[PATCH RFC/RFT 14/15] gpio: sysfs: allow disabling the legacy parts of the GPIO sysfs interface

[Bartosz Golaszewski <brgl@bgdev.pl>]

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

Add a Kconfig switch allowing to disable the legacy parts of the GPIO
sysfs interface. This means that even though we keep the
/sys/class/gpio/ directory, it no longer contains the global
export/unexport attribute pair (instead, the user should use the
per-chip export/unpexport) nor the gpiochip$BASE entries. This option
default to y if GPIO sysfs is enabled but we'll default it to n at some
point in the future.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
 drivers/gpio/Kconfig         |  8 ++++++++
 drivers/gpio/gpiolib-sysfs.c | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 44f922e10db2f8dcbdacf79ccd27b0fd9cd93564..d040fdd95ee4b19851057fbedbb023f277149c9c 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -69,6 +69,14 @@ config GPIO_SYSFS
 	  use the character device /dev/gpiochipN with the appropriate
 	  ioctl() operations instead.
 
+config GPIO_SYSFS_LEGACY
+	bool "Enable legacy functionalities of the sysfs interface"
+	depends on GPIO_SYSFS
+	default y if GPIO_SYSFS
+	help
+	  Say Y here if you want to enable the legacy, global GPIO
+	  numberspace-based functionalities of the sysfs interface.
+
 config GPIO_CDEV
 	bool "Character device (/dev/gpiochipN) support" if EXPERT
 	default y
diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
index d8c17d71d5458011d15bc4239bd4c041244da3fd..48e1353f966837d46f00b552f870440097ecfe18 100644
--- a/drivers/gpio/gpiolib-sysfs.c
+++ b/drivers/gpio/gpiolib-sysfs.c
@@ -46,7 +46,9 @@ struct gpiod_data {
 	struct device *dev;
 
 	struct mutex mutex;
+#if IS_ENABLED(CONFIG_GPIO_SYSFS_LEGACY)
 	struct kernfs_node *value_class_node;
+#endif /* CONFIG_GPIO_SYSFS_LEGACY */
 	struct kernfs_node *value_chip_node;
 	int irq;
 	unsigned char irq_flags;
@@ -67,7 +69,9 @@ struct gpiod_data {
 
 struct gpiodev_data {
 	struct gpio_device *gdev;
+#if IS_ENABLED(CONFIG_GPIO_SYSFS_LEGACY)
 	struct device *cdev_base; /* Class device by GPIO base */
+#endif /* CONFIG_GPIO_SYSFS_LEGACY */
 	struct device *cdev_id; /* Class device by GPIO device ID */
 	struct list_head exported_lines;
 };
@@ -181,7 +185,9 @@ static irqreturn_t gpio_sysfs_irq(int irq, void *priv)
 {
 	struct gpiod_data *data = priv;
 
+#if IS_ENABLED(CONFIG_GPIO_SYSFS_LEGACY)
 	sysfs_notify_dirent(data->value_class_node);
+#endif /* CONFIG_GPIO_SYSFS_LEGACY */
 	kernfs_notify(data->value_chip_node);
 
 	return IRQ_HANDLED;
@@ -416,6 +422,7 @@ static umode_t gpio_is_visible(struct kobject *kobj, struct attribute *attr,
  *   /ngpio ... matching gpio_chip.ngpio
  */
 
+#if IS_ENABLED(CONFIG_GPIO_SYSFS_LEGACY)
 static ssize_t base_show(struct device *dev, struct device_attribute *attr,
 			 char *buf)
 {
@@ -424,6 +431,7 @@ static ssize_t base_show(struct device *dev, struct device_attribute *attr,
 	return sysfs_emit(buf, "%u\n", data->gdev->base);
 }
 static DEVICE_ATTR_RO(base);
+#endif /* CONFIG_GPIO_SYSFS_LEGACY */
 
 static ssize_t label_show(struct device *dev, struct device_attribute *attr,
 			  char *buf)
@@ -548,6 +556,7 @@ static struct device_attribute dev_attr_unexport = __ATTR(unexport, 0200,
 							  NULL,
 							  chip_unexport_store);
 
+#if IS_ENABLED(CONFIG_GPIO_SYSFS_LEGACY)
 static struct attribute *gpiochip_attrs[] = {
 	&dev_attr_base.attr,
 	&dev_attr_label.attr,
@@ -555,6 +564,7 @@ static struct attribute *gpiochip_attrs[] = {
 	NULL,
 };
 ATTRIBUTE_GROUPS(gpiochip);
+#endif /* CONFIG_GPIO_SYSFS_LEGACY */
 
 static struct attribute *gpiochip_ext_attrs[] = {
 	&dev_attr_label.attr,
@@ -565,6 +575,7 @@ static struct attribute *gpiochip_ext_attrs[] = {
 };
 ATTRIBUTE_GROUPS(gpiochip_ext);
 
