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

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Date:	Thu, 14 May 2015 14:09:16 +0200
From:	Jacek Anaszewski <j.anaszewski@...sung.com>
To:	Stas Sergeev <stsp@...t.ru>
Cc:	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] leds: fix brightness changing when software blinking is
 active

On 05/14/2015 01:03 PM, Stas Sergeev wrote:
> 14.05.2015 13:33, Jacek Anaszewski пишет:
>>> Indeed, but with these changes there should be no requirement
>>> for disabling a soft-blink from hard-irq context, which is what
>>> I really wanted to have. What am I missing?
>> Please look at this [1]. Author mentions setting brightness
>> from sound-card irq handler.
>>
>> [1] http://www.spinics.net/lists/linux-leds/msg00006.html
> He points to the following (out-of-tree??) code:
> ---
>          if ((jiffies / HZ / 2) & 1)
>                  led_trigger_blink_oneshot(ledtrig_ide,
>                                  &ide_blink_delay, &ide_blink_delay, 0);
>          if ((jiffies / HZ / 4) & 1)
>                  led_trigger_event(ledtrig_ide, 100);
>          if ((jiffies / HZ / 8) & 1)
>                  led_trigger_event(ledtrig_ide, 0);
> ---
> I think the problem was that oneshot_trig_deactivate() was
> not doing led_stop_software_blink(led_cdev), and so he needed
> a work-queue for switching out from oneshot trigger.
> My patch fixes exactly that: now oneshot trigger does the
> proper cleanup itself.
> Do you think my patch is not enough to handle this case?
>

This problem is related to the issue of locking between hard IRQ
and Softirqs [1]. I've just discovered also that there had been already
an attempt [2] of using work queue internally in led_set_brightness,
but it wouldn't have found its way to the mainline. Probably for a
reason.

[1] 
https://www.kernel.org/pub/linux/kernel/people/rusty/kernel-locking/c188.html
[2] http://www.serverphorums.com/read.php?12,563432

-- 
Best Regards,
Jacek Anaszewski
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