Brightness too high on internal AMD/ATI graphics device, but fine with external AMD/ATI graphics card

[Alex Deucher]

On Sat, Jul 5, 2014 at 3:42 AM, Paul Menzel
<paulepanter at users.sourceforge.net> wrote:
> Dear Linux folks,
>
>
> connecting a VGA monitor to the internal graphics device of the ASRock
> E350M1 [1], the brightness is much too high.
>
>         $ lspci -tvnn
>         […]
>         +-01.0  Advanced Micro Devices [AMD] nee ATI Wrestler [Radeon HD 6310] [1002:9802]
>         +-01.1  Advanced Micro Devices [AMD] nee ATI Wrestler HDMI Audio [Radeon HD 6250/6310] [1002:1314]
>         […]
>
> Plugging in an external AMD/ATI graphics card and connecting the VGA
> monitor there, the brightness is normal as expected.
>
>         $ lspci -nn
>         […]
>         01:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ATI] Cedar [Radeon HD 5000/6000/7350/8350 Series] [1002:68f9]
>         01:00.1 Audio device [0403]: Advanced Micro Devices, Inc. [AMD/ATI] Cedar HDMI Audio [Radeon HD 5400/6300 Series] [1002:aa68]
>         […]
>
> The software stack is the same. Any idea how I can configure or debug
> that? This has been verified with 3.2.x to 3.14.9.

It sounds like the DAC bg/adj values are wrong on that board (they are
tuned on a per board basis and stored in the bios).  You might try a
bios upgrade on the board if there is one available.  If not, please
file a bug (https://bugs.freedesktop.org) and attach a copy of your
dmesg output, the vbios from the problematic board, and if possible
the output of `radeonreg regs dce4`.

To get a copy of your vbios:
(as root)
(use lspci to get the bus id)
cd /sys/bus/pci/devices/<pci bus id>
echo 1 > rom
cat rom > /tmp/vbios.rom
echo 0 > rom

You can get radeonreg here:
http://cgit.freedesktop.org/~airlied/radeontool/

Alex