linux-kernel - Various LED complexities was Re: [PATCH v5 05/26] leds: core: Add support for composing LED class device names

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Date:   Thu, 4 Jul 2019 00:05:26 +0200
From:   Pavel Machek <pavel@....cz>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     'Linus Walleij' <linus.walleij@...aro.org>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Rob Herring <robh@...nel.org>,
        Dmitry Torokhov <dtor@...gle.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Dan Murphy <dmurphy@...com>,
        Baolin Wang <baolin.wang@...aro.org>,
        Daniel Mack <daniel@...que.org>,
        Oleh Kravchenko <oleg@....org.ua>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Simon Shields <simon@...eageos.org>
Subject: Various LED complexities was Re: [PATCH v5 05/26] leds: core: Add
 support for composing LED class device names

On Fri 2019-06-28 13:30:30, David Laight wrote:
> From: Linus Walleij
> > Sent: 28 June 2019 09:46
> ...
> > A problem with LEDs is that it invites bikeshedding because it is too
> > relateable.
> 
> Bikeshedding leds :-)
> 
> It also isn't at all clear how to handle bi-colour and tri-colour leds.
> ISTR the usual interface lets you set the brightness, but more often
> leds are single brightness but multi-colour.
> Eg the ethernet 'speed' led which is (usually) off/orange/green.
> 
> Changing the brightness either means changing the current or using PWM.
> Both really require more hardware support than changing colours.
> 
> I've done some led driving (for a front panel) from a PLD (small FPGA).
> As well as the obvious things I did:
> - dim: 1/8th on at 80Hz.
> - flash: 1/8th on at 4Hz.
> - orange: 50-50 red-green at 80Hz on an RGB led.
> 
> There was also the 'ethernet activity' led which could either be driven
> by the hardware, or forced on/off/flash by the driver.
> If driven by the hardware, the software could read the current state.
> 
> None of this really fitted the Linux leds interface.

Well, we are working on some of those :-). But lets discuss that in
separate threads.

In particular we are working on triggers and RGB LEDs.

bi-color LEDs seem to handled as two separate LEDs. Not much expected
to change there.
									
									Pavel

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

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