linux-kernel - [PATCH v4 08/10] gpio: sysfs: export the GPIO directory locally in the gpiochip<id> directory

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Message-Id: <20250704-gpio-sysfs-chip-export-v4-8-9289d8758243@linaro.org>
Date: Fri, 04 Jul 2025 14:58:55 +0200
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Ahmad Fatoum <a.fatoum@...gutronix.de>, 
 Kent Gibson <warthog618@...il.com>, 
 Jan Lübbe <jlu@...gutronix.de>, 
 Marek Vasut <marex@...x.de>, Geert Uytterhoeven <geert+renesas@...der.be>, 
 Linus Walleij <linus.walleij@...aro.org>, 
 Andy Shevchenko <andriy.shevchenko@...el.com>, 
 Bartosz Golaszewski <brgl@...ev.pl>
Cc: linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: [PATCH v4 08/10] gpio: sysfs: export the GPIO directory locally in
 the gpiochip<id> directory

From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>

As a way to allow the user-space to stop referring to GPIOs by their
global numbers, introduce a parallel group of line attributes for
exported GPIO that live inside the GPIO chip class device and are
referred to by their HW offset within their parent chip.

Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
---
 Documentation/ABI/obsolete/sysfs-gpio |  3 +++
 drivers/gpio/gpiolib-sysfs.c          | 51 ++++++++++++++++++++++++++++++++++-
 2 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/obsolete/sysfs-gpio b/Documentation/ABI/obsolete/sysfs-gpio
index ff694708a3bef787afa42dedf94faf209c44dbf0..0d3f12c4dcbde4f93da33707cd36e9acc0ee2fbf 100644
--- a/Documentation/ABI/obsolete/sysfs-gpio
+++ b/Documentation/ABI/obsolete/sysfs-gpio
@@ -27,6 +27,9 @@ Description:
 	    /base ... (r/o) same as N
 	    /label ... (r/o) descriptive chip name
 	    /ngpio ... (r/o) number of GPIOs; numbered N to N + (ngpio - 1)
+	    /gpio<OFFSET>
+	        /value ... always readable, writes fail for input GPIOs
+	        /direction ... r/w as: in, out (default low); write: high, low
 	/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
diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
index ccc293a4cc5d51294703959317061af55fb0dab0..563e38456c33cd3a6e8674485105ef45ce8f5095 100644
--- a/drivers/gpio/gpiolib-sysfs.c
+++ b/drivers/gpio/gpiolib-sysfs.c
@@ -41,6 +41,13 @@ enum {
 	GPIO_SYSFS_LINE_CLASS_ATTR_SIZE,
 };
 
+enum {
+	GPIO_SYSFS_LINE_CHIP_ATTR_DIRECTION = 0,
+	GPIO_SYSFS_LINE_CHIP_ATTR_VALUE,
+	GPIO_SYSFS_LINE_CHIP_ATTR_SENTINEL,
+	GPIO_SYSFS_LINE_CHIP_ATTR_SIZE,
+};
+
 struct gpiod_data {
 	struct list_head list;
 
@@ -54,6 +61,7 @@ struct gpiod_data {
 
 	bool direction_can_change;
 
+	struct kobject *parent;
 	struct device_attribute dir_attr;
 	struct device_attribute val_attr;
 	struct device_attribute edge_attr;
@@ -62,6 +70,10 @@ struct gpiod_data {
 	struct attribute *class_attrs[GPIO_SYSFS_LINE_CLASS_ATTR_SIZE];
 	struct attribute_group class_attr_group;
 	const struct attribute_group *class_attr_groups[2];
+
+	struct attribute *chip_attrs[GPIO_SYSFS_LINE_CHIP_ATTR_SIZE];
+	struct attribute_group chip_attr_group;
+	const struct attribute_group *chip_attr_groups[2];
 };
 
 struct gpiodev_data {
@@ -691,6 +703,7 @@ static void gpiod_attr_init(struct device_attribute *dev_attr, const char *name,
  */
 int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
 {
+	char *path __free(kfree) = NULL;
 	struct gpiodev_data *gdev_data;
 	struct gpiod_data *desc_data;
 	struct gpio_device *gdev;
@@ -780,13 +793,46 @@ int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
 	gdev_data = gdev_get_data(gdev);
 	if (!gdev_data) {
 		status = -ENODEV;
-		goto err_unregister_device;
+		goto err_put_dirent;
+	}
+
+	desc_data->chip_attr_group.name = kasprintf(GFP_KERNEL, "gpio%u",
+						    gpio_chip_hwgpio(desc));
+	if (!desc_data->chip_attr_group.name) {
+		status = -ENOMEM;
+		goto err_put_dirent;
+	}
+
+	attrs = desc_data->chip_attrs;
+	desc_data->chip_attr_group.is_visible = gpio_is_visible;
+	attrs[GPIO_SYSFS_LINE_CHIP_ATTR_DIRECTION] = &desc_data->dir_attr.attr;
+	attrs[GPIO_SYSFS_LINE_CHIP_ATTR_VALUE] = &desc_data->val_attr.attr;
+
+	desc_data->chip_attr_group.attrs = attrs;
+	desc_data->chip_attr_groups[0] = &desc_data->chip_attr_group;
+
+	desc_data->parent = &gdev_data->cdev_id->kobj;
+	status = sysfs_create_groups(desc_data->parent,
+				     desc_data->chip_attr_groups);
+	if (status)
+		goto err_free_name;
+
+	path = kasprintf(GFP_KERNEL, "gpio%u/value", gpio_chip_hwgpio(desc));
+	if (!path) {
+		status = -ENOMEM;
+		goto err_remove_groups;
 	}
 
 	list_add(&desc_data->list, &gdev_data->exported_lines);
 
 	return 0;
 
+err_remove_groups:
+	sysfs_remove_groups(desc_data->parent, desc_data->chip_attr_groups);
+err_free_name:
+	kfree(desc_data->chip_attr_group.name);
+err_put_dirent:
+	sysfs_put(desc_data->value_kn);
 err_unregister_device:
 	device_unregister(desc_data->dev);
 err_free_data:
@@ -883,6 +929,9 @@ void gpiod_unexport(struct gpio_desc *desc)
 		 */
 		if (desc_data->irq_flags)
 			gpio_sysfs_free_irq(desc_data);
+
+		sysfs_remove_groups(desc_data->parent,
+				    desc_data->chip_attr_groups);
 	}
 
 	mutex_destroy(&desc_data->mutex);

-- 
2.48.1