Subject: Re: [PATCH] leds: Allow drivers to update the core, and generate
 events on changes
To: Pavel Machek <pavel@ucw.cz>
References: <20161227191136.4516-1-gabriele.mzt@gmail.com>
 <20161227200755.GA6345@amd>
Cc: rpurdie@rpsys.net, jacek.anaszewski@gmail.com,
        linux-leds@vger.kernel.org, linux-kernel@vger.kernel.org
From: Gabriele Mazzotta <gabriele.mzt@gmail.com>
Message-ID: <5f442764-825b-1bdc-2763-1c4c8dc1c098@gmail.com>
Date: Tue, 27 Dec 2016 21:23:28 +0100
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On 27/12/2016 21:07, 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.

Oh, I didn't know that, sorry.

> LED can be updated many times per second, uevent is probably _not_
> good mechanism to achieve that.

Ummm, right, I didn't think of that.

> Generating uevent for /sys changes does not make much sense, right?

I planned to use this patch mostly for keyboard backlights, for
which some DEs provide a UI similar to the one for screen backlights.
Having uevents also for /sys changes means having the UI always in
sync with the kernel/hardware, as it happens for screen backlights.
In case of LEDs only the application changing the brightness is
aware of the change.

>> +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.

OK, I'll see if I can come up something good.

Regards,
Gabriele

> Best regards,
> 
> 								Pavel
>