Re: [PATCH v9 1/1] gpio: add sloppy logic analyzer using polling

[Andy Shevchenko <andy.shevchenko@gmail.com>]

Mon, Jun 10, 2024 at 01:26:59PM +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.

...

> +#include <linux/ctype.h>
> +#include <linux/debugfs.h>
> +#include <linux/delay.h>

+ device.h
+ err.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>

+ types.h

> +#include <linux/vmalloc.h>

...

> +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->blob_lock);

guard() (from cleanup.h)?

> +	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->blob_lock);
> +
> +	return ret;
> +}

...

> +static const struct file_operations fops_trigger = {
> +	.owner = THIS_MODULE,
> +	.open = trigger_open,
> +	.write = trigger_write,
> +	.llseek = no_llseek,
> +	.release = single_release,
> +};

Wondering if you can use DEFINE_SHOW_STORE_ATTRIBUTE(), or if it makes sense.
It might be that it requires to use DEFINE_SHOW_ATTRIBUTE() for the sake of
consistency, but I don't remember if there is a difference WRT debugfs usage.

...

> +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->blob_lock);

devm_mutex_init()

> +	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);

Can it be rewritten to use devm_krealloc_array()?

> +		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");

Do we need this? Existence of folder in debugfs is enough indication of
success, no?

> +	return 0;
> +}

...

> +static const struct of_device_id gpio_la_poll_of_match[] = {
> +	{ .compatible = GPIO_LA_NAME, },

Redundant inner comma.

> +	{ }
> +};

...

> +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);

Why? Can we add a comment?

...

Btw, have you tried `shellcheck` against your script?

-- 
With Best Regards,
Andy Shevchenko