linux-kernel - Re: [PATCH v2] leds: fix brightness changing when software blinking is active

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Date:	Wed, 24 Jun 2015 11:53:54 +0200
From:	Jacek Anaszewski <j.anaszewski@...sung.com>
To:	Pavel Machek <pavel@....cz>
Cc:	Stas Sergeev <stsp@...t.ru>, linux-leds@...r.kernel.org,
	Linux kernel <linux-kernel@...r.kernel.org>,
	Bryan Wu <cooloney@...il.com>,
	Richard Purdie <rpurdie@...ys.net>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Stas Sergeev <stsp@...rs.sourceforge.net>
Subject: Re: [PATCH v2] leds: fix brightness changing when software blinking is
 active

On 06/24/2015 10:44 AM, Pavel Machek wrote:
> On Tue 2015-06-23 19:59:27, Stas Sergeev wrote:
>> 02.05.2015 17:59, Pavel Machek пишет:
>>> On Thu 2015-05-14 18:24:02, Stas Sergeev wrote:
>>>>
>>>> The following sequence:
>>>> echo timer >/sys/class/leds/<name>/trigger
>>>> echo 1 >/sys/class/leds/<name>/brightness
>>>> should change the ON brightness for blinking.
>>>> The function led_set_brightness() was mistakenly initiating the
>>>> delayed blink stop procedure, which resulted in no blinking with
>>>> the timer trigger still active.
>>>>
>>>> This patch fixes the problem by changing led_set_brightness()
>>>> to not initiate the delayed blink stop when brightness is not 0.
>>>
>>> Could we get this part of API documented? It is quite non-obvious... 0 clears the trigger,
>>> other values do not, I thought it is a bug when I saw it...
>> I guess the thinking was that if ON brightness differs
>> from OFF brightness, you should not clear the trigger.
>> But if you put ON brightness similar to OFF brightness,
>> then you can as well stop blinking at all.
>
> And none of this is documented. So what about this?

It is documented in Documentation/leds/leds-class.txt:

"However, if you set the brightness value to LED_OFF it will
also disable the timer trigger".

Nonetheless, obviously it should be also covered in the
ABI documentation.

>
> diff --git a/Documentation/ABI/testing/sysfs-class-led b/Documentation/ABI/testing/sysfs-class-led
> index 3646ec8..b734d7f 100644
> --- a/Documentation/ABI/testing/sysfs-class-led
> +++ b/Documentation/ABI/testing/sysfs-class-led
> @@ -4,16 +4,25 @@ KernelVersion:	2.6.17
>   Contact:	Richard Purdie <rpurdie@...ys.net>
>   Description:
>   		Set the brightness of the LED. Most LEDs don't
> -		have hardware brightness support so will just be turned on for
> +		have hardware brightness support, so will just be turned on for
>   		non-zero brightness settings. The value is between 0 and
>   		/sys/class/leds/<led>/max_brightness.
>
> +		Writing 0 to this file clears active trigger.
> +
> +		Writing non-zero to this file while trigger is active changes the
> +		top brightness trigger is going to use.

This currently will not be true e.g. for heartbeat trigger which
uses max_brightness.

> +		
> +
>   What:		/sys/class/leds/<led>/max_brightness
>   Date:		March 2006
>   KernelVersion:	2.6.17
>   Contact:	Richard Purdie <rpurdie@...ys.net>
>   Description:
> -		Maximum brightness level for this led, default is 255 (LED_FULL).
> +		Maximum brightness level for this LED, default is 255 (LED_FULL).
> +
> +		If the LED does not support different brightness levels, this
> +		should be 1.
>
>   What:		/sys/class/leds/<led>/trigger
>   Date:		March 2006
> @@ -21,7 +30,7 @@ KernelVersion:	2.6.17
>   Contact:	Richard Purdie <rpurdie@...ys.net>
>   Description:
>   		Set the trigger for this LED. A trigger is a kernel based source
> -		of led events.
> +		of LED events.
>   		You can change triggers in a similar manner to the way an IO
>   		scheduler is chosen. Trigger specific parameters can appear in
>   		/sys/class/leds/<led> once a given trigger is selected.
>


-- 
Best Regards,
Jacek Anaszewski
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