[Bug 200695] Blank screen on RX 580 with amdgpu.dc=1 enabled (no displays detected)

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=200695

--- Comment #14 from Claude Heiland-Allen (claude at mathr.co.uk) ---
I checked out linux v4.19-rc4 from git, then reverted that commit - no change,
display goes blank about 5 seconds into boot.

I noticed something else in the dmesg (it was there in 4.19-rc1,rc2,rc3,rc4,rc4
with reverted commit, but not earlier versions):

[    5.109572] amdgpu: [powerplay] Failed to retrieve minimum clocks.
[    5.109577] amdgpu: [powerplay] Error in phm_get_clock_info 
[    5.109627] [drm] DM_PPLIB: values for Engine clock
[    5.109629] [drm] DM_PPLIB:   300000
[    5.109631] [drm] DM_PPLIB:   600000
[    5.109632] [drm] DM_PPLIB:   900000
[    5.109633] [drm] DM_PPLIB:   1145000
[    5.109634] [drm] DM_PPLIB:   1215000
[    5.109636] [drm] DM_PPLIB:   1257000
[    5.109637] [drm] DM_PPLIB:   1300000
[    5.109638] [drm] DM_PPLIB:   1366000
[    5.109640] [drm] DM_PPLIB: Validation clocks:
[    5.109641] [drm] DM_PPLIB:    engine_max_clock: 136600
[    5.109642] [drm] DM_PPLIB:    memory_max_clock: 200000
[    5.109644] [drm] DM_PPLIB:    level           : 8
[    5.109646] [drm] DM_PPLIB: values for Memory clock
[    5.109647] [drm] DM_PPLIB:   300000
[    5.109648] [drm] DM_PPLIB:   1000000
[    5.109649] [drm] DM_PPLIB:   2000000
[    5.109651] [drm] DM_PPLIB: Validation clocks:
[    5.109652] [drm] DM_PPLIB:    engine_max_clock: 136600
[    5.109653] [drm] DM_PPLIB:    memory_max_clock: 200000
[    5.109655] [drm] DM_PPLIB:    level           : 8
[    5.124083] [drm] Display Core initialized with v3.1.59!

The last (largest) value for "engine clock" and "memory clock" are 10x the
validation values for "engine clock max" and "memory clock max".  I see in the
amd/powerplay sources some values are in units of 10kHz, some in units of
1kHz(?) - maybe a conversion was missed somewhere? Or maybe the printout is
totally normal and I know nothing :)

The error message common to all kernels with amdgpu.dc=1 since 4.17 is:

[    5.256378] [drm] Cannot find any crtc or sizes

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