Commit 2028f854 authored by Bartosz Golaszewski's avatar Bartosz Golaszewski
Browse files

gpio: sysfs: add a parallel class device for each GPIO chip using device IDs 



In order to enable moving away from the global GPIO numberspace-based
exporting of lines over sysfs: add a parallel, per-chip entry under
/sys/class/gpio/ for every registered GPIO chip, denoted by device ID
in the file name and not its base GPIO number.

Compared to the existing chip group: it does not contain the "base"
attribute as the goal of this change is to not refer to GPIOs by their
global number from user-space anymore. It also contains its own,
per-chip export/unexport attribute pair which allow to export lines by
their hardware offset within the chip.

Caveat #1: the new device cannot be a link to (or be linked to by) the
existing "gpiochip<BASE>" entry as we cannot create links in
/sys/class/xyz/.

Caveat #2: the new entry cannot be named "gpiochipX" as it could
conflict with devices whose base is statically defined to a low number.
Let's go with "chipX" instead.

While at it: the chip label is unique so update the untrue statement
when extending the docs.

Acked-by: default avatarLinus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20250704-gpio-sysfs-chip-export-v4-2-9289d8758243@linaro.org


Signed-off-by: default avatarBartosz Golaszewski <bartosz.golaszewski@linaro.org>
parent 32ad0b9a

Documentation/ABI/obsolete/sysfs-gpio

+6 −1
Original line number Diff line number Diff line
@@ -25,8 +25,13 @@ Description: 
	    /active_low ... r/w as: 0, 1

	/gpiochipN ... for each gpiochip; #N is its first GPIO

	    /base ... (r/o) same as N

	    /label ... (r/o) descriptive, not necessarily unique

	    /label ... (r/o) descriptive chip name

	    /ngpio ... (r/o) number of GPIOs; numbered N to N + (ngpio - 1)

	/chipX ... for each gpiochip; #X is the gpio device ID

	    /export ... asks the kernel to export a GPIO at HW offset X to userspace

	    /unexport ... to return a GPIO at HW offset X to the kernel

	    /label ... (r/o) descriptive chip name

	    /ngpio ... (r/o) number of GPIOs exposed by the chip



  This ABI is obsoleted by Documentation/ABI/testing/gpio-cdev and will be

  removed after 2020.

drivers/gpio/gpiolib-sysfs.c

+144 −48
Original line number Diff line number Diff line
@@ -45,6 +45,7 @@ struct gpiod_data { 


struct gpiodev_data {

	struct gpio_device *gdev;

	struct device *cdev_id; /* Class device by GPIO device ID */

	struct device *cdev_base; /* Class device by GPIO base */

};
@@ -399,6 +400,14 @@ static const struct attribute_group *gpio_groups[] = { 
 *   /base ... matching gpio_chip.base (N)

 *   /label ... matching gpio_chip.label

 *   /ngpio ... matching gpio_chip.ngpio

 *

 * AND

 *

 * /sys/class/gpio/chipX/

 *   /export ... export GPIO at given offset

 *   /unexport ... unexport GPIO at given offset

 *   /label ... matching gpio_chip.label

 *   /ngpio ... matching gpio_chip.ngpio

 */



static ssize_t base_show(struct device *dev, struct device_attribute *attr,
@@ -428,6 +437,111 @@ static ssize_t ngpio_show(struct device *dev, struct device_attribute *attr, 
}

static DEVICE_ATTR_RO(ngpio);



static int export_gpio_desc(struct gpio_desc *desc)

{

	int offset, ret;



	CLASS(gpio_chip_guard, guard)(desc);

	if (!guard.gc)

		return -ENODEV;



	offset = gpio_chip_hwgpio(desc);

	if (!gpiochip_line_is_valid(guard.gc, offset)) {

		pr_debug_ratelimited("%s: GPIO %d masked\n", __func__,

				     gpio_chip_hwgpio(desc));

		return -EINVAL;

	}



	/*

	 * No extra locking here; FLAG_SYSFS just signifies that the

	 * request and export were done by on behalf of userspace, so

	 * they may be undone on its behalf too.

	 */



	ret = gpiod_request_user(desc, "sysfs");

	if (ret)

		return ret;



	ret = gpiod_set_transitory(desc, false);

	if (ret) {

		gpiod_free(desc);

		return ret;

	}



	ret = gpiod_export(desc, true);

	if (ret < 0) {

		gpiod_free(desc);

	} else {

		set_bit(FLAG_SYSFS, &desc->flags);

		gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_REQUESTED);

	}



	return ret;

}



static int unexport_gpio_desc(struct gpio_desc *desc)

{

	/*

	 * No extra locking here; FLAG_SYSFS just signifies that the

	 * request and export were done by on behalf of userspace, so

	 * they may be undone on its behalf too.

