i2c_address,
+	u8 *buffer, size_t count)
+{
+	u16 crc;
+	u8 w1_buf[5];
+
+	/* Check input. */
+	if (i2c_address > 0x7F
+			|| count > W1_F19_READ_DATA_LIMIT
+			|| count == 0)
+		return -EINVAL;
+
+	/* Send command to DS28E17. */
+	w1_buf[0] = W1_F19_READ_DATA_WITH_STOP;
+	w1_buf[1] = i2c_address << 1 | 0x01;
+	w1_buf[2] = count;
+	crc = crc16(CRC16_INIT, w1_buf, 3);
+	w1_buf[3] = ~(crc & 0xFF);
+	w1_buf[4] = ~((crc >> 8) & 0xFF);
+	w1_write_block(sl->master, w1_buf, 5);
+
+	/* Wait until busy flag clears (or timeout). */
+	if (w1_f19_i2c_busy_wait(sl, count + 1) < 0)
+		return -EIO;
+
+	/* Read status from DS28E17. */
+	w1_buf[0] = w1_read_8(sl->master);
+
+	/* Warnings. */
+	if (w1_buf[0] & W1_F19_STATUS_CRC)
+		dev_warn(&sl->dev, "crc16 mismatch\n");
+	if (w1_buf[0] & W1_F19_STATUS_ADDRESS)
+		dev_warn(&sl->dev, "i2c device not responding\n");
+	if (w1_buf[0] & W1_F19_STATUS_START)
+		dev_warn(&sl->dev, "i2c start condition invalid\n");
+
+	/* Check error conditions. */
+	if (w1_buf[0] != 0)
+		return -EIO;
+
+	/* Read received I2C data from DS28E17. */
+	return w1_read_block(sl->master, buffer, count);
+}
+
+
+/* Write to, then read data from I2C slave. */
+static int w1_f19_i2c_write_read(struct w1_slave *sl, u16 i2c_address,
+	const u8 *wbuffer, size_t wcount, u8 *rbuffer, size_t rcount)
+{
+	u16 crc;
+	u8 w1_buf[3];
+
+	/* Check input. */
+	if (i2c_address > 0x7F
+			|| wcount == 0
+			|| rcount > W1_F19_READ_DATA_LIMIT
+			|| rcount == 0)
+		return -EINVAL;
+
+	/* Send command and I2C data to DS28E17. */
+	w1_buf[0] = W1_F19_WRITE_READ_DATA_WITH_STOP;
+	w1_buf[1] = i2c_address << 1;
+	w1_buf[2] = wcount;
+	crc = crc16(CRC16_INIT, w1_buf, 3);
+	w1_write_block(sl->master, w1_buf, 3);
+
+	crc = crc16(crc, wbuffer, wcount);
+	w1_write_block(sl->master, wbuffer, wcount);
+
+	w1_buf[0] = rcount;
+	crc = crc16(crc, w1_buf, 1);
+	w1_buf[1] = ~(crc & 0xFF);
+	w1_buf[2] = ~((crc >> 8) & 0xFF);
+	w1_write_block(sl->master, w1_buf, 3);
+
+	/* Wait until busy flag clears (or timeout). */
+	if (w1_f19_i2c_busy_wait(sl, wcount + rcount + 2) < 0)
+		return -EIO;
+
+	/* Read status from DS28E17. */
+	w1_read_block(sl->master, w1_buf, 2);
+
+	/* Warnings. */
+	if (w1_buf[0] & W1_F19_STATUS_CRC)
+		dev_warn(&sl->dev, "crc16 mismatch\n");
+	if (w1_buf[0] & W1_F19_STATUS_ADDRESS)
+		dev_warn(&sl->dev, "i2c device not responding\n");
+	if (w1_buf[0] & W1_F19_STATUS_START)
+		dev_warn(&sl->dev, "i2c start condition invalid\n");
+	if ((w1_buf[0] & (W1_F19_STATUS_CRC | W1_F19_STATUS_ADDRESS)) == 0
+			&& w1_buf[1] != 0) {
+		dev_warn(&sl->dev, "i2c short write, %d bytes not acknowledged\n",
+			w1_buf[1]);
+	}
+
+	/* Check error conditions. */
+	if (w1_buf[0] != 0 || w1_buf[1] != 0)
+		return -EIO;
+
+	/* Read received I2C data from DS28E17. */
+	return w1_read_block(sl->master, rbuffer, rcount);
+}
+
+
+/* Do an I2C master transfer. */
+static int w1_f19_i2c_master_transfer(struct i2c_adapter *adapter,
+	struct i2c_msg *msgs, int num)
+{
+	struct w1_slave *sl = (struct w1_slave *) adapter->algo_data;
+	int i = 0;
+	int result = 0;
+
+	/* Return if no messages to send/receive. */
+	if (num == 0)
+		return 0;
+
+	/* Start onewire transaction. */
+	mutex_lock(&sl->master->bus_mutex);
+
+	/* Select DS28E17. */
+	if (w1_reset_select_slave(sl)) {
+		i = -ENXIO;
+		goto error;
+	}
+
+	/* Loop while there are still messages to transfer. */
+	while (i < num) {
+		/*
+		 * Check for special case: Small write followed
+		 * by read to same I2C device.
