[PATCH v2 2/2] gpio: create the /sys/class/gpio mount point with GPIO_SYSFS disabled

[Bartosz Golaszewski <brgl@bgdev.pl>]

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

User-space may want to use some kind of a compatibility layer for the
deprecated GPIO sysfs ABI. This would typically involve mounting
a fuse-based filesystem using the GPIO character device to emulate the
sysfs behavior and layout.

With GPIO_SYSFS disabled, the /sys/class/gpio directory doesn't exist
and user-space cannot create it. In order to facilitate moving away from
the sysfs, add a new Kconfig option that indicates to GPIOLIB that is
should create an always-empty directory where the GPIO class interface
would exist and enable this option by default if GPIO_SYSFS is not
selected.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
 drivers/gpio/Kconfig   | 18 ++++++++++++++++++
 drivers/gpio/gpiolib.c |  6 ++++++
 2 files changed, 24 insertions(+)

diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index efddc6455315..1a3535bda779 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -69,6 +69,24 @@ config GPIO_SYSFS
 	  use the character device /dev/gpiochipN with the appropriate
 	  ioctl() operations instead.
 
+config GPIO_SYSFS_CLASS_MOUNT_POINT
+	bool "Create empty /sys/class/gpio directory" if EXPERT
+	depends on !GPIO_SYSFS
+	default y
+	help
+	  Say Y here to create an empty /sys/class/gpio directory.
+
+	  User-space may want to use some kind of a compatibility layer for the
+	  deprecated GPIO sysfs ABI. This would typically involve mounting
+	  a fuse-based filesystem using the GPIO character device to emulate
+	  the sysfs behavior and layout.
+
+	  This option makes GPIOLIB create an empty directory at /sys/class/gpio
+	  where user-space can mount the sysfs replacement and avoid having to
+	  change existing programs to adjust to different filesystem paths.
+
+	  If unsure, say Y.
+
 config GPIO_CDEV
 	bool
 	prompt "Character device (/dev/gpiochipN) support" if EXPERT
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 97346b746ef5..1c8bd765d8e1 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -4899,6 +4899,12 @@ static int __init gpiolib_dev_init(void)
 		return ret;
 	}
 
+#if IS_ENABLED(CONFIG_GPIO_SYSFS_CLASS_MOUNT_POINT)
+	ret = sysfs_create_mount_point(class_kobj, "gpio");
+	if (ret)
+		pr_err("gpiolib: failed to create the GPIO class mountpoint\n");
+#endif /* CONFIG_GPIO_SYSFS_CLASS_MOUNT_POINT */
+
 	gpiolib_initialized = true;
 	gpiochip_setup_devs();
 

-- 
2.43.0