[PATCH v2 5/6] gpiolib: switch the line state notifier to atomic

[Bartosz Golaszewski <brgl@xxxxxxxx>]

From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>

With everything else ready, we can now switch to using the atomic
notifier for line state events which will allow us to notify user-space
about direction changes from atomic context.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
---
 drivers/gpio/gpiolib-cdev.c | 22 ++++++++++++++++------
 drivers/gpio/gpiolib.c      |  6 +++---
 drivers/gpio/gpiolib.h      |  2 +-
 3 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index 2677134b52cd..7eae0b17a1d6 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -2673,6 +2673,16 @@ static int lineinfo_changed_notify(struct notifier_block *nb,
 	if (!test_bit(gpio_chip_hwgpio(desc), cdev->watched_lines))
 		return NOTIFY_DONE;
 
+	/*
+	 * This is called from atomic context (with a spinlock taken by the
+	 * atomic notifier chain). Any sleeping calls must be done outside of
+	 * this function in process context of the dedicated workqueue.
+	 *
+	 * Let's gather as much info as possible from the descriptor and
+	 * postpone just the call to pinctrl_gpio_can_use_line() until the work
+	 * is executed.
+	 */
+
 	ctx = kzalloc(sizeof(*ctx), GFP_ATOMIC);
 	if (!ctx) {
 		pr_err("Failed to allocate memory for line info notification\n");
@@ -2837,8 +2847,8 @@ static int gpio_chrdev_open(struct inode *inode, struct file *file)
 	cdev->gdev = gpio_device_get(gdev);
 
 	cdev->lineinfo_changed_nb.notifier_call = lineinfo_changed_notify;
-	ret = blocking_notifier_chain_register(&gdev->line_state_notifier,
-					       &cdev->lineinfo_changed_nb);
+	ret = atomic_notifier_chain_register(&gdev->line_state_notifier,
+					     &cdev->lineinfo_changed_nb);
 	if (ret)
 		goto out_free_bitmap;
 
@@ -2862,8 +2872,8 @@ static int gpio_chrdev_open(struct inode *inode, struct file *file)
 	blocking_notifier_chain_unregister(&gdev->device_notifier,
 					   &cdev->device_unregistered_nb);
 out_unregister_line_notifier:
-	blocking_notifier_chain_unregister(&gdev->line_state_notifier,
-					   &cdev->lineinfo_changed_nb);
+	atomic_notifier_chain_unregister(&gdev->line_state_notifier,
+					 &cdev->lineinfo_changed_nb);
 out_free_bitmap:
 	gpio_device_put(gdev);
 	bitmap_free(cdev->watched_lines);
@@ -2887,8 +2897,8 @@ static int gpio_chrdev_release(struct inode *inode, struct file *file)
 
 	blocking_notifier_chain_unregister(&gdev->device_notifier,
 					   &cdev->device_unregistered_nb);
-	blocking_notifier_chain_unregister(&gdev->line_state_notifier,
-					   &cdev->lineinfo_changed_nb);
+	atomic_notifier_chain_unregister(&gdev->line_state_notifier,
+					 &cdev->lineinfo_changed_nb);
 	bitmap_free(cdev->watched_lines);
 	gpio_device_put(gdev);
 	kfree(cdev);
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 839036b116a2..9b10f47832d5 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1026,7 +1026,7 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 		}
 	}
 
-	BLOCKING_INIT_NOTIFIER_HEAD(&gdev->line_state_notifier);
+	ATOMIC_INIT_NOTIFIER_HEAD(&gdev->line_state_notifier);
 	BLOCKING_INIT_NOTIFIER_HEAD(&gdev->device_notifier);
 
 	ret = init_srcu_struct(&gdev->srcu);
@@ -4089,8 +4089,8 @@ EXPORT_SYMBOL_GPL(gpiod_set_array_value_cansleep);
 
 void gpiod_line_state_notify(struct gpio_desc *desc, unsigned long action)
 {
-	blocking_notifier_call_chain(&desc->gdev->line_state_notifier,
-				     action, desc);
+	atomic_notifier_call_chain(&desc->gdev->line_state_notifier,
+				   action, desc);
 }
 
 /**
diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index d24cd9e8b17c..2799157a1f6b 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -72,7 +72,7 @@ struct gpio_device {
 	const char		*label;
 	void			*data;
 	struct list_head        list;
-	struct blocking_notifier_head line_state_notifier;
+	struct atomic_notifier_head line_state_notifier;
 	struct workqueue_struct	*line_state_wq;
 	struct blocking_notifier_head device_notifier;
 	struct srcu_struct	srcu;

-- 
2.43.0