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Compute Module • Re: Raspberry CM4 pwm-backlight duty cycle missing

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Hi, were you able to get this resolved? I’m running into the same issue where bl_power ends up as 4, and I suspect it might be related to the same lines in the kernel source you linked.
I ended up solving it in user-space with a systemd service enabling and setting the brightness.
Keep us updated if you figure out a better solution.
:?:
Well, you're both right in saying that loading your overlays will result in a PWM node being created - let's use the one labeled 'rpi_backlight'
What is claiming that resource? As long as no panel is using it it will not be set to active -> PWM duty will be zero. So, how do you assign that resource to your display device?

typ one would do that in the panel-node, by i.e.

Code:

panel: panel {        compatible = "some make, model";        backlight = <&rpi_backlight>;...}
then your backlight will be related to said display and will be active when your display is active.
Defining the backlight PWM node in the overlay which also configures the panel is way easier than exporting symbols ...

https://github.com/raspberrypi/linux/bl ... ml#L84-L85

So show me how you're doing that.

Statistics: Posted by aBUGSworstnightmare — Wed Jun 11, 2025 5:30 am



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