Patch for "backlight: unable to request PWM" on MNT Reform Raspberry Pi CM4 SoM

Only after a recent dist-upgrade I ran into an issue w/ the screen staying dark b/c of pwm-backlight backlight: unable to request PWM on my Reform using the RCM4 Processor Module Adapter and a Raspberry Pi CM4:

# dmesg | grep backlight
[    6.202666] OF: /backlight: #pwm-cells = 3 found 2
[    6.202710] of_pwm_get(): can't parse "pwms" property
[    6.202721] pwm-backlight backlight: unable to request PWM

I found a related Raspberry Pi forum post: Kernel 6.6.0 - PWM seems not working/available

As it stands, it seems upstream change has broken it:

I was able to fix —patch— it like so:

git clone
cd mnt-reform-raspberry-pi-cm4-som

vi rcm4-overlay.dts
- pwms = <&pwm 0 10000>;
+ pwms = <&pwm 0 10000 0>;

sudo cp /boot/firmware/overlays/rcm4-overlay.dtbo /boot/firmware/overlays/rcm4-overlay.dtbo.old
sudo cp rcm4-overlay.dtbo /boot/firmware/overlays/rcm4-overlay.dtbo

sudo reboot

I’m reporting this here, b/c at least for now, it seems I couldn’t figure out how to contribute this patch to reform/mnt-reform-raspberry-pi-cm4-som.


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Thanks for sharing this! To contribute code, you can sign up on and then write an email with your username (and your plan) there to Or alternatively, create a full patch (for example commit the change locally incl your authorship info) and use, for example git format-patch -1 HEAD and post the patch here.

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