> The attached patch should fix it. pwm control is only available with dpm, and you've disabled dpm via the kernel command line.

Oh yes, the last grub update (fortuitously made the morning before I change my GPU for the one described above) introduced a "radeon.dpm=0" default kernel command line option, probably to workaround that other bug https://bugzilla.kernel.org/show_bug.cgi?id=103271

Thank you for your fast answer, I will try both (the patch and the kernel command line option).

On which source tree this patch must be applied?

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Thomas DEBESSE