+		 */
+		if (i < (num-1)
+			&& msgs[i].addr == msgs[i+1].addr
+			&& !(msgs[i].flags & I2C_M_RD)
+			&& (msgs[i+1].flags & I2C_M_RD)
+			&& (msgs[i].len <= W1_F19_WRITE_DATA_LIMIT)) {
+			/*
+			 * The DS28E17 has a combined transfer
+			 * for small write+read.
+			 */
+			result = w1_f19_i2c_write_read(sl, msgs[i].addr,
+				msgs[i].buf, msgs[i].len,
+				msgs[i+1].buf, msgs[i+1].len);
+			if (result < 0) {
+				i = result;
+				goto error;
+			}
+
+			/*
+			 * Check if we should interpret the read data
+			 * as a length byte. The DS28E17 unfortunately
+			 * has no read without stop, so we can just do
+			 * another simple read in that case.
+			 */
+			if (msgs[i+1].flags & I2C_M_RECV_LEN) {
+				result = w1_f19_i2c_read(sl, msgs[i+1].addr,
+					&(msgs[i+1].buf[1]), msgs[i+1].buf[0]);
+				if (result < 0) {
+					i = result;
+					goto error;
+				}
+			}
+
+			/* Eat up read message, too. */
+			i++;
+		} else if (msgs[i].flags & I2C_M_RD) {
+			/* Read transfer. */
+			result = w1_f19_i2c_read(sl, msgs[i].addr,
+				msgs[i].buf, msgs[i].len);
+			if (result < 0) {
+				i = result;
+				goto error;
+			}
+
+			/*
+			 * Check if we should interpret the read data
+			 * as a length byte. The DS28E17 unfortunately
+			 * has no read without stop, so we can just do
+			 * another simple read in that case.
+			 */
+			if (msgs[i].flags & I2C_M_RECV_LEN) {
+				result = w1_f19_i2c_read(sl,
+					msgs[i].addr,
+					&(msgs[i].buf[1]),
+					msgs[i].buf[0]);
+				if (result < 0) {
+					i = result;
+					goto error;
+				}
+			}
+		} else {
+			/*
+			 * Write transfer.
+			 * Stop condition only for last
+			 * transfer.
+			 */
+			result = w1_f19_i2c_write(sl,
+				msgs[i].addr,
+				msgs[i].buf,
+				msgs[i].len,
+				i == (num-1));
+			if (result < 0) {
+				i = result;
+				goto error;
+			}
+		}
+
+		/* Next message. */
+		i++;
+
+		/* Are there still messages to send/receive? */
+		if (i < num) {
+			/* Yes. Resume to same DS28E17. */
+			if (w1_reset_resume_command(sl->master)) {
+				i = -ENXIO;
+				goto error;
+			}
+		}
+	}
+
+error:
+	/* End onewire transaction. */
+	mutex_unlock(&sl->master->bus_mutex);
+
+	/* Return number of messages processed or error. */
+	return i;
+}
+
+
+/* Get I2C adapter functionality. */
+static u32 w1_f19_i2c_functionality(struct i2c_adapter *adapter)
+{
+	/*
+	 * Plain I2C functions only.
+	 * SMBus is emulated by the kernel's I2C layer.
