[v8,1/1] gpio: add sloppy logic analyzer using polling

This is a sloppy logic analyzer using GPIOs. It comes with a script to
isolate a CPU for polling. While this is definitely not a production
level analyzer, it can be a helpful first view when remote debugging.
Read the documentation for details.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
---
 .../dev-tools/gpio-sloppy-logic-analyzer.rst  |  91 +++++
 Documentation/dev-tools/index.rst             |   1 +
 drivers/gpio/Kconfig                          |  17 +
 drivers/gpio/Makefile                         |   1 +
 drivers/gpio/gpio-sloppy-logic-analyzer.c     | 340 ++++++++++++++++++
 tools/gpio/gpio-sloppy-logic-analyzer         | 230 ++++++++++++
 6 files changed, 680 insertions(+)
 create mode 100644 Documentation/dev-tools/gpio-sloppy-logic-analyzer.rst
 create mode 100644 drivers/gpio/gpio-sloppy-logic-analyzer.c
 create mode 100755 tools/gpio/gpio-sloppy-logic-analyzer

On Tue, Mar 29, 2022 at 11:11:26AM +0200, Wolfram Sang wrote:
> This is a sloppy logic analyzer using GPIOs. It comes with a script to
> isolate a CPU for polling. While this is definitely not a production
> level analyzer, it can be a helpful first view when remote debugging.
> Read the documentation for details.

