leds: Introduce ordered workqueue for LEDs events instead of system_wq

This allows to setup ordered workqueue for LEDs events. This may be
useful, because default 'system_wq' does not guarantee execution order
of each work_struct, thus for several brightness update requests (for
multiple LEDs), real brightness switch could be in random order.

Yes, for sysfs-based LEDs we have flush_work() call inside
brightness_store() operation, but it's blocking call, so userspace
caller can be blocked at a long time, which means LEDs animation stream
can be broken.

Ordered workqueue has the same behaviour as system_wq + flush_work(),
but all scheduled works are async and userspace caller is not blocked,
which it better for userspace animation scheduling.

Signed-off-by: Alexey Romanov <avromanov@salutedevices.com>
Signed-off-by: Dmitry Rokosov <ddrokosov@salutedevices.com>
Link: https://lore.kernel.org/r/20240903223936.21292-1-ddrokosov@salutedevices.com
[Lee: Couple of style fix-ups]
Signed-off-by: Lee Jones <lee@kernel.org>

diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index 06b97fd..83e512d 100644 (file)
--- a/drivers/leds/led-class.c
+++ b/drivers/leds/led-class.c
@@ -25,6 +25,8 @@
 static DEFINE_MUTEX(leds_lookup_lock);
 static LIST_HEAD(leds_lookup_list);
 
+static struct workqueue_struct *leds_wq;
+
 static ssize_t brightness_show(struct device *dev,
                struct device_attribute *attr, char *buf)
 {
@@ -57,7 +59,6 @@ static ssize_t brightness_store(struct device *dev,
        if (state == LED_OFF)
                led_trigger_remove(led_cdev);
        led_set_brightness(led_cdev, state);
-       flush_work(&led_cdev->set_brightness_work);
 
        ret = size;
 unlock:
@@ -549,6 +550,8 @@ int led_classdev_register_ext(struct device *parent,
 
        led_update_brightness(led_cdev);
 
+       led_cdev->wq = leds_wq;
+
        led_init_core(led_cdev);
 
 #ifdef CONFIG_LEDS_TRIGGERS
@@ -667,12 +670,19 @@ EXPORT_SYMBOL_GPL(devm_led_classdev_unregister);
 
 static int __init leds_init(void)
 {
+       leds_wq = alloc_ordered_workqueue("leds", 0);
+       if (!leds_wq) {
+               pr_err("Failed to create LEDs ordered workqueue\n");
+               return -ENOMEM;
+       }
+
        return class_register(&leds_class);
 }
 
 static void __exit leds_exit(void)
 {
        class_unregister(&leds_class);
+       destroy_workqueue(leds_wq);
 }
 
 subsys_initcall(leds_init);

diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
index 001c290..f6c46d2 100644 (file)
--- a/drivers/leds/led-core.c
+++ b/drivers/leds/led-core.c
@@ -273,7 +273,7 @@ void led_blink_set_nosleep(struct led_classdev *led_cdev, unsigned long delay_on
                led_cdev->delayed_delay_on = delay_on;
                led_cdev->delayed_delay_off = delay_off;
                set_bit(LED_SET_BLINK, &led_cdev->work_flags);
-               schedule_work(&led_cdev->set_brightness_work);
+               queue_work(led_cdev->wq, &led_cdev->set_brightness_work);
                return;
        }
 
@@ -304,7 +304,7 @@ void led_set_brightness(struct led_classdev *led_cdev, unsigned int brightness)
                 */
                if (!brightness) {
                        set_bit(LED_BLINK_DISABLE, &led_cdev->work_flags);
-                       schedule_work(&led_cdev->set_brightness_work);
+                       queue_work(led_cdev->wq, &led_cdev->set_brightness_work);
                } else {
                        set_bit(LED_BLINK_BRIGHTNESS_CHANGE,
                                &led_cdev->work_flags);
@@ -340,7 +340,7 @@ void led_set_brightness_nopm(struct led_classdev *led_cdev, unsigned int value)
                set_bit(LED_SET_BRIGHTNESS_OFF, &led_cdev->work_flags);
        }
 
-       schedule_work(&led_cdev->set_brightness_work);
+       queue_work(led_cdev->wq, &led_cdev->set_brightness_work);
 }
 EXPORT_SYMBOL_GPL(led_set_brightness_nopm);
 

diff --git a/include/linux/leds.h b/include/linux/leds.h
index e5968c3..9f34b9f 100644 (file)
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -171,6 +171,7 @@ struct led_classdev {
        int                      new_blink_brightness;
        void                    (*flash_resume)(struct led_classdev *led_cdev);
 
+       struct workqueue_struct *wq;                    /* LED workqueue */
        struct work_struct      set_brightness_work;
        int                     delayed_set_value;
        unsigned long           delayed_delay_on;