linux-kernel - Re: [PATCH] leds: Allow drivers to update the core, and generate events on changes

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Message-ID: <3560132e-ac79-b6fa-200c-da9c7ed9d435@gmail.com>
Date:   Tue, 27 Dec 2016 23:57:26 +0100
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Pavel Machek <pavel@....cz>,
        Gabriele Mazzotta <gabriele.mzt@...il.com>
Cc:     rpurdie@...ys.net, linux-leds@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] leds: Allow drivers to update the core, and generate
 events on changes

Hi Gabriele, Pavel,

On 12/27/2016 09:07 PM, Pavel Machek wrote:
> Hi!
> 
>> Similarily to commit 325253a6b2de ("backlight: Allow drivers to update
>> the core, and generate events on changes"), inform userspace about
>> brightness changes and allow drivers to request updates of the
>> brightness value.
> 
> First... we had similar patch in tree, and it caused problems, we are
> now trying to figure out how to do it properly.
> 
> LED can be updated many times per second, uevent is probably _not_
> good mechanism to achieve that.
> 
> Generating uevent for /sys changes does not make much sense, right?
> 
>> +extern void led_brightness_force_update(struct led_classdev *led_cdev,
>> +				enum led_brightness_update_reason reason);
> 
> I see this may make some sense, but there are no uses for this in this
> patch.
> 
> My preffered solution would be ... for hardware that changes led
> brightness itself, introduce a "trigger", so that userspace knows this
> led is special, and then provide poll()able /sys fs file interested
> parties can read.

I've recently submitted for a discussion the idea of "persistent
triggers" [0]. Any feedback is very much appreciated.

[0] https://www.spinics.net/lists/linux-leds/msg07332.html

-- 
Best regards,
Jacek Anaszewski