linux-kernel - Re: [PATCH v3 09/11] platform/x86: asus-wmi: Control RGB keyboard backlight

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Message-ID: <20190509223436.GB527@amd>
Date:   Fri, 10 May 2019 00:34:37 +0200
From:   Pavel Machek <pavel@....cz>
To:     Dan Murphy <dmurphy@...com>
Cc:     Yurii Pavlovskyi <yurii.pavlovskyi@...il.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        Corentin Chary <corentin.chary@...il.com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Daniel Drake <drake@...lessm.com>,
        acpi4asus-user <acpi4asus-user@...ts.sourceforge.net>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-api@...r.kernel.org
Subject: Re: [PATCH v3 09/11] platform/x86: asus-wmi: Control RGB keyboard
 backlight

Hi!

> >> Yes, please. We have common interface for LED drivers; this needs to
> >> use it.
> > 
> > That is indeed a better option and I did in fact considered this first and
> > even did a test implementation. The discoveries were:
> > 1. The WMI methods are write-only and only written all at once in a
> > transaction manner (also invoking solely first RGB-interface method has no
> > effect until some other keyboard backlight method is called).

Write-only is not a problem, right? Nor should be transaction. Just
cache the values in kernel.

> > 2. In addition to RGB there are several control values, which switch
> > effects, speed and enable or disable the backlight under specific
> > conditions or switch whether it is set temporarily or permanently (not that
> > these are critical functionalities, but for the sake of
> > completeness).

Yep, lets ignore that for now.

> > 3. The EC is really slow
> > # time bash -c "echo 1 > /sys/devices/platform/faustus/kbbl_set"
> > 
> > real	0m0,691s
> > user	0m0,000s
> > sys	0m0,691s
> > 
> > (please ignore the sysfs-path there, it's essentially the same code running
> > as in this patch). It is consistently same for both temporary and permanent
> > configuration. Writing after every change would take about (6+)x of that.
> > Not that it's that unbearable though as it is not likely to be
> > done often.

Yup, this is quite ugly.

What about simply ignoring changes as they happen, and then setting
RGB channels when nothing changes for 10msec?

> > I was not quite happy with that implementation so I opted for writing sort
> > of sysfs wrapper instead that would allow same sort of transactions as
> > provided by BIOS. I agree that it's non-standard solution.
> > 
> > If I understood correctly, the typical current RGB led_class devices from
> > the Linux tree currently provide channels as separate LEDs. There are also
> > blink / pattern options present, I guess one could misuse them for setting
> > effects and speed. So one could make 3 devices for RGB + 3 for awake,
> > sleep, boot modes + 1 for setting effect / speed.

Take a look at "pattern" trigger. That should give you effect/speed
options. .. for single channel.

> > I'd guess the end solution might be also either something like combination
> > of both approaches (RGB leds + separate sysfs interface) or some extension
> > of the led_class device interface. Dropping support of the non-essential
> > features for the sake of uniformity of ABI would also be an option to
> > consider (exposing just three RGB LEDs with brightness only), not happy one
> > though.
> > 
> > In any case this looks like it might need some additional research,
> > discussion, development, and a pair of iterations so I tend to separate
> > this patch from the series and post it extra after the others are through
> > to avoid dragging 10+ patches around.

Separate patch certainly makes sense.

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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