Comment # 46 on bug 39550 from Roy

Created attachment 85012 [details] [review]
drm/nv50: Fix backlight not working when PWM_DIV is uninitialised (v2)

V2 fixes the reach of this patch.
From what I can tell the PWM_DIV is simply a divider for the initial PWM clock
or something, it does not affect the scope of the duty cycle. I therefore
assume 0x5e is always a good value to set. Traces from NV50:NVA0 would help
verify whether NVIDIA always sets this value or not.
This patch requires acpi_backlight=vendor to be set because it tests for the
presence of a backlight by testing drm->backlight. An alternative to this test
would be checking for the GPIO to be present and routed to SOR, but I wouldn't
be surprised if there is at least one device that expects our driver to route
it manually. How should we go about this?