Couldn't read Speaker Allocation Data Block/SADs

[Jean Delvare]

Hi all,

Since I connected my Dell display on my Radeon R5 240 (Oland) card over
DisplayPort instead of VGA, I get the following error messages logged at every boot:

[drm:dce_v6_0_encoder_mode_set [amdgpu]] *ERROR* Couldn't read Speaker Allocation Data Block: -2
[drm:dce_v6_0_encoder_mode_set [amdgpu]] *ERROR* Couldn't read SADs: -2

I also see them each time the display wakes up and also on VT change.
This is with kernel 5.2.9.

This was also reported as bug #107825 by Paul Menzel:
https://bugs.freedesktop.org/show_bug.cgi?id=107825

Error -2 is ENOENT (No such file or directory). The driver queries the
display for audio-related information, while my display does not have
speakers nor headset connector.

I suspect that the "error" is pretty much expected in this case and the
driver is being too verbose about it. Either the calling code should
consider -ENOENT as a non-error (11 calling sites to fix), or the
helper functions should simply return 0 when no audio-related data is
available from the display (2 functions to fix, calling sites may have
to be inspected too as some treat 0 as an error too, which seems
incorrect to me).

Option 1 seems cleaner to me, but I don't know if there could be
legitimate reasons to distinguish between no audio information block
from display and empty audio information from display in the future.

What do you think?

Thanks,
-- 
Jean Delvare
SUSE L3 Support