Hi Wolfram,
On Sat, Sep 18, 2021 at 4:22 PM Wolfram Sang
<wsa+renesas@xxxxxxxxxxxxxxxxxxxx> 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.
>
> Signed-off-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
Thanks for your patch!
Note that this is the second posting using v2, and the previous version
was simultaneously v1 and v3 (branch renesas/gpio-logic-analyzer-v3).
Resetting version numbers may confuse people and tools (e.g. b4).
> --- /dev/null
> +++ b/Documentation/dev-tools/gpio-sloppy-logic-analyzer.rst
> @@ -0,0 +1,71 @@
> +=============================================
> +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.
> +
> +Note that this is a last resort analyzer which can be affected by latencies,
> +non-determinant code paths and non-maskable interrupts. It is called 'sloppy'
non-deterministic?
> +for a reason. However, for e.g. remote development, it may be useful to get a
> +first view and aid further debugging.
> +
> +Setup
> +=====
> +
> +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 least disturbance
the least
> +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
kHz
> +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/
> --- a/drivers/gpio/Kconfig
> +++ b/drivers/gpio/Kconfig
> @@ -1682,4 +1682,21 @@ config GPIO_VIRTIO
>
> endmenu
>
> +menu "GPIO hardware hacking tools"
> +
> +config GPIO_LOGIC_ANALYZER
> + tristate "Sloppy GPIO logic analyzer"
> + depends on (GPIOLIB || COMPILE_TEST) && 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 using it easier and will also
make it easier to use?
> + isolate a CPU for the polling task. Note that this is a last resort
> + analyzer which can be affected by latencies, non-determinant code
deterministic
> + 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
> --- /dev/null
> +++ b/drivers/gpio/gpio-sloppy-logic-analyzer.c
> @@ -0,0 +1,341 @@
> +// 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-determinant code paths.
deterministic
> + * However, for e.g. remote development, it may be useful to get a first view
> + * and aid further debugging.
> +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;
> + int i, ret;
unsigned int i
> +
> + 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 gpio_err;
> + }
> +
> + priv->acq_delay = ktime_sub(ktime_get(), start_time) / GPIO_LA_NUM_TESTS;
> + if (priv->delay_ns < priv->acq_delay) {
> + ret = -ERANGE;
> + goto gpio_err;
> + }
> +
> + 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 gpio_err;
> +
> + 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 gpio_err;
> +
> + la_buf[priv->buf_idx++] = state;
> + ndelay(delay);
> + }
> +gpio_err:
> + 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;
> +}
> +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 meta_len = 0;
> + int ret, i;
unsigned int i;
> +
> + 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 = -ENODATA;
> + if (ret < 0) {
> + dev_err(dev, "error naming the GPIOs: %d\n", ret);
> + return ret;
> + }
> +
> + 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%02d=%s\n",
%02u
> + i + 1, gpio_names[i]);
> + }
> --- /dev/null
> +++ b/tools/gpio/gpio-sloppy-logic-analyzer
> @@ -0,0 +1,221 @@
> +#!/bin/sh -eu
> +# Helper script for the Linux Kernel GPIO sloppy logic analyzer
> +#
> +# Copyright (C) Wolfram Sang <wsa@xxxxxxxxxxxxxxxxxxxx>
> +# Copyright (C) Renesas Electronics Corporation
> +#
> +# TODO: support SI units in command line parameters?
> +
> +samplefreq=1000000
> +numsamples=250000
> +cpusetdir='/dev/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
> +$progname - helper script for the Linux Kernel Sloppy GPIO Logic Analyzer
> +Available options:
> + -c|--cpu <n>: which CPU to isolate for sampling. Only needed once. Default <1>.
> + Remember that a more powerful CPU gives you higher sample speeds.
sampling speeds
> + Also CPU0 is not recommended as it usually does extra bookkeeping.
> + -d|--duration-us <n>: number of microseconds to sample. Overrides -n, no default value.
> + -h|--help: print this help
> + -i|--instance <str>: name of the logic analyzer in case you have multiple instances. Default
> + to first instance found
> + -k|--kernel-debug-dir: path to the kernel debugfs mountpoint. Default: <$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 sample frequency. Might be capped if too large. Default: 1MHz.
sampling
> + -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:
µs
> + '$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
> +}
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