+	 * No "I2C_FUNC_SMBUS_QUICK"
+	 * No "I2C_FUNC_SMBUS_READ_BLOCK_DATA"
+	 * No "I2C_FUNC_SMBUS_BLOCK_PROC_CALL"
+	 */
+	return I2C_FUNC_I2C |
+		I2C_FUNC_SMBUS_BYTE |
+		I2C_FUNC_SMBUS_BYTE_DATA |
+		I2C_FUNC_SMBUS_WORD_DATA |
+		I2C_FUNC_SMBUS_PROC_CALL |
+		I2C_FUNC_SMBUS_WRITE_BLOCK_DATA |
+		I2C_FUNC_SMBUS_I2C_BLOCK |
+		I2C_FUNC_SMBUS_PEC;
+}
+
+
+/* I2C algorithm. */
+static const struct i2c_algorithm w1_f19_i2c_algorithm = {
+	.master_xfer    = w1_f19_i2c_master_transfer,
+	.smbus_xfer     = NULL,
+	.functionality  = w1_f19_i2c_functionality,
+};
+
+
+/* I2C adapter quirks. */
+static const struct i2c_adapter_quirks w1_f19_i2c_adapter_quirks = {
+	.max_read_len = W1_F19_READ_DATA_LIMIT,
+};
+
+
+/* Read I2C speed from DS28E17. */
+static int w1_f19_get_i2c_speed(struct w1_slave *sl)
+{
+	struct w1_f19_data *data = sl->family_data;
+	int result = -ENXIO;
+
+	/* Start onewire transaction. */
+	mutex_lock(&sl->master->bus_mutex);
+
+	/* Select slave. */
+	if (w1_reset_select_slave(sl))
+		goto error;
+
+	/* Read slave configuration byte. */
+	w1_write_8(sl->master, W1_F19_READ_CONFIGURATION);
+	result = w1_read_8(sl->master);
+	if (result < 0 || result > 2) {
+		result = -EIO;
+		goto error;
+	}
+
+	/* Update speed in slave specific data. */
+	data->speed = result;
+
+error:
+	/* End onewire transaction. */
+	mutex_unlock(&sl->master->bus_mutex);
+
+	return result;
+}
+
+
+/* Set I2C speed on DS28E17. */
+static int __w1_f19_set_i2c_speed(struct w1_slave *sl, u8 speed)
+{
+	struct w1_f19_data *data = sl->family_data;
+	const int i2c_speeds[3] = { 100, 400, 900 };
+	u8 w1_buf[2];
+
+	/* Select slave. */
+	if (w1_reset_select_slave(sl))
+		return -ENXIO;
+
+	w1_buf[0] = W1_F19_WRITE_CONFIGURATION;
+	w1_buf[1] = speed;
+	w1_write_block(sl->master, w1_buf, 2);
+
+	/* Update speed in slave specific data. */
+	data->speed = speed;
+
+	dev_info(&sl->dev, "i2c speed set to %d kBaud\n", i2c_speeds[speed]);
+
+	return 0;
+}
+
+static int w1_f19_set_i2c_speed(struct w1_slave *sl, u8 speed)
+{
+	int result;
+
+	/* Start onewire transaction. */
+	mutex_lock(&sl->master->bus_mutex);
+
+	/* Set I2C speed on DS28E17. */
+	result = __w1_f19_set_i2c_speed(sl, speed);
+
+	/* End onewire transaction. */
+	mutex_unlock(&sl->master->bus_mutex);
+
+	return result;
+}
+
+
+/* Sysfs attributes. */
+
+/* I2C speed attribute for a single chip. */
+static ssize_t speed_show(struct device *dev, struct device_attribute *attr,
+			     char *buf)
+{
+	struct w1_slave *sl = dev_to_w1_slave(dev);
+	int result;
+
+	/* Read current speed from slave. Updates data->speed. */
+	result = w1_f19_get_i2c_speed(sl);
+	if (result < 0)
+		return result;
+
+	/* Return current speed value. */
+	return sprintf(buf, "%d\n", result);
+}
+
+static ssize_t speed_store(struct device *dev, struct device_attribute *attr,
+			      const char *buf, size_t count)
+{
+	struct w1_slave *sl = dev_to_w1_slave(dev);
+	int error;
+
+	/* Valid values are: '0' (100kHz), '1' (400kHz), '2' (900kHz) */
+	if (count < 1 || count > 2 || !buf)
+		return -EINVAL;
+	if (count == 2 && buf[1] != '\n')
+		return -EINVAL;
+	if (buf[0] != '0' && buf[0] != '1' && buf[0] != '2')
+		return -EINVAL;
+
+	/* Set speed on slave. */
+	error = w1_f19_set_i2c_speed(sl, buf[0] & 0x03);
+	if (error < 0)
+		return error;
+
+	/* Return bytes written. */
+	return count;
+}
+
+static DEVICE_ATTR_RW(speed);
+
+
+/* Busy stretch attribute for a single chip. */
+static ssize_t stretch_show(struct device *dev, struct device_attribute *attr,
