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

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Date:   Fri, 12 Mar 2021 06:59:22 +0100
From:   Marek Behun <marek.behun@....cz>
To:     Hermes Zhang <Hermes.Zhang@...s.com>
Cc:     Pavel Machek <pavel@....cz>, Dan Murphy <dmurphy@...com>,
        kernel <kernel@...s.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>
Subject: Re: [PATCH] leds: leds-dual-gpio: Add dual GPIO LEDs driver

On Fri, 12 Mar 2021 04:48:52 +0000
Hermes Zhang <Hermes.Zhang@...s.com> wrote:

> > 
> > Sorry, leds-regulator has only a binary state LED.
> > 
> > Maybe you could extend leds-regulator to be able to use all regulator states?
> > 
> > Or you can extend leds-gpio driver to support N states via log N gpios,
> > instead of adding new driver.  
> 
> It seems a good idea to extend leds-gpio, so in my case, I should have such dts:
> 
>  63         leds {
>  64                 compatible = "gpio-leds";
>  65 
>  66                 recording_front {
>  67                         label = "recording_front:red";
>  68                         gpios = <&gpio 130 GPIO_ACTIVE_HIGH>, <&gpio 129 GPIO_ACTIVE_HIGH>;
>  69                         default-state = "off";
>  70                 };
>  71         };
> 
> For my case, two leds is enough, but it sill easy to extend the support number bigger than two. And the length of gpios array is not fixed, so it could compatible with exist "gpio-leds" dts, right? 
> 
> If this idea work, should I create a new commit or still in this track (V2)?

However you want :)

Look at the states property of gpio regulator:
https://www.kernel.org/doc/Documentation/devicetree/bindings/regulator/gpio-regulator.yaml

It is possible to have a multi-GPIO LED which brightness is set via N
GPIOs and it has 2^N brightness states encoded by binary values of
those GPIOs, but it is entirely possible to have less than 2^N states,
or that the states are encoded in a different way.

In the first version though imlpemenent just the simplest case: N GPIOs
with 2^N states.

Marek