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

Bartosz Golaszewski
2024-10-10T09:10:41Z

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

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@linaro.org>
---
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