Good enough I think,
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

> Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
> ---
>  .../dev-tools/gpio-sloppy-logic-analyzer.rst  |  91 +++++
>  Documentation/dev-tools/index.rst             |   1 +
>  drivers/gpio/Kconfig                          |  17 +
>  drivers/gpio/Makefile                         |   1 +
>  drivers/gpio/gpio-sloppy-logic-analyzer.c     | 340 ++++++++++++++++++
>  tools/gpio/gpio-sloppy-logic-analyzer         | 230 ++++++++++++
>  6 files changed, 680 insertions(+)
>  create mode 100644 Documentation/dev-tools/gpio-sloppy-logic-analyzer.rst
>  create mode 100644 drivers/gpio/gpio-sloppy-logic-analyzer.c
>  create mode 100755 tools/gpio/gpio-sloppy-logic-analyzer
> 
> diff --git a/Documentation/dev-tools/gpio-sloppy-logic-analyzer.rst b/Documentation/dev-tools/gpio-sloppy-logic-analyzer.rst
> new file mode 100644
> index 000000000000..a9b1cd6c2fea
> --- /dev/null
> +++ b/Documentation/dev-tools/gpio-sloppy-logic-analyzer.rst
> @@ -0,0 +1,91 @@
> +=============================================
> +Linux Kernel GPIO based sloppy logic analyzer
> +=============================================
> +
> +:Author: Wolfram Sang
> +
> +Introduction
> +============
> +
> +This document briefly describes how to run the GPIO based in-kernel sloppy
> +logic analyzer running on an isolated CPU.
> +
> +The sloppy logic analyzer will utilize a few GPIO lines in input mode on a
> +system to rapidly sample these digital lines, which will, if the Nyquist
> +criteria is met, result in a time series log with approximate waveforms as they
> +appeared on these lines. One way to use it is to analyze external traffic
> +connected to these GPIO lines with wires (i.e. digital probes), acting as a
> +common logic analyzer.
> +
> +Another feature is to snoop on on-chip peripherals if the I/O cells of these
> +peripherals can be used in GPIO input mode at the same time as they are being
> +used as inputs or outputs for the peripheral. That means you could e.g. snoop
> +I2C traffic without any wiring (if your hardware supports it). In the pin
> +control subsystem such pin controllers are called "non-strict": a certain pin
> +can be used with a certain peripheral and as a GPIO input line at the same
> +time.
> +
> +Note that this is a last resort analyzer which can be affected by latencies,
> +non-deterministic code paths and non-maskable interrupts. It is called 'sloppy'
> +for a reason. However, for e.g. remote development, it may be useful to get a
> +first view and aid further debugging.
> +
> +Setup
> +=====
> +
> +Your kernel must have CONFIG_DEBUG_FS and CONFIG_CPUSETS enabled. Ideally, your
> +runtime environment does not utilize cpusets otherwise, then isolation of a CPU
> +core is easiest. If you do need cpusets, check that helper script for the
> +sloppy logic analyzer does not interfere with your other settings.
> +
> +Tell the kernel which GPIOs are used as probes. For a Device Tree based system,
> +you need to use the following bindings. Because these bindings are only for
> +debugging, there is no official schema::
> +
> +    i2c-analyzer {
> +            compatible = "gpio-sloppy-logic-analyzer";
> +            probe-gpios = <&gpio6 21 GPIO_OPEN_DRAIN>, <&gpio6 4 GPIO_OPEN_DRAIN>;
> +            probe-names = "SCL", "SDA";
> +    };
> +
> +Note that you must provide a name for every GPIO specified. Currently a
> +maximum of 8 probes are supported. 32 are likely possible but are not
> +implemented yet.
> +
> +Usage
> +=====
> +
> +The logic analyzer is configurable via files in debugfs. However, it is
> +strongly recommended to not use them directly, but to use the script
> +``tools/gpio/gpio-sloppy-logic-analyzer``. Besides checking parameters more
> +extensively, it will isolate the CPU core so you will have the least
> +disturbance while measuring.
> +
> +The script has a help option explaining the parameters. For the above DT
> +snippet which analyzes an I2C bus at 400kHz on a Renesas Salvator-XS board, the
> +following settings are used: The isolated CPU shall be CPU1 because it is a big
> +core in a big.LITTLE setup. Because CPU1 is the default, we don't need a
> +parameter. The bus speed is 400kHz. So, the sampling theorem says we need to
> +sample at least at 800kHz. However, falling edges of both signals in an I2C
> +start condition happen faster, so we need a higher sampling frequency, e.g.
> +``-s 1500000`` for 1.5MHz. Also, we don't want to sample right away but wait
> +for a start condition on an idle bus. So, we need to set a trigger to a falling
> +edge on SDA while SCL stays high, i.e. ``-t 1H+2F``. Last is the duration, let
> +us assume 15ms here which results in the parameter ``-d 15000``. So,
> +altogether::
> +
> +    gpio-sloppy-logic-analyzer -s 1500000 -t 1H+2F -d 15000
> +
> +Note that the process will return you back to the prompt but a sub-process is
> +still sampling in the background. Unless this has finished, you will not find a
> +result file in the current or specified directory. For the above example, we
> +will then need to trigger I2C communication::
> +
> +    i2cdetect -y -r <your bus number>
> +
> +Result is a .sr file to be consumed with PulseView or sigrok-cli from the free
> +`sigrok`_ project. It is a zip file which also contains the binary sample data
> +which may be consumed by other software. The filename is the logic analyzer
> +instance name plus a since-epoch timestamp.
> +
> +.. _sigrok: https://sigrok.org/
> diff --git a/Documentation/dev-tools/index.rst b/Documentation/dev-tools/index.rst
> index 4621eac290f4..552d26e70003 100644
> --- a/Documentation/dev-tools/index.rst
> +++ b/Documentation/dev-tools/index.rst
> @@ -33,6 +33,7 @@ Documentation/dev-tools/testing-overview.rst
>     kselftest
>     kunit/index
>     ktap
> +   gpio-sloppy-logic-analyzer
>  
>  
>  .. only::  subproject and html
> diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
> index 1c211b4c63be..2a75a3ffb0ef 100644
> --- a/drivers/gpio/Kconfig
> +++ b/drivers/gpio/Kconfig
> @@ -1691,4 +1691,21 @@ config GPIO_SIM
>  
>  endmenu
>  
> +menu "GPIO hardware hacking tools"
> +
> +config GPIO_SLOPPY_LOGIC_ANALYZER
> +	tristate "Sloppy GPIO logic analyzer"
> +	depends on (GPIOLIB || COMPILE_TEST) && CPUSETS && DEBUG_FS && EXPERT
> +	help
> +	  This option enables support for a sloppy logic analyzer using polled
> +	  GPIOs. Use the 'tools/gpio/gpio-sloppy-logic-analyzer' script with
> +	  this driver. The script will make it easier to use and will also
> +	  isolate a CPU for the polling task. Note that this is a last resort