	 */

	if (!test_and_clear_bit(FLAG_SYSFS, &desc->flags))

		return -EINVAL;



	gpiod_unexport(desc);

	gpiod_free(desc);



	return 0;

}



static ssize_t do_chip_export_store(struct device *dev,

				    struct device_attribute *attr,

				    const char *buf, ssize_t size,

				    int (*handler)(struct gpio_desc *desc))

{

	struct gpiodev_data *data = dev_get_drvdata(dev);

	struct gpio_device *gdev = data->gdev;

	struct gpio_desc *desc;

	unsigned int gpio;

	int ret;



	ret = kstrtouint(buf, 0, &gpio);

	if (ret)

		return ret;



	desc = gpio_device_get_desc(gdev, gpio);

	if (IS_ERR(desc))

		return PTR_ERR(desc);



	ret = handler(desc);

	if (ret)

		return ret;



	return size;

}



static ssize_t chip_export_store(struct device *dev,

				 struct device_attribute *attr,

				 const char *buf, size_t size)

{

	return do_chip_export_store(dev, attr, buf, size, export_gpio_desc);

}



static struct device_attribute dev_attr_export = __ATTR(export, 0200, NULL,

							chip_export_store);



static ssize_t chip_unexport_store(struct device *dev,

				   struct device_attribute *attr,

				   const char *buf, size_t size)

{

	return do_chip_export_store(dev, attr, buf, size, unexport_gpio_desc);

}



static struct device_attribute dev_attr_unexport = __ATTR(unexport, 0200,

							  NULL,

							  chip_unexport_store);



static struct attribute *gpiochip_attrs[] = {

	&dev_attr_base.attr,

	&dev_attr_label.attr,
@@ -436,6 +550,15 @@ static struct attribute *gpiochip_attrs[] = { 
};

ATTRIBUTE_GROUPS(gpiochip);



static struct attribute *gpiochip_ext_attrs[] = {

	&dev_attr_label.attr,

	&dev_attr_ngpio.attr,

	&dev_attr_export.attr,

	&dev_attr_unexport.attr,

	NULL

};

ATTRIBUTE_GROUPS(gpiochip_ext);



/*

 * /sys/class/gpio/export ... write-only

 *	integer N ... number of GPIO to export (full access)
@@ -447,7 +570,7 @@ static ssize_t export_store(const struct class *class, 
			    const char *buf, size_t len)

{

	struct gpio_desc *desc;

	int status, offset;

	int status;

	long gpio;



	status = kstrtol(buf, 0, &gpio);
@@ -461,40 +584,7 @@ static ssize_t export_store(const struct class *class, 
		return -EINVAL;

	}



	CLASS(gpio_chip_guard, guard)(desc);

	if (!guard.gc)

		return -ENODEV;



	offset = gpio_chip_hwgpio(desc);

	if (!gpiochip_line_is_valid(guard.gc, offset)) {

		pr_debug_ratelimited("%s: GPIO %ld masked\n", __func__, gpio);

		return -EINVAL;

	}



	/* No extra locking here; FLAG_SYSFS just signifies that the

	 * request and export were done by on behalf of userspace, so

	 * they may be undone on its behalf too.

	 */



	status = gpiod_request_user(desc, "sysfs");

	if (status)

		goto done;



	status = gpiod_set_transitory(desc, false);

	if (status) {

		gpiod_free(desc);

		goto done;

	}



	status = gpiod_export(desc, true);

	if (status < 0) {

		gpiod_free(desc);

	} else {

		set_bit(FLAG_SYSFS, &desc->flags);

		gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_REQUESTED);

	}



done:

	status = export_gpio_desc(desc);

	if (status)

		pr_debug("%s: status %d\n", __func__, status);

	return status ? : len;
@@ -511,7 +601,7 @@ static ssize_t unexport_store(const struct class *class, 


	status = kstrtol(buf, 0, &gpio);

	if (status < 0)

		goto done;

		return status;



	desc = gpio_to_desc(gpio);

	/* reject bogus commands (gpiod_unexport() ignores them) */
@@ -520,18 +610,7 @@ static ssize_t unexport_store(const struct class *class, 
		return -EINVAL;

	}



	status = -EINVAL;



	/* No extra locking here; FLAG_SYSFS just signifies that the

	 * request and export were done by on behalf of userspace, so

	 * they may be undone on its behalf too.

	 */

	if (test_and_clear_bit(FLAG_SYSFS, &desc->flags)) {

		gpiod_unexport(desc);

		gpiod_free(desc);

		status = 0;

	}

done:

	status = unexport_gpio_desc(desc);

	if (status)

		pr_debug("%s: status %d\n", __func__, status);

	return status ? : len;
@@ -561,6 +640,11 @@ static int match_gdev(struct device *dev, const void *desc) 
static struct gpiodev_data *

gdev_get_data(struct gpio_device *gdev) __must_hold(&sysfs_lock)

{

	/*

	 * Find the first device in GPIO class that matches. Whether that's

	 * the one indexed by GPIO base or device ID doesn't matter, it has

	 * the same address set as driver data.

	 */

	struct device *cdev __free(put_device) = class_find_device(&gpio_class,

								   NULL, gdev,

								   match_gdev);
@@ -787,6 +871,17 @@ int gpiochip_sysfs_register(struct gpio_device *gdev) 
		return err;

	}



	data->cdev_id = device_create_with_groups(&gpio_class, parent,

						  MKDEV(0, 0), data,

						  gpiochip_ext_groups,

						  "chip%d", gdev->id);

	if (IS_ERR(data->cdev_id)) {

		device_unregister(data->cdev_base);

		err = PTR_ERR(data->cdev_id);

		kfree(data);

		return err;

	}



	return 0;

}
@@ -802,6 +897,7 @@ void gpiochip_sysfs_unregister(struct gpio_device *gdev) 
			return;



		device_unregister(data->cdev_base);

		device_unregister(data->cdev_id);

		kfree(data);

	}