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

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Date:   Thu, 27 Feb 2020 13:43:29 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Pavel Machek <pavel@...x.de>
Cc:     Jacek Anaszewski <jacek.anaszewski@...il.com>,
        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

On Thu, Feb 27, 2020 at 11:58:08AM +0100, Pavel Machek wrote:
> 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.

Writing 3 or 4 or 5 numbers all at once in a single sysfs file to
represent a single output should be fine.

thanks,

greg k-h