linux-kernel - Re: [PATCH AUTOSEL for 4.9 28/52] led: core: Fix brightness setting when setting delay

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Date:   Sat, 3 Feb 2018 23:34:23 +0100
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Sasha Levin <Alexander.Levin@...rosoft.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Cc:     Matthieu CASTET <matthieu.castet@...rot.com>,
        "linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>
Subject: Re: [PATCH AUTOSEL for 4.9 28/52] led: core: Fix brightness setting
 when setting delay_off=0

On 02/03/2018 10:22 PM, Jacek Anaszewski wrote:
> Hi Sasha,
> 
> All 3.18, 4.4 and 4.9 also require the follow-up
> patch [0], similarly like autosel did it for 4.14,
> since this one alone breaks the other use case.

Actually after taking closer look, it turns out that
the patch [0] applies cleanly only to 4.14.

4.9 requires also the patch :

eb1610b4c273 ("led: core: Fix blink_brightness setting race")

3.18 and 4.4 shouldn't have the issue since it was introduced
along with LED_BLINK_SW flag added in 4.7.

Thanks,
Jacek Anaszewski

> [0] https://lkml.org/lkml/2018/2/3/249
> 
> On 02/03/2018 07:03 PM, Sasha Levin wrote:
>> From: Matthieu CASTET <matthieu.castet@...rot.com>
>>
>> [ Upstream commit 2b83ff96f51d0b039c4561b9f95c824d7bddb85c ]
>>
>> With the current code, the following sequence won't work :
>> echo timer > trigger
>>
>> echo 0 >  delay_off
>> * at this point we call
>> ** led_delay_off_store
>> ** led_blink_set
>> *** stop timer
>> ** led_blink_setup
>> ** led_set_software_blink
>> *** if !delay_on, led off
>> *** if !delay_off, set led_set_brightness_nosleep <--- LED_BLINK_SW is set but timer is stop
>> *** otherwise start timer/set LED_BLINK_SW flag
>>
>> echo xxx > brightness
>> * led_set_brightness
>> ** if LED_BLINK_SW
>> *** if brightness=0, led off
>> *** else apply brightness if next timer <--- timer is stop, and will never apply new setting
>> ** otherwise set led_set_brightness_nosleep
>>
>> To fix that, when we delete the timer, we should clear LED_BLINK_SW.
>>
>> Cc: linux-leds@...r.kernel.org
>> Signed-off-by: Matthieu CASTET <matthieu.castet@...rot.com>
>> Signed-off-by: Jacek Anaszewski <jacek.anaszewski@...il.com>
>> Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
>> ---
>>  drivers/leds/led-core.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
>> index 3bce44893021..d70d4a5273b8 100644
>> --- a/drivers/leds/led-core.c
>> +++ b/drivers/leds/led-core.c
>> @@ -186,7 +186,7 @@ void led_blink_set(struct led_classdev *led_cdev,
>>  		   unsigned long *delay_on,
>>  		   unsigned long *delay_off)
>>  {
>> -	del_timer_sync(&led_cdev->blink_timer);
>> +	led_stop_software_blink(led_cdev);
>>  
>>  	led_cdev->flags &= ~LED_BLINK_ONESHOT;
>>  	led_cdev->flags &= ~LED_BLINK_ONESHOT_STOP;
>>
>