> +	  analyzer which can be affected by latencies, non-deterministic code
> +	  paths, or NMIs. However, for e.g. remote development, it may be useful
> +	  to get a first view and aid further debugging.
> +
> +	  If this driver is built as a module it will be called
> +	  'gpio-sloppy-logic-analyzer'.
> +endmenu
>  endif
> diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
> index edbaa3cb343c..dca6a3398cf0 100644
> --- a/drivers/gpio/Makefile
> +++ b/drivers/gpio/Makefile
> @@ -135,6 +135,7 @@ obj-$(CONFIG_GPIO_SIFIVE)		+= gpio-sifive.o
>  obj-$(CONFIG_GPIO_SIM)			+= gpio-sim.o
>  obj-$(CONFIG_GPIO_SIOX)			+= gpio-siox.o
>  obj-$(CONFIG_GPIO_SL28CPLD)		+= gpio-sl28cpld.o
> +obj-$(CONFIG_GPIO_SLOPPY_LOGIC_ANALYZER) += gpio-sloppy-logic-analyzer.o
>  obj-$(CONFIG_GPIO_SODAVILLE)		+= gpio-sodaville.o
>  obj-$(CONFIG_GPIO_SPEAR_SPICS)		+= gpio-spear-spics.o
>  obj-$(CONFIG_GPIO_SPRD)			+= gpio-sprd.o
> diff --git a/drivers/gpio/gpio-sloppy-logic-analyzer.c b/drivers/gpio/gpio-sloppy-logic-analyzer.c
> new file mode 100644
> index 000000000000..b96800c866b9
> --- /dev/null
> +++ b/drivers/gpio/gpio-sloppy-logic-analyzer.c
> @@ -0,0 +1,340 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Sloppy logic analyzer using GPIOs (to be run on an isolated CPU)
> + *
> + * Use the 'gpio-sloppy-logic-analyzer' script in the 'tools/gpio' folder for
> + * easier usage and further documentation. Note that this is a last resort
> + * analyzer which can be affected by latencies and non-deterministic code
> + * paths. However, for e.g. remote development, it may be useful to get a first
> + * view and aid further debugging.
> + *
> + * Copyright (C) Wolfram Sang <wsa@sang-engineering.com>
> + * Copyright (C) Renesas Electronics Corporation
> + */
> +
> +#include <linux/ctype.h>
> +#include <linux/debugfs.h>
> +#include <linux/delay.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/init.h>
> +#include <linux/ktime.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/platform_device.h>
> +#include <linux/property.h>
> +#include <linux/slab.h>
> +#include <linux/sizes.h>
> +#include <linux/timekeeping.h>
> +#include <linux/vmalloc.h>
> +
> +#define GPIO_LA_NAME "gpio-sloppy-logic-analyzer"
> +#define GPIO_LA_DEFAULT_BUF_SIZE SZ_256K
> +/* can be increased but then we need to extend the u8 buffers */
> +#define GPIO_LA_MAX_PROBES 8
> +#define GPIO_LA_NUM_TESTS 1024
> +
> +struct gpio_la_poll_priv {
> +	struct mutex lock;
> +	u32 buf_idx;
> +	struct gpio_descs *descs;
> +	unsigned long delay_ns;
> +	unsigned long acq_delay;
> +	struct debugfs_blob_wrapper blob;
> +	struct dentry *debug_dir;
> +	struct dentry *blob_dent;
> +	struct debugfs_blob_wrapper meta;
> +	struct device *dev;
> +	unsigned int trig_len;
> +	u8 *trig_data;
> +};
> +
> +static struct dentry *gpio_la_poll_debug_dir;
> +
> +static __always_inline int gpio_la_get_array(struct gpio_descs *d, unsigned long *sptr)
> +{
> +	int ret;
> +
> +	ret = gpiod_get_array_value(d->ndescs, d->desc, d->info, sptr);
> +	if (ret == 0 && fatal_signal_pending(current))
> +		ret = -EINTR;
> +
> +	return ret;
> +}
> +
> +static int fops_capture_set(void *data, u64 val)
> +{
> +	struct gpio_la_poll_priv *priv = data;
> +	u8 *la_buf = priv->blob.data;
> +	unsigned long state = 0; /* zeroed because GPIO arrays are bitfields */
> +	unsigned long delay;
> +	ktime_t start_time;
> +	unsigned int i;
> +	int ret;
> +
> +	if (!val)
> +		return 0;
> +
> +	if (!la_buf)
> +		return -ENOMEM;
> +
> +	if (!priv->delay_ns)
> +		return -EINVAL;
> +
> +	mutex_lock(&priv->lock);
> +	if (priv->blob_dent) {
> +		debugfs_remove(priv->blob_dent);
> +		priv->blob_dent = NULL;
> +	}
> +
> +	priv->buf_idx = 0;
> +
> +	local_irq_disable();
> +	preempt_disable_notrace();
> +
> +	/* Measure delay of reading GPIOs */
> +	start_time = ktime_get();
> +	for (i = 0; i < GPIO_LA_NUM_TESTS; i++) {
> +		ret = gpio_la_get_array(priv->descs, &state);
> +		if (ret)
> +			goto out;
> +	}
> +
> +	priv->acq_delay = ktime_sub(ktime_get(), start_time) / GPIO_LA_NUM_TESTS;
> +	if (priv->delay_ns < priv->acq_delay) {
> +		ret = -ERANGE;
> +		goto out;
> +	}
> +
> +	delay = priv->delay_ns - priv->acq_delay;
> +
> +	/* Wait for triggers */
> +	for (i = 0; i < priv->trig_len; i += 2) {
> +		do {
> +			ret = gpio_la_get_array(priv->descs, &state);
> +			if (ret)
> +				goto out;
> +
> +			ndelay(delay);
> +		} while ((state & priv->trig_data[i]) != priv->trig_data[i + 1]);
> +	}
> +
> +	/* With triggers, final state is also the first sample */
> +	if (priv->trig_len)
> +		la_buf[priv->buf_idx++] = state;
> +
> +	/* Sample */
> +	while (priv->buf_idx < priv->blob.size) {
> +		ret = gpio_la_get_array(priv->descs, &state);
> +		if (ret)
> +			goto out;
> +
> +		la_buf[priv->buf_idx++] = state;
> +		ndelay(delay);
> +	}
> +out:
> +	preempt_enable_notrace();
> +	local_irq_enable();
> +	if (ret)
> +		dev_err(priv->dev, "couldn't read GPIOs: %d\n", ret);
> +
> +	kfree(priv->trig_data);
> +	priv->trig_data = NULL;
> +	priv->trig_len = 0;
> +
> +	priv->blob_dent = debugfs_create_blob("sample_data", 0400, priv->debug_dir, &priv->blob);
> +	mutex_unlock(&priv->lock);
> +
> +	return ret;
> +}
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_capture, NULL, fops_capture_set, "%llu\n");
> +
> +static int fops_buf_size_get(void *data, u64 *val)
> +{
> +	struct gpio_la_poll_priv *priv = data;
> +
> +	*val = priv->blob.size;
> +
> +	return 0;
> +}
> +
> +static int fops_buf_size_set(void *data, u64 val)
> +{
> +	struct gpio_la_poll_priv *priv = data;
> +	int ret = 0;
> +	void *p;
> +
> +	if (!val)
> +		return -EINVAL;
> +
> +	mutex_lock(&priv->lock);
> +
> +	vfree(priv->blob.data);
> +	p = vzalloc(val);
> +	if (!p) {
> +		val = 0;
> +		ret = -ENOMEM;
> +	}
> +
> +	priv->blob.data = p;
> +	priv->blob.size = val;
> +
> +	mutex_unlock(&priv->lock);
> +	return ret;
> +}
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_buf_size, fops_buf_size_get, fops_buf_size_set, "%llu\n");
> +
> +static int trigger_open(struct inode *inode, struct file *file)
> +{
> +	return single_open(file, NULL, inode->i_private);
> +}
> +
> +static ssize_t trigger_write(struct file *file, const char __user *ubuf,
> +			     size_t count, loff_t *offset)
> +{
> +	struct seq_file *m = file->private_data;
> +	struct gpio_la_poll_priv *priv = m->private;
> +	char *buf;
> +
> +	/* upper limit is arbitrary but should be less than PAGE_SIZE */
> +	if (count > 2048 || count & 1)
> +		return -EINVAL;
> +
> +	buf = memdup_user(ubuf, count);
> +	if (IS_ERR(buf))
> +		return PTR_ERR(buf);
> +
> +	priv->trig_data = buf;