+#if IS_ENABLED(CONFIG_GPIO_SYSFS_LEGACY)
 /*
  * /sys/class/gpio/export ... write-only
  *	integer N ... number of GPIO to export (full access)
@@ -629,10 +640,13 @@ static struct attribute *gpio_class_attrs[] = {
 	NULL,
 };
 ATTRIBUTE_GROUPS(gpio_class);
+#endif /* CONFIG_GPIO_SYSFS_LEGACY */
 
 static const struct class gpio_class = {
 	.name =		"gpio",
+#if IS_ENABLED(CONFIG_GPIO_SYSFS_LEGACY)
 	.class_groups =	gpio_class_groups,
+#endif /* CONFIG_GPIO_SYSFS_LEGACY */
 };
 
 static int match_gdev(struct device *dev, const void *desc)
@@ -763,6 +777,7 @@ int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
 	 * at least one known user of gpiod_export_link() in the tree. This
 	 * function still uses class_find_device() internally.
 	 */
+#if IS_ENABLED(CONFIG_GPIO_SYSFS_LEGACY)
 	desc_data->dev = device_create_with_groups(&gpio_class, &gdev->dev,
 						   MKDEV(0, 0), desc_data,
 						   desc_data->attr_groups,
@@ -779,6 +794,7 @@ int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
 		status = -ENODEV;
 		goto err_unregister_device;
 	}
+#endif /* CONFIG_GPIO_SYSFS_LEGACY */
 
 	gdev_data = gdev_get_data(gdev);
 	if (!gdev_data) {
@@ -822,10 +838,12 @@ int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
 err_free_name:
 	kfree(desc_data->attr_group.name);
 err_put_dirent:
+#if IS_ENABLED(CONFIG_GPIO_SYSFS_LEGACY)
 	sysfs_put(desc_data->value_class_node);
 err_unregister_device:
 	device_unregister(desc_data->dev);
 err_free_data:
+#endif /* CONFIG_GPIO_SYSFS_LEGACY */
 	kfree(desc_data);
 err_clear_bit:
 	clear_bit(FLAG_EXPORT, &desc->flags);
@@ -834,12 +852,14 @@ int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
 }
 EXPORT_SYMBOL_GPL(gpiod_export);
 
+#if IS_ENABLED(CONFIG_GPIO_SYSFS_LEGACY)
 static int match_export(struct device *dev, const void *desc)
 {
 	struct gpiod_data *data = dev_get_drvdata(dev);
 
 	return data->desc == desc;
 }
+#endif /* CONFIG_GPIO_SYSFS_LEGACY */
 
 /**
  * gpiod_export_link - create a sysfs link to an exported GPIO node
@@ -856,6 +876,7 @@ static int match_export(struct device *dev, const void *desc)
 int gpiod_export_link(struct device *dev, const char *name,
 		      struct gpio_desc *desc)
 {
+#if IS_ENABLED(CONFIG_GPIO_SYSFS_LEGACY)
 	struct device *cdev;
 	int ret;
 
@@ -872,6 +893,9 @@ int gpiod_export_link(struct device *dev, const char *name,
 	put_device(cdev);
 
 	return ret;
+#else
+	return -EOPNOTSUPP;
+#endif /* CONFIG_GPIO_SYSFS_LEGACY */
 }
 EXPORT_SYMBOL_GPL(gpiod_export_link);
 
@@ -910,8 +934,10 @@ void gpiod_unexport(struct gpio_desc *desc)
 
 		list_del(&desc_data->list);
 		clear_bit(FLAG_EXPORT, &desc->flags);
+#if IS_ENABLED(CONFIG_GPIO_SYSFS_LEGACY)
 		sysfs_put(desc_data->value_class_node);
 		device_unregister(desc_data->dev);
+#endif /* CONFIG_GPIO_SYSFS_LEGACY */
 		kernfs_put(desc_data->value_chip_node);
 
 		/*
@@ -966,6 +992,7 @@ int gpiochip_sysfs_register(struct gpio_device *gdev)
 
 	guard(mutex)(&sysfs_lock);
 
+#if IS_ENABLED(CONFIG_GPIO_SYSFS_LEGACY)
 	/* use chip->base for the ID; it's already known to be unique */
 	data->cdev_base = device_create_with_groups(&gpio_class, parent,
 						    MKDEV(0, 0), data,
@@ -976,13 +1003,16 @@ int gpiochip_sysfs_register(struct gpio_device *gdev)
 		kfree(data);
 		return PTR_ERR(data->cdev_base);
 	}
+#endif /* CONFIG_GPIO_SYSFS_LEGACY */
 
 	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)) {
+#if IS_ENABLED(CONFIG_GPIO_SYSFS_LEGACY)
 		device_unregister(data->cdev_base);
+#endif /* CONFIG_GPIO_SYSFS_LEGACY */
 		kfree(data);
 		return PTR_ERR(data->cdev_id);
 	}
@@ -1001,7 +1031,9 @@ void gpiochip_sysfs_unregister(struct gpio_device *gdev)
 		if (!data)
 			return;
 
+#if IS_ENABLED(CONFIG_GPIO_SYSFS_LEGACY)
 		device_unregister(data->cdev_base);
+#endif /* CONFIG_GPIO_SYSFS_LEGACY */
 		device_unregister(data->cdev_id);
 		kfree(data);
 	}

-- 
2.48.1