Re: [PATCH v5 2/6] leds: triggers: Add a keyboard backlight trigger

[Pavel Machek <pavel@ucw.cz>]

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Hi!

> >> There might exist users that adjust LED brightness while having
> >> active trigger. The best example is default-on trigger - it sets
> >> brightness only on init, but remains active all the time. Whereas
> >> this could be fixed, there is another case: think of changing blinking
> >> brightness - it would be impossible.
> > 
> > I don't see the breakage. For existing blinking and default-on
> > triggers, existing behaviour would be kept. Difference would be that
> > for hardware that changes triggers itself (like the keyboard light) we
> > would present it as a trigger. And you are right -- there would be
> > user visible changes there. You could not assign blinking, because
> > .. it already has a trigger. But I believe it is reasonable.
> 
> We've already received negative feedback regarding blocking
> application of different trigger when hw brightness change
> notifications

Actually sometimes we'll get negative feedback for anything we do. I
still believe exposing the backlight case as a trigger is a right thing.

> are enabled. One solution to that is making the notifications
> orthogonal to the trigger mechanism. The other possibility is to allow
> for having more than one active trigger for a LED.
> 
> We could think of defining a special type of persistent trigger that
> would be always enabled.

Yes, that could be done. I'd not call it persistent trigger, but
with right name...

#1:

Apparently some LEDs change themselves, and we can't find how or
when. That's thinkpad battery LED, for example.

#2:

Then there are some LEDs that change themselves, and we can get
notifications. We should make it very clear that we'll not send
notifications kernel did itself.

So... for #1 and #2 something like

led/hardware_changes_brightness 

and for #2

led/poll_for_hardware_brightness_change

where poll() wakes the userspace up when the brightness changes, and
read() can get new brightness...?
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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