> +	priv->trig_len = count;
> +
> +	return count;
> +}
> +
> +static const struct file_operations fops_trigger = {
> +	.owner = THIS_MODULE,
> +	.open = trigger_open,
> +	.write = trigger_write,
> +	.llseek = no_llseek,
> +	.release = single_release,
> +};
> +
> +static int gpio_la_poll_probe(struct platform_device *pdev)
> +{
> +	struct gpio_la_poll_priv *priv;
> +	struct device *dev = &pdev->dev;
> +	const char *devname = dev_name(dev);
> +	const char *gpio_names[GPIO_LA_MAX_PROBES];
> +	char *meta = NULL;
> +	unsigned int i, meta_len = 0;
> +	int ret;
> +
> +	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
> +	mutex_init(&priv->lock);
> +
> +	fops_buf_size_set(priv, GPIO_LA_DEFAULT_BUF_SIZE);
> +
> +	priv->descs = devm_gpiod_get_array(dev, "probe", GPIOD_IN);
> +	if (IS_ERR(priv->descs))
> +		return PTR_ERR(priv->descs);
> +
> +	/* artificial limit to keep 1 byte per sample for now */
> +	if (priv->descs->ndescs > GPIO_LA_MAX_PROBES)
> +		return -EFBIG;
> +
> +	ret = device_property_read_string_array(dev, "probe-names", gpio_names,
> +						priv->descs->ndescs);
> +	if (ret >= 0 && ret != priv->descs->ndescs)
> +		ret = -EBADR;
> +	if (ret < 0)
> +		return dev_err_probe(dev, ret, "error naming the GPIOs");
> +
> +	for (i = 0; i < priv->descs->ndescs; i++) {
> +		unsigned int add_len;
> +		char *new_meta, *consumer_name;
> +
> +		if (gpiod_cansleep(priv->descs->desc[i]))
> +			return -EREMOTE;
> +
> +		consumer_name = kasprintf(GFP_KERNEL, "%s: %s", devname, gpio_names[i]);
> +		if (!consumer_name)
> +			return -ENOMEM;
> +		gpiod_set_consumer_name(priv->descs->desc[i], consumer_name);
> +		kfree(consumer_name);
> +
> +		/* '10' is length of 'probe00=\n\0' */
> +		add_len = strlen(gpio_names[i]) + 10;
> +
> +		new_meta = devm_krealloc(dev, meta, meta_len + add_len, GFP_KERNEL);
> +		if (!new_meta)
> +			return -ENOMEM;
> +
> +		meta = new_meta;
> +		meta_len += snprintf(meta + meta_len, add_len, "probe%02u=%s\n",
> +				     i + 1, gpio_names[i]);
> +	}
> +
> +	platform_set_drvdata(pdev, priv);
> +	priv->dev = dev;
> +
> +	priv->meta.data = meta;
> +	priv->meta.size = meta_len;
> +	priv->debug_dir = debugfs_create_dir(devname, gpio_la_poll_debug_dir);
> +	debugfs_create_blob("meta_data", 0400, priv->debug_dir, &priv->meta);
> +	debugfs_create_ulong("delay_ns", 0600, priv->debug_dir, &priv->delay_ns);
> +	debugfs_create_ulong("delay_ns_acquisition", 0400, priv->debug_dir, &priv->acq_delay);
> +	debugfs_create_file_unsafe("buf_size", 0600, priv->debug_dir, priv, &fops_buf_size);
> +	debugfs_create_file_unsafe("capture", 0200, priv->debug_dir, priv, &fops_capture);
> +	debugfs_create_file_unsafe("trigger", 0200, priv->debug_dir, priv, &fops_trigger);
> +
> +	dev_info(dev, "initialized");
> +	return 0;
> +}
> +
> +static int gpio_la_poll_remove(struct platform_device *pdev)
> +{
> +	struct gpio_la_poll_priv *priv = platform_get_drvdata(pdev);
> +
> +	mutex_lock(&priv->lock);
> +	debugfs_remove_recursive(priv->debug_dir);
> +	mutex_unlock(&priv->lock);
> +	mutex_destroy(&priv->lock);
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id gpio_la_poll_of_match[] = {
> +	{ .compatible = GPIO_LA_NAME, },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(of, gpio_la_poll_of_match);
> +
> +static struct platform_driver gpio_la_poll_device_driver = {
> +	.probe = gpio_la_poll_probe,
> +	.remove = gpio_la_poll_remove,
> +	.driver = {
> +		.name = GPIO_LA_NAME,
> +		.of_match_table = gpio_la_poll_of_match,
> +	}
> +};
> +
> +static int __init gpio_la_poll_init(void)
> +{
> +	gpio_la_poll_debug_dir = debugfs_create_dir(GPIO_LA_NAME, NULL);
> +
> +	return platform_driver_register(&gpio_la_poll_device_driver);
> +}
> +late_initcall(gpio_la_poll_init);
> +
> +static void __exit gpio_la_poll_exit(void)
> +{
> +	platform_driver_unregister(&gpio_la_poll_device_driver);
> +	debugfs_remove_recursive(gpio_la_poll_debug_dir);
> +}
> +module_exit(gpio_la_poll_exit);
> +
> +MODULE_AUTHOR("Wolfram Sang <wsa@sang-engineering.com>");
> +MODULE_DESCRIPTION("Sloppy logic analyzer using GPIOs");
> +MODULE_LICENSE("GPL v2");
> diff --git a/tools/gpio/gpio-sloppy-logic-analyzer b/tools/gpio/gpio-sloppy-logic-analyzer
> new file mode 100755
> index 000000000000..09065535e874
> --- /dev/null
> +++ b/tools/gpio/gpio-sloppy-logic-analyzer
> @@ -0,0 +1,230 @@
> +#!/bin/sh -eu
> +# Helper script for the Linux Kernel GPIO sloppy logic analyzer
> +#
> +# Copyright (C) Wolfram Sang <wsa@sang-engineering.com>
> +# Copyright (C) Renesas Electronics Corporation
> +#
> +# TODO: support SI units in command line parameters?
> +
> +samplefreq=1000000
> +numsamples=250000
> +cpusetdefaultdir='/sys/fs/cgroup'
> +cpusetprefix='cpuset.'
> +debugdir='/sys/kernel/debug'
> +ladirname='gpio-sloppy-logic-analyzer'
> +outputdir="$PWD"
> +neededcmds='taskset zip'
> +max_chans=8
> +duration=
> +initcpu=
> +lainstance=
> +lasysfsdir=
> +triggerdat=
> +trigger_bindat=
> +progname="${0##*/}"
> +print_help()
> +{
> +	cat << EOF
> +$progname - helper script for the Linux Kernel Sloppy GPIO Logic Analyzer
> +Available options:
> +	-c|--cpu <n>: which CPU to isolate for sampling. Only needed once. Default <1>.
> +		      Remember that a more powerful CPU gives you higher sampling speeds.
> +		      Also CPU0 is not recommended as it usually does extra bookkeeping.
> +	-d|--duration-us <n>: number of microseconds to sample. Overrides -n, no default value.
> +	-h|--help: print this help
> +	-i|--instance <str>: name of the logic analyzer in case you have multiple instances. Default
> +			     to first instance found
> +	-k|--kernel-debug-dir: path to the kernel debugfs mountpoint. Default: <$debugdir>
> +	-n|--num_samples <n>: number of samples to acquire. Default <$numsamples>
> +	-o|--output-dir <str>: directory to put the result files. Default: current dir
> +	-s|--sample_freq <n>: desired sampling frequency. Might be capped if too large. Default: 1MHz.
> +	-t|--trigger <str>: pattern to use as trigger. <str> consists of two-char pairs. First
> +			    char is channel number starting at "1". Second char is trigger level:
> +			    "L" - low; "H" - high; "R" - rising; "F" - falling
> +			    These pairs can be combined with "+", so "1H+2F" triggers when probe 1
> +			    is high while probe 2 has a falling edge. You can have multiple triggers
> +			    combined with ",". So, "1H+2F,1H+2R" is like the example before but it
> +			    waits for a rising edge on probe 2 while probe 1 is still high after the
> +			    first trigger has been met.
> +			    Trigger data will only be used for the next capture and then be erased.
> +Examples:
> +Samples $numsamples values at 1MHz with an already prepared CPU or automatically prepares CPU1 if needed,
> +use the first logic analyzer instance found:
> +	'$progname'
> +Samples 50us at 2MHz waiting for a falling edge on channel 2. CPU and instance as above:
> +	'$progname -d 50 -s 2000000 -t "2F"'
> +
> +Note that the process exits after checking all parameters but a sub-process still works in
> +the background. The result is only available once the sub-process finishes.
> +
> +Result is a .sr file to be consumed with PulseView from the free Sigrok project. It is
> +a zip file which also contains the binary sample data which may be consumed by others.
> +The filename is the logic analyzer instance name plus a since-epoch timestamp.
> +EOF
> +}
> +
> +fail()
> +{
> +	echo "$1"
> +	exit 1
> +}
> +
> +set_newmask()
> +{
> +	for f in $(find "$1" -iname "$2"); do echo "$newmask" > "$f" 2>/dev/null || true; done
> +}
> +
> +init_cpu()
> +{
> +	isol_cpu="$1"
> +
> +	[ -d "$lacpusetdir" ] || mkdir "$lacpusetdir"
> +
> +	cur_cpu=$(cat "${lacpusetfile}cpus")
> +	[ "$cur_cpu" = "$isol_cpu" ] && return
> +	[ -z "$cur_cpu" ] || fail "CPU$isol_cpu requested but CPU$cur_cpu already isolated"
> +
> +	echo "$isol_cpu" > "${lacpusetfile}cpus" || fail "Could not isolate CPU$isol_cpu. Does it exist?"
> +	echo 1 > "${lacpusetfile}cpu_exclusive"
> +	echo 0 > "${lacpusetfile}mems"
> +
> +	oldmask=$(cat /proc/irq/default_smp_affinity)
> +	newmask=$(printf "%x" $((0x$oldmask & ~(1 << isol_cpu))))
> +
> +	set_newmask '/proc/irq' '*smp_affinity'
> +	set_newmask '/sys/devices/virtual/workqueue/' 'cpumask'
> +
> +	# Move tasks away from isolated CPU
> +	for p in $(ps -o pid | tail -n +2); do
> +		mask=$(taskset -p "$p") || continue
> +		# Ignore tasks with a custom mask, i.e. not equal $oldmask
> +		[ "${mask##*: }" = "$oldmask" ] || continue
> +		taskset -p "$newmask" "$p" || continue
> +	done 2>/dev/null >/dev/null
> +
> +	echo 1 > /sys/module/rcupdate/parameters/rcu_cpu_stall_suppress
> +
> +	cpufreqgov="/sys/devices/system/cpu/cpu$isol_cpu/cpufreq/scaling_governor"
> +	[ -w "$cpufreqgov" ] && echo 'performance' > "$cpufreqgov" || true
> +}
> +
> +parse_triggerdat()
> +{
> +	oldifs="$IFS"
> +	IFS=','; for trig in $1; do
> +		mask=0; val1=0; val2=0
> +		IFS='+'; for elem in $trig; do
> +			chan=${elem%[lhfrLHFR]}
> +			mode=${elem#$chan}
> +			# Check if we could parse something and the channel number fits
> +			[ "$chan" != "$elem" ] && [ "$chan" -le $max_chans ] || fail "Trigger syntax error: $elem"
> +			bit=$((1 << (chan - 1)))
> +			mask=$((mask | bit))
> +			case $mode in
> +				[hH]) val1=$((val1 | bit)); val2=$((val2 | bit));;
> +				[fF]) val1=$((val1 | bit));;
> +				[rR]) val2=$((val2 | bit));;
> +			esac
> +		done
> +		trigger_bindat="$trigger_bindat$(printf '\\%o\\%o' $mask $val1)"
> +		[ $val1 -ne $val2 ] && trigger_bindat="$trigger_bindat$(printf '\\%o\\%o' $mask $val2)"
> +	done
> +	IFS="$oldifs"
> +}
> +
> +do_capture()
> +{
> +	taskset "$1" echo 1 > "$lasysfsdir"/capture || fail "Capture error! Check kernel log"
> +
> +	srtmp=$(mktemp -d)
> +	echo 1 > "$srtmp"/version
> +	cp "$lasysfsdir"/sample_data "$srtmp"/logic-1-1
> +	cat > "$srtmp"/metadata << EOF
> +[global]
> +sigrok version=0.2.0
> +
> +[device 1]
> +capturefile=logic-1
> +total probes=$(wc -l < "$lasysfsdir"/meta_data)
> +samplerate=${samplefreq}Hz
> +unitsize=1
> +EOF
> +	cat "$lasysfsdir"/meta_data >> "$srtmp"/metadata
> +
> +	zipname="$outputdir/${lasysfsdir##*/}-$(date +%s).sr"
> +	zip -jq "$zipname" "$srtmp"/*
> +	rm -rf "$srtmp"
> +	delay_ack=$(cat "$lasysfsdir"/delay_ns_acquisition)
> +	[ "$delay_ack" -eq 0 ] && delay_ack=1
> +	echo "Logic analyzer done. Saved '$zipname'"
> +	echo "Max sample frequency this time: $((1000000000 / delay_ack))Hz."
> +}
> +
> +rep=$(getopt -a -l cpu:,duration-us:,help,instance:,kernel-debug-dir:,num_samples:,output-dir:,sample_freq:,trigger: -o c:d:hi:k:n:o:s:t: -- "$@") || exit 1
> +eval set -- "$rep"
> +while true; do
> +	case "$1" in
> +	-c|--cpu) initcpu="$2"; shift;;
> +	-d|--duration-us) duration="$2"; shift;;
> +	-h|--help) print_help; exit 0;;
> +	-i|--instance) lainstance="$2"; shift;;
> +	-k|--kernel-debug-dir) debugdir="$2"; shift;;
> +	-n|--num_samples) numsamples="$2"; shift;;
> +	-o|--output-dir) outputdir="$2"; shift;;
> +	-s|--sample_freq) samplefreq="$2"; shift;;
> +	-t|--trigger) triggerdat="$2"; shift;;
> +	--) break;;
> +	*) fail "error parsing command line: $*";;
> +	esac
> +	shift
> +done
> +
> +for f in $neededcmds; do
> +	command -v "$f" >/dev/null || fail "Command '$f' not found"
> +done
> +
> +# print cpuset mountpoint if any, errorcode > 0 if noprefix option was found
> +cpusetdir=$(awk '$3 == "cgroup" && $4 ~ /cpuset/ { print $2; exit (match($4, /noprefix/) > 0) }' /proc/self/mounts) || cpusetprefix=''
> +if [ -z "$cpusetdir" ]; then
> +	cpusetdir="$cpusetdefaultdir"
> +	[ -d $cpusetdir ] || mkdir $cpusetdir
> +	mount -t cgroup -o cpuset none $cpusetdir || fail "Couldn't mount cpusets. Not in kernel or already in use?"
> +fi
> +
> +lacpusetdir="$cpusetdir/$ladirname"
> +lacpusetfile="$lacpusetdir/$cpusetprefix"
> +sysfsdir="$debugdir/$ladirname"
> +
> +[ "$samplefreq" -ne 0 ] || fail "Invalid sample frequency"
> +
> +[ -d "$sysfsdir" ] || fail "Could not find logic analyzer root dir '$sysfsdir'. Module loaded?"
> +[ -x "$sysfsdir" ] || fail "Could not access logic analyzer root dir '$sysfsdir'. Need root?"
> +
> +if [ -n "$lainstance" ]; then
> +	lasysfsdir="$sysfsdir/$lainstance"
> +else
> +	lasysfsdir=$(find "$sysfsdir" -mindepth 1 -type d -print -quit)
> +fi
> +[ -d "$lasysfsdir" ] || fail "Logic analyzer directory '$lasysfsdir' not found!"
> +[ -d "$outputdir" ] || fail "Output directory '$outputdir' not found!"
> +
> +[ -n "$initcpu" ] && init_cpu "$initcpu"
> +[ -d "$lacpusetdir" ] || { echo "Auto-Isolating CPU1"; init_cpu 1; }
> +
> +ndelay=$((1000000000 / samplefreq))
> +echo "$ndelay" > "$lasysfsdir"/delay_ns
> +
> +[ -n "$duration" ] && numsamples=$((samplefreq * duration / 1000000))
> +echo $numsamples > "$lasysfsdir"/buf_size
> +
> +if [ -n "$triggerdat" ]; then
> +	parse_triggerdat "$triggerdat"
> +	printf "$trigger_bindat" > "$lasysfsdir"/trigger 2>/dev/null || fail "Trigger data '$triggerdat' rejected"
> +fi
> +
> +workcpu=$(cat "${lacpusetfile}effective_cpus")
> +[ -n "$workcpu" ] || fail "No isolated CPU found"
> +cpumask=$(printf '%x' $((1 << workcpu)))
> +instance=${lasysfsdir##*/}
> +echo "Setting up '$instance': $numsamples samples at ${samplefreq}Hz with ${triggerdat:-no} trigger using CPU$workcpu"
> +do_capture "$cpumask" &
> -- 
> 2.30.2
>

