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

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Message-ID: <20170410095207.GA4475@xo-6d-61-c0.localdomain>
Date:   Mon, 10 Apr 2017 11:52:08 +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!

> > Actually we could achieve the goal by listing all available pattern
> > configurations for given LED class device, so in case of Qualcomm LPG
> > driver we could have transition-pattern-1 to transition-pattern-15
> > listed after executing "cat trigger".
> > 
> 
> There's a common pattern-table of 24 (or 64) entries, that is shared
> among the 8 LPGs (each LPG simply has to indices pointing into the
> shared table). Each entry in the table holds a value between 0 and 511.
> So that's a lot of "available pattern configurations".

> > I wonder if I'm not missing some vital constraints here that could
> > make this design unfeasible.
> > 
> 
> Regardless of how we expose RGBs to userspace, the 8 LPG hardware blocks
> are independent of each other. The fact that they end up controlling
> something that is perceived by the human eye as some mixed color is to
> me a matter of system integration, and as such should not convolute the
> implementation of the individual instances.

Well... the 8 LPG blocks share the pattern-table.. and the pattern-table is very
limited. We could statically allocate 3 entries to each LPG block, but that
would not be too useful. And if we dynamically allocate entries depending on
patterns, then the LPG blocks are no longer independent.

									Pavel

-- 
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