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

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Message-Id: <75B39716-5795-4F19-BC74-A4C21F99B85E@canonical.com>
Date:   Thu, 2 Jul 2020 13:20:21 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc:     pavel@....cz, 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



> On Jul 2, 2020, at 05:28, Jacek Anaszewski <jacek.anaszewski@...il.com> wrote:
> 
> 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?

Yes, mute and micmute LED on laptops sometimes are still on during suspend-to-idle.

> 
>> 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.

Right, will send v2.

Kai-Heng

> 
> -- 
> Best regards,
> Jacek Anaszewski