On Wed, Mar 30, 2022 at 05:51:10PM +0300, Andy Shevchenko wrote:
> On Tue, Mar 29, 2022 at 11:11:26AM +0200, Wolfram Sang wrote:
> > This is a sloppy logic analyzer using GPIOs. It comes with a script to
> > isolate a CPU for polling. While this is definitely not a production
> > level analyzer, it can be a helpful first view when remote debugging.
> > Read the documentation for details.
> 
> Good enough I think,
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

Thanks, Andy!

To GPIO maintainers: can we apply the "new-driver-rule" and still have
it in 5.19? There can't be any regression and it has all comments
addressed. Also, I am talking about this project at Kernel Recipes late
next week and it would be great to say that it is finally merged :)

All the best,


   Wolfram

On Wed, May 25, 2022 at 05:07:39PM +0200, Wolfram Sang wrote:
> On Wed, Mar 30, 2022 at 05:51:10PM +0300, Andy Shevchenko wrote:
> > On Tue, Mar 29, 2022 at 11:11:26AM +0200, Wolfram Sang wrote:
> > > This is a sloppy logic analyzer using GPIOs. It comes with a script to
> > > isolate a CPU for polling. While this is definitely not a production
> > > level analyzer, it can be a helpful first view when remote debugging.
> > > Read the documentation for details.
> > 
> > Good enough I think,
> > Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> 
> Thanks, Andy!
> 
> To GPIO maintainers: can we apply the "new-driver-rule" and still have
> it in 5.19? There can't be any regression and it has all comments
> addressed. Also, I am talking about this project at Kernel Recipes late
> next week and it would be great to say that it is finally merged :)

Year passed. Any news here?

On Thu, Jun 01, 2023 at 06:58:15PM +0300, Andy Shevchenko wrote:
> On Wed, May 25, 2022 at 05:07:39PM +0200, Wolfram Sang wrote:
> > On Wed, Mar 30, 2022 at 05:51:10PM +0300, Andy Shevchenko wrote:
> > > On Tue, Mar 29, 2022 at 11:11:26AM +0200, Wolfram Sang wrote:
> > > > This is a sloppy logic analyzer using GPIOs. It comes with a script to
> > > > isolate a CPU for polling. While this is definitely not a production
> > > > level analyzer, it can be a helpful first view when remote debugging.
> > > > Read the documentation for details.
> > > 
> > > Good enough I think,
> > > Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > 
> > Thanks, Andy!
> > 
> > To GPIO maintainers: can we apply the "new-driver-rule" and still have
> > it in 5.19? There can't be any regression and it has all comments
> > addressed. Also, I am talking about this project at Kernel Recipes late
> > next week and it would be great to say that it is finally merged :)
> 
> Year passed. Any news here?

