linux-kernel - Re: [PATCH] leds: core: Use blocking op for system suspend

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Message-ID: <38622f5a-4518-cdb4-d1ca-581f470ce797@gmail.com>
Date:   Wed, 1 Jul 2020 23:28:29 +0200
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>, pavel@....cz
Cc:     anthony.wong@...onical.com, Dan Murphy <dmurphy@...com>,
        "open list:LED SUBSYSTEM" <linux-leds@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] leds: core: Use blocking op for system suspend

Hi Kai-Heng,

Thank you for the patch.

On 7/1/20 11:35 AM, Kai-Heng Feng wrote:
> Sometimes LED won't be turned off by LED_CORE_SUSPENDRESUME flag upon
> system suspend.

Just out of curiosity - are you experiencing that on some hardware?

> led_set_brightness_nopm() uses schedule_work() to set LED brightness.
> However, there's no guarantee that the scheduled work gets executed
> because no one calls flush_scheduled_work().
> 
> As flush_scheduled_work() may affect other drivers' suspend routines,
> take a more contained approach which uses blocking op to make sure the
> LED gets turned off.
> 
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> ---
>   drivers/leds/led-core.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
> index f1f718dbe0f8..9a5bfcd7a704 100644
> --- a/drivers/leds/led-core.c
> +++ b/drivers/leds/led-core.c
> @@ -269,6 +269,11 @@ EXPORT_SYMBOL_GPL(led_set_brightness);
>   void led_set_brightness_nopm(struct led_classdev *led_cdev,
>   			      enum led_brightness value)
>   {
> +
> +	if (led_cdev->flags & LED_SUSPENDED &&
> +	    !__led_set_brightness_blocking(led_cdev, value))
> +		return;
> +

This function is "nopm" for a reason - we do not make here any
pm management related operations.

Instead of that, please just add

flush_work(&led_cdev->set_brightness_work);

at the end of led_classdev_suspend()

in drivers/leds/led-class.c.

-- 
Best regards,
Jacek Anaszewski