linux-kernel - Re: [PATCH 1/2] leds: Add driver for Qualcomm LPG

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Message-ID: <20170407133223.GE4756@amd>
Date:   Fri, 7 Apr 2017 15:32:23 +0200
From:   Pavel Machek <pavel@....cz>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Rob Herring <robh@...nel.org>,
        Richard Purdie <rpurdie@...ys.net>,
        linux-kernel@...r.kernel.org, linux-leds@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, Mark Rutland <mark.rutland@....com>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH 1/2] leds: Add driver for Qualcomm LPG

Hi!

> > In both RGB and pattern approaches we should assess
> > if it is acceptable to provide a pattern for trigger name,
> > e.g. blink-pattern-{num_intervals}.
> > 
> > If so, then "echo transition-pattern-15" would create a directory
> > e.g. transition_intervals with files interval_0 to interval_14,
> > that could be adjusted by userspace.
> 
> Having a RGB-trigger that proxy a accepts a userspace request of a
> brightness-tripple and sets the brightness on the individual associated
> LEDs sounds reasonable - but should probably be generalized to any
> number of LEDs.

Well..  Generalizing for any number of leds would be nice -- because
hardware can do that. OTOH, if we do that, we'll not have a place
where to do "white-adjustment".

> A slightly related matter is the question on how to use a single LED for
> multiple trigger sources, e.g. how do I get a single LED to show
> activity of two MMCs?.

We normally don't do that. We'd either have a trigger for a single
MMC, or trigger of all the MMCs..

> For the patterns I don't know how a trigger for this would look like,
> how would setting the pattern of a trigger be propagated down to the
> hardware?

Well... I'm not sure if we _want_ to do triggers for
patterns. LED triggers change rather quickly (100 times a second?) so
doing them in kernel makes sense. Patterns take 10s of seconds, so we
do not need to handle them in kernel. 

Thanks,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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