Ah, GPIO maintainers probably missed this since no Cc.

Tue, Mar 29, 2022 at 11:11:26AM +0200, Wolfram Sang kirjoitti:
> This is a sloppy logic analyzer using GPIOs. It comes with a script to
> isolate a CPU for polling. While this is definitely not a production
> level analyzer, it can be a helpful first view when remote debugging.
> Read the documentation for details.

One note since I have done recent review and realize one issue with debugfs.

...

> +	priv->debug_dir = debugfs_create_dir(devname, gpio_la_poll_debug_dir);

If this fails with NULL...

> +	debugfs_create_blob("meta_data", 0400, priv->debug_dir, &priv->meta);
> +	debugfs_create_ulong("delay_ns", 0600, priv->debug_dir, &priv->delay_ns);
> +	debugfs_create_ulong("delay_ns_acquisition", 0400, priv->debug_dir, &priv->acq_delay);
> +	debugfs_create_file_unsafe("buf_size", 0600, priv->debug_dir, priv, &fops_buf_size);
> +	debugfs_create_file_unsafe("capture", 0200, priv->debug_dir, priv, &fops_capture);
> +	debugfs_create_file_unsafe("trigger", 0200, priv->debug_dir, priv, &fops_trigger);

...and any of these is not, we will end up with the file in a root folder of debugfs...

> +	dev_info(dev, "initialized");

...

> +static int gpio_la_poll_remove(struct platform_device *pdev)
> +{
> +	struct gpio_la_poll_priv *priv = platform_get_drvdata(pdev);
> +
> +	mutex_lock(&priv->lock);
> +	debugfs_remove_recursive(priv->debug_dir);

...and this one won't remove it.

> +	mutex_unlock(&priv->lock);
> +	mutex_destroy(&priv->lock);
> +
> +	return 0;
> +}

...

However, I haven't checked if it's pure theoretical issue with the current code
base of debugfs or a potential problem. Easy fix is to check an error code and
skip the files creation. Not sure if driver will be useful in that case.

Hi Andy,

CC GregKH

On Thu, Jun 1, 2023 at 11:40 PM <andy.shevchenko@gmail.com> wrote:
> Tue, Mar 29, 2022 at 11:11:26AM +0200, Wolfram Sang kirjoitti:
> > This is a sloppy logic analyzer using GPIOs. It comes with a script to
> > isolate a CPU for polling. While this is definitely not a production
> > level analyzer, it can be a helpful first view when remote debugging.
> > Read the documentation for details.
>
> One note since I have done recent review and realize one issue with debugfs.
>
> ...
>
> > +     priv->debug_dir = debugfs_create_dir(devname, gpio_la_poll_debug_dir);
>
> If this fails with NULL...
>
> > +     debugfs_create_blob("meta_data", 0400, priv->debug_dir, &priv->meta);
> > +     debugfs_create_ulong("delay_ns", 0600, priv->debug_dir, &priv->delay_ns);
> > +     debugfs_create_ulong("delay_ns_acquisition", 0400, priv->debug_dir, &priv->acq_delay);
> > +     debugfs_create_file_unsafe("buf_size", 0600, priv->debug_dir, priv, &fops_buf_size);
> > +     debugfs_create_file_unsafe("capture", 0200, priv->debug_dir, priv, &fops_capture);
> > +     debugfs_create_file_unsafe("trigger", 0200, priv->debug_dir, priv, &fops_trigger);
>
> ...and any of these is not, we will end up with the file in a root folder of debugfs...
>
> > +     dev_info(dev, "initialized");
>
> ...
>
> > +static int gpio_la_poll_remove(struct platform_device *pdev)
> > +{
> > +     struct gpio_la_poll_priv *priv = platform_get_drvdata(pdev);
> > +
> > +     mutex_lock(&priv->lock);
> > +     debugfs_remove_recursive(priv->debug_dir);
>
> ...and this one won't remove it.
>
> > +     mutex_unlock(&priv->lock);
> > +     mutex_destroy(&priv->lock);
> > +
> > +     return 0;
> > +}
>
> ...
>
> However, I haven't checked if it's pure theoretical issue with the current code
> base of debugfs or a potential problem. Easy fix is to check an error code and

I think debugfs_create_dir() can only fail reasonably due to OOM.

> skip the files creation. Not sure if driver will be useful in that case.

Having to add such error checks would really be unfortunate, because
one of the design principles of debugfs is that there is never a need
to check for errors.

