linux-kernel - Re: [RESEND PATCH v17 00/17] Multi Color LED Framework

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Date:   Thu, 27 Feb 2020 11:58:08 +0100
From:   Pavel Machek <pavel@...x.de>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, Dan Murphy <dmurphy@...com>,
        linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH v17 00/17] Multi Color LED Framework

Hi, Jacek!

(and thanks for doing this).

> We have here long lasting discussion related to LED multicolor class
> sysfs interface design. We went through several iterations and worked
> out the solution with individual file per each color sub-LED in the
> color directory as shown below:
> 
> /sys/class/leds/<led>/colors/<color>_intensity
> 
> This is in line with one-value-per-file sysfs rule, that is being
> frequently highlighted, and we even had not so long ago a patch
> for led cpu trigger solving the problem caused by this rule not
> being adhered to.

Yep. One of the problems is that it is nice to change all the hardware
channels at once to produce color (it is often on i2c -- and slow), so
current proposals use "interesting" kind of latching.

> Now we have the voice below bringing to attention another caveat
> from sysfs documentation:
> 
> "it is socially acceptable to express an array of values of the same
> type"
> 
> and proposing the interface in the form of two files:
> 
> channel_intensity (file containing array of u32's)
> channel_names (usually containing "red green blue")

And thus I want to have it in one file, so it is naturaly atomic. RGB
leds with 3 channels are common; I have not user yet, but there are
RGBW with 4 channels (and some more exotic stuff). I don't expect to
have more than 5 channels.

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

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