Combining multiple PWM LEDs into RGB LED?

Combining multiple PWM LEDs into RGB LED?

[Sven Schwermer]

Hi,

I'm wondering about the correct device tree syntax for organizing 
multiple PWM LEDs into a multi-color (RGB) LED. This is my device tree:

/ {
   rgb-led {
     pinctrl-names = "default";
     pinctrl-0 = <&pinctrl_leds>;
     compatible = "pwm-leds";
     multi-led@0 {
       color = <LED_COLOR_ID_RGB>;
       led-red {
         pwms = <&pwm1 0 1000000>;
         color = <LED_COLOR_ID_RED>;
         max-brightness = <65535>;
       };
       led-green {
         pwms = <&pwm2 0 1000000>;
         color = <LED_COLOR_ID_GREEN>;
         max-brightness = <65535>;
       };
       led-blue {
         pwms = <&pwm3 0 1000000>;
         color = <LED_COLOR_ID_BLUE>;
         max-brightness = <65535>;
       };
     };
   };
   /* ... */
};

My kernel complains as follows:

of_pwm_get(): can't parse "pwms" property
leds_pwm rgb-led: unable to request PWM for multi-led: -2
leds_pwm: probe of rgb-led failed with error -2

Is my syntax incorrect or is this not a use case that is currently 
supported? I should also note that I back-ported the multi-LED feature 
to 5.4.158 so I may have missed some relevant patches.

Any insight is appreciated.

Best regards,
Sven

Re: Combining multiple PWM LEDs into RGB LED?

[Alexander Dahl]

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Hello Sven,

On Thu, Jan 20, 2022 at 03:07:26PM +0100, Sven Schwermer wrote:
> I'm wondering about the correct device tree syntax for organizing multiple
> PWM LEDs into a multi-color (RGB) LED. This is my device tree:
> 
> / {
>   rgb-led {
>     pinctrl-names = "default";
>     pinctrl-0 = <&pinctrl_leds>;
>     compatible = "pwm-leds";
>     multi-led@0 {
>       color = <LED_COLOR_ID_RGB>;
>       led-red {
>         pwms = <&pwm1 0 1000000>;
>         color = <LED_COLOR_ID_RED>;
>         max-brightness = <65535>;
>       };
>       led-green {
>         pwms = <&pwm2 0 1000000>;
>         color = <LED_COLOR_ID_GREEN>;
>         max-brightness = <65535>;
>       };
>       led-blue {
>         pwms = <&pwm3 0 1000000>;
>         color = <LED_COLOR_ID_BLUE>;
>         max-brightness = <65535>;
>       };
>     };
>   };
>   /* ... */
> };
> 
> My kernel complains as follows:
> 
> of_pwm_get(): can't parse "pwms" property
> leds_pwm rgb-led: unable to request PWM for multi-led: -2
> leds_pwm: probe of rgb-led failed with error -2
> 
> Is my syntax incorrect or is this not a use case that is currently
> supported? I should also note that I back-ported the multi-LED feature to
> 5.4.158 so I may have missed some relevant patches.

AFAIK nodody implemented multicolor functionality for the LEDs PWM
driver yet.  I think it should go to drivers/leds/leds-pwm.c and I
would offer to test it, once anybody sends patches for this. O:-)

Greets
Alex

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Re: Combining multiple PWM LEDs into RGB LED?

[Jacek Anaszewski]

Hi Sven,

On 1/20/22 3:07 PM, Sven Schwermer wrote:
> Hi,
> 
> I'm wondering about the correct device tree syntax for organizing 
> multiple PWM LEDs into a multi-color (RGB) LED. This is my device tree:
> 
> / {
>    rgb-led {
>      pinctrl-names = "default";Hi Sven,
>      pinctrl-0 = <&pinctrl_leds>;
>      compatible = "pwm-leds";
>      multi-led@0 {
>        color = <LED_COLOR_ID_RGB>;
>        led-red {
>          pwms = <&pwm1 0 1000000>;
>          color = <LED_COLOR_ID_RED>;
>          max-brightness = <65535>;
>        };
>        led-green {
>          pwms = <&pwm2 0 1000000>;
>          color = <LED_COLOR_ID_GREEN>;
>          max-brightness = <65535>;
>        };
>        led-blue {
>          pwms = <&pwm3 0 1000000>;
>          color = <LED_COLOR_ID_BLUE>;
>          max-brightness = <65535>;
>        };
>      };
>    };
>    /* ... */
> };
> 
> My kernel complains as follows:
> 
> of_pwm_get(): can't parse "pwms" property
> leds_pwm rgb-led: unable to request PWM for multi-led: -2
> leds_pwm: probe of rgb-led failed with error -2
> 
> Is my syntax incorrect or is this not a use case that is currently 
> supported? I should also note that I back-ported the multi-LED feature 
> to 5.4.158 so I may have missed some relevant patches.
> 
> Any insight is appreciated.

leds-pwm driver doesn't have support for multicolor LEDs. You'd have to
write a new driver, say leds-pwm-multicolor.

-- 
Best regards,
Jacek Anaszewski