linux-kernel - RE: [PATCH] leds: leds-dual-gpio: Add dual GPIO LEDs driver

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Date:   Fri, 12 Mar 2021 08:48:55 +0000
From:   Hermes Zhang <Hermes.Zhang@...s.com>
To:     Alexander Dahl <ada@...rsis.com>,
        "linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>
CC:     Pavel Machek <pavel@....cz>, Dan Murphy <dmurphy@...com>,
        kernel <kernel@...s.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Marek Behun <marek.behun@....cz>
Subject: RE: [PATCH] leds: leds-dual-gpio: Add dual GPIO LEDs driver

Hi Alexander,

> Am Donnerstag, 11. März 2021, 14:04:08 CET schrieb Hermes Zhang:
> > From: Hermes Zhang <chenhuiz@...s.com>
> >
> > Introduce a new Dual GPIO LED driver. These two GPIOs LED will act as
> > one LED as normal GPIO LED but give the possibility to change the
> > intensity in four levels: OFF, LOW, MIDDLE and HIGH.
> 
> Interesting use case. Is there any real world hardware wired like that you
> could point to?
> 

Yes, we have the HW, it's not a chip but just some circuit to made of.
 
> > +config LEDS_DUAL_GPIO
> > +	tristate "LED Support for Dual GPIO connected LEDs"
> > +	depends on LEDS_CLASS
> > +	depends on GPIOLIB || COMPILE_TEST
> > +	help
> > +	  This option enables support for the two LEDs connected to GPIO
> > +	  outputs. These two GPIO LEDs act as one LED in the sysfs and
> > +	  perform different intensity by enable either one of them or both.
> 
> Well, although I never had time to implement that, I suspect that could
> conflict if someone will eventually write a driver for two pin dual color LEDs
> connected to GPIO pins.  We actually do that on our hardware and I know
> others do, too.
> 
> I asked about that back in 2019, see this thread:
> 
> https://www.spinics.net/lists/linux-leds/msg11665.html
> 
> At the time the multicolor framework was not yet merged, so today I would
> probably make something which either uses the multicolor framework or at
> least has a similar interface to userspace. However, it probably won't surprise
> you all, this is not highest priority on my ToDo list. ;-)
> 
> (What we actually do is pretend those are separate LEDs and ignore the
> conflicting case where both GPIOs are on and the LED is dark then.)
> 

Yes, that case seems conflict with mine, the pattern for me is like:

P1 | P2 | LED
-- + -- + -----
 0 |  0 | off
 0 |  1 | Any color
 1 |  0 | Any color
 1 |  1 | both on

Now I'm investigate another way from Marek's suggestion by using REGULATOR_GPIO, to see if could meet my requirement. If yes, then I do think no new  driver is needed.

Best Regards,
Hermes