Gr{oetje,eeting}s,

                        Geert

On Fri, Jun 2, 2023 at 8:51 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> On Thu, Jun 1, 2023 at 11:40 PM <andy.shevchenko@gmail.com> wrote:
> > Tue, Mar 29, 2022 at 11:11:26AM +0200, Wolfram Sang kirjoitti:
> > > This is a sloppy logic analyzer using GPIOs. It comes with a script to
> > > isolate a CPU for polling. While this is definitely not a production
> > > level analyzer, it can be a helpful first view when remote debugging.
> > > Read the documentation for details.
> >
> > One note since I have done recent review and realize one issue with debugfs.
> >
> > ...
> >
> > > +     priv->debug_dir = debugfs_create_dir(devname, gpio_la_poll_debug_dir);
> >
> > If this fails with NULL...
> >
> > > +     debugfs_create_blob("meta_data", 0400, priv->debug_dir, &priv->meta);
> > > +     debugfs_create_ulong("delay_ns", 0600, priv->debug_dir, &priv->delay_ns);
> > > +     debugfs_create_ulong("delay_ns_acquisition", 0400, priv->debug_dir, &priv->acq_delay);
> > > +     debugfs_create_file_unsafe("buf_size", 0600, priv->debug_dir, priv, &fops_buf_size);
> > > +     debugfs_create_file_unsafe("capture", 0200, priv->debug_dir, priv, &fops_capture);
> > > +     debugfs_create_file_unsafe("trigger", 0200, priv->debug_dir, priv, &fops_trigger);
> >
> > ...and any of these is not, we will end up with the file in a root folder of debugfs...
> >
> > > +     dev_info(dev, "initialized");
> >
> > ...
> >
> > > +static int gpio_la_poll_remove(struct platform_device *pdev)
> > > +{
> > > +     struct gpio_la_poll_priv *priv = platform_get_drvdata(pdev);
> > > +
> > > +     mutex_lock(&priv->lock);
> > > +     debugfs_remove_recursive(priv->debug_dir);
> >
> > ...and this one won't remove it.
> >
> > > +     mutex_unlock(&priv->lock);
> > > +     mutex_destroy(&priv->lock);
> > > +
> > > +     return 0;
> > > +}
> >
> > ...
> >
> > However, I haven't checked if it's pure theoretical issue with the current code
> > base of debugfs or a potential problem. Easy fix is to check an error code and
>
> I think debugfs_create_dir() can only fail reasonably due to OOM.

Oops, you were talking about NULL, not an error code.
I don't think that can ever happen.
And if I did miss something, it would crash when dereferencing a NULL
pointer in d_really_is_positive() (as called in start_creating())...

Gr{oetje,eeting}s,

                        Geert

On Fri, Jun 02, 2023 at 08:51:50AM +0200, Geert Uytterhoeven wrote:
> Hi Andy,
> 
> CC GregKH
> 
> On Thu, Jun 1, 2023 at 11:40 PM <andy.shevchenko@gmail.com> wrote:
> > Tue, Mar 29, 2022 at 11:11:26AM +0200, Wolfram Sang kirjoitti:
> > > This is a sloppy logic analyzer using GPIOs. It comes with a script to
> > > isolate a CPU for polling. While this is definitely not a production
> > > level analyzer, it can be a helpful first view when remote debugging.
> > > Read the documentation for details.
> >
> > One note since I have done recent review and realize one issue with debugfs.
> >
> > ...
> >
> > > +     priv->debug_dir = debugfs_create_dir(devname, gpio_la_poll_debug_dir);
> >
> > If this fails with NULL...
> >
> > > +     debugfs_create_blob("meta_data", 0400, priv->debug_dir, &priv->meta);
> > > +     debugfs_create_ulong("delay_ns", 0600, priv->debug_dir, &priv->delay_ns);
> > > +     debugfs_create_ulong("delay_ns_acquisition", 0400, priv->debug_dir, &priv->acq_delay);
> > > +     debugfs_create_file_unsafe("buf_size", 0600, priv->debug_dir, priv, &fops_buf_size);
> > > +     debugfs_create_file_unsafe("capture", 0200, priv->debug_dir, priv, &fops_capture);
> > > +     debugfs_create_file_unsafe("trigger", 0200, priv->debug_dir, priv, &fops_trigger);
> >
> > ...and any of these is not, we will end up with the file in a root folder of debugfs...
> >
> > > +     dev_info(dev, "initialized");

Nit, please remove this line.  Drivers are quiet when they work
properly, don't add to a mess in the kernel log.

> > ...
> >
> > > +static int gpio_la_poll_remove(struct platform_device *pdev)
> > > +{
> > > +     struct gpio_la_poll_priv *priv = platform_get_drvdata(pdev);
> > > +
> > > +     mutex_lock(&priv->lock);
> > > +     debugfs_remove_recursive(priv->debug_dir);
> >
> > ...and this one won't remove it.
> >
> > > +     mutex_unlock(&priv->lock);
> > > +     mutex_destroy(&priv->lock);
> > > +
> > > +     return 0;
> > > +}
> >
> > ...
> >
> > However, I haven't checked if it's pure theoretical issue with the current code
> > base of debugfs or a potential problem. Easy fix is to check an error code and
> 
> I think debugfs_create_dir() can only fail reasonably due to OOM.
> 
> > skip the files creation. Not sure if driver will be useful in that case.
> 
> Having to add such error checks would really be unfortunate, because
> one of the design principles of debugfs is that there is never a need
> to check for errors.

If you really want, you can check the return value of the directory
creation and just return and keep going forward (do NOT propagate an
error upwards as drivers need to keep working if debugfs is hosed).

But really, the only way the call can fail is if you did something wrong
and tried to create a directory that was already there, so don't even
worry about checking the return value, all is fine.

thanks,

greg k-h

On Fri, Jun 02, 2023 at 08:57:36AM +0200, Geert Uytterhoeven wrote:
> On Fri, Jun 2, 2023 at 8:51 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > On Thu, Jun 1, 2023 at 11:40 PM <andy.shevchenko@gmail.com> wrote:
> > > Tue, Mar 29, 2022 at 11:11:26AM +0200, Wolfram Sang kirjoitti:

...

> > > However, I haven't checked if it's pure theoretical issue with the current code
> > > base of debugfs or a potential problem. Easy fix is to check an error code and
> >
> > I think debugfs_create_dir() can only fail reasonably due to OOM.
> 
> Oops, you were talking about NULL, not an error code.
> I don't think that can ever happen.

That's looks correct, I don't see (looking briefly into the fs/debugfs) that
NULL is possible to be returned. Wondering, why the heck we (used to) have
a lot of IS_ERR_OR_NULL() checks.

> And if I did miss something, it would crash when dereferencing a NULL
> pointer in d_really_is_positive() (as called in start_creating())...

I don't see how, but I see a big comment on top of `if (!parent)`.

> Year passed. Any news here?

Well, the issue is that Steven Rostedt told me last years at Kernel
Recipes that disabling the RCU stall detector was bad. He gave me a
pointer where to look for a potentially better solution but I forgot to
note it. When I asked him by mail again for that pointer, he was too
busy to answer and since then I had other things to do. But Steve is at
EOSS end of June as well as me. Asking him again there is big on my
list. Nice you remembered this patch :)