[Bug 90151] Laptop Backlight Issue with Hybrid Graphics System

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=90151

--- Comment #5 from Alex Deucher <alexdeucher at gmail.com> ---
(In reply to Kevin Sarendranath from comment #0)
> The system being used is a Lenovo Thinkpad configured with an R7 M260DX
> discrete card attached to an A10-7300. Upon booting it, the kernel spits out
> this message:
> 
> 
> [drm:radeon_acpi_init [radeon]] *ERROR* Cannot find a backlight controller
> 

This message is from the dGPU which is not connected to any displays so it can
be ignored.  The backlight control is properly initialized on the APU which is
the chip that controls the backlight.

[    2.419773] [drm] radeon atom DIG backlight initialized

> 
> with the quirk of having the brightness hotkeys not being able to control
> the brightness. Looking into the radeon source, here is where the call came
> from (radeon_acpi.c):

What the brightness keys do is up to the OEM.  On most modern laptops, they
tend to just generate key press events rather than actually changing the
brightness or generating acpi events.  It's up to the desktop environment to
map that event to the brightness controls exposed by the kernel.

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