linux-kernel - ATTENTION USERS/TESTERS: Re: [PATCH v1] leds: introduce ordered workqueue for leds events instead of system

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Message-ID: <20240822133819.GJ6858@google.com>
Date: Thu, 22 Aug 2024 14:38:19 +0100
From: Lee Jones <lee@...nel.org>
To: Dmitry Rokosov <ddrokosov@...utedevices.com>
Cc: pavel@....cz, linux-kernel@...r.kernel.org, linux-leds@...r.kernel.org,
	kernel@...utedevices.com, rockosov@...il.com,
	Alexey Romanov <avromanov@...utedevices.com>
Subject: ATTENTION USERS/TESTERS: Re: [PATCH v1] leds: introduce ordered
 workqueue for leds events instead of system_wq

INTENTIONAL TOP POST:

This is going to need more time on the list and hopefully draws the
attention of some potentially affected users / to-be testers.

> 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@...utedevices.com>
> Signed-off-by: Dmitry Rokosov <ddrokosov@...utedevices.com>
> ---
>  drivers/leds/led-class.c | 12 +++++++++++-
>  drivers/leds/led-core.c  |  6 +++---
>  include/linux/leds.h     |  1 +
>  3 files changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
> index ba1be15cfd8e..fba12471cf1f 100644
> --- 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 89c9806cc97f..9769ac49be20 100644
> --- a/drivers/leds/led-core.c
> +++ b/drivers/leds/led-core.c
> @@ -266,7 +266,7 @@ 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;
>  	}
>  
> @@ -297,7 +297,7 @@ 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);
> @@ -333,7 +333,7 @@ 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 6300313c46b7..7c9f1cb12ab9 100644
> --- a/include/linux/leds.h
> +++ b/include/linux/leds.h
> @@ -169,6 +169,7 @@ 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;
> -- 
> 2.43.0
> 
> 

-- 
Lee Jones [李琼斯]