+			     char *buf)
+{
+	struct w1_slave *sl = dev_to_w1_slave(dev);
+	struct w1_f19_data *data = sl->family_data;
+
+	/* Return current stretch value. */
+	return sprintf(buf, "%d\n", data->stretch);
+}
+
+static ssize_t stretch_store(struct device *dev, struct device_attribute *attr,
+			      const char *buf, size_t count)
+{
+	struct w1_slave *sl = dev_to_w1_slave(dev);
+	struct w1_f19_data *data = sl->family_data;
+
+	/* Valid values are '1' to '9' */
+	if (count < 1 || count > 2 || !buf)
+		return -EINVAL;
+	if (count == 2 && buf[1] != '\n')
+		return -EINVAL;
+	if (buf[0] < '1' || buf[0] > '9')
+		return -EINVAL;
+
+	/* Set busy stretch value. */
+	data->stretch = buf[0] & 0x0F;
+
+	/* Return bytes written. */
+	return count;
+}
+
+static DEVICE_ATTR_RW(stretch);
+
+
+/* All attributes. */
+static struct attribute *w1_f19_attrs[] = {
+	&dev_attr_speed.attr,
+	&dev_attr_stretch.attr,
+	NULL,
+};
+
+static const struct attribute_group w1_f19_group = {
+	.attrs		= w1_f19_attrs,
+};
+
+static const struct attribute_group *w1_f19_groups[] = {
+	&w1_f19_group,
+	NULL,
+};
+
+
+/* Slave add and remove functions. */
+static int w1_f19_add_slave(struct w1_slave *sl)
+{
+	struct w1_f19_data *data = NULL;
+
+	/* Allocate memory for slave specific data. */
+	data = kzalloc(sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+	sl->family_data = data;
+
+	/* Setup default I2C speed on slave. */
+	if (i2c_speed == 0 || i2c_speed == 1 || i2c_speed == 2) {
+		__w1_f19_set_i2c_speed(sl, i2c_speed);
+	}	else {
+		/*
+		 * A module parameter of anything else than 0, 1, 2
+		 * means not to touch the speed of the DS28E17.
+		 * We assume 400kBaud.
+		 */
+		data->speed = 1;
+	}
+
+	/*
+	 * Setup default busy stretch
+	 * configuration for the DS28E17.
+	 */
+	data->stretch = i2c_stretch;
+
+	/* Setup I2C adapter. */
+	data->adapter.owner      = THIS_MODULE;
+	data->adapter.class      = 0;
+	data->adapter.algo       = &w1_f19_i2c_algorithm;
+	data->adapter.algo_data  = (void *) sl;
+	strcpy(data->adapter.name, "w1-");
+	strcat(data->adapter.name, sl->name);
+	data->adapter.dev.parent = &sl->dev;
+	data->adapter.quirks     = &w1_f19_i2c_adapter_quirks;
+
+	return i2c_add_adapter(&data->adapter);
+}
+
+static void w1_f19_remove_slave(struct w1_slave *sl)
+{
+	/* Delete I2C adapter. */
+	i2c_del_adapter(&(((struct w1_f19_data *)(sl->family_data))->adapter));
+
+	/* Free slave specific data. */
+	kfree(sl->family_data);
+	sl->family_data = NULL;
+}
+
+
+/* Declarations within the w1 subsystem. */
+static struct w1_family_ops w1_f19_fops = {
+	.add_slave = w1_f19_add_slave,
+	.remove_slave = w1_f19_remove_slave,
+	.groups = w1_f19_groups,
+};
+
+static struct w1_family w1_family_19 = {
+	.fid = W1_FAMILY_DS28E17,
+	.fops = &w1_f19_fops,
+};
+
+
+/* Module init and remove functions. */
+static int __init w1_f19_init(void)
+{
+	return w1_register_family(&w1_family_19);
+}
+
+static void __exit w1_f19_fini(void)
+{
+	w1_unregister_family(&w1_family_19);
+}
+
+module_init(w1_f19_init);
+module_exit(w1_f19_fini);
+
diff --git a/drivers/w1/w1_family.h b/drivers/w1/w1_family.h
index ed5dcb8..5016a76 100644
--- a/drivers/w1/w1_family.h
+++ b/drivers/w1/w1_family.h
@@ -31,6 +31,7 @@ 
 #define W1_FAMILY_SMEM_01	0x01
 #define W1_FAMILY_SMEM_81	0x81
 #define W1_THERM_DS18S20 	0x10
+#define W1_FAMILY_DS28E17	0x19
 #define W1_FAMILY_DS28E04	0x1C
 #define W1_COUNTER_DS2423	0x1D
 #define W1_THERM_DS1822  	0x22