[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 #45 from Sergey Kondakov (virtuousfox at gmail.com) ---
(In reply to Alex Deucher from comment #44)
> There is no support for analog displays in DC.

Which was a horrible decision. Luckily, decent DP->VGA adapters actually work
even with proper ≥1080p ≥85fps CRTs. But it still has some problems with DVI
ports and/or HDMI->DVI adapters or certain monitors. Seems my issue with no
output at all in UEFI mode was a separate one and has to do with BIOS's signing
DRM nonsense. Hacked VBIOS works fine with UEFI… if you don't count just
initializing sole DP port at boot… which has backup/special-purpose CRT
connected and not real primary display in DVI.

But in either mode with dc=1 it just doesn't want to acknowledge my BENQ
G2320HDB connected with a simple HDMI->DVI adapter, as if it doesn't exist, and
there is no second DVI port. Maybe HDCP shenanigans ?

There is also another issue with amdgpu failing to initialize and hanging
display output at boot, if 64-bit PCIe addressing ("above 4G decoding") is
enabled, unless pcie=nocrs specified for kernel but that's a third issue and
likely has to do with crappy BIOS of my new unlicensed LGA2011 motherboard
(even though it works fine on Windows):
amdgpu: [powerplay] 
 failed to send message 254 ret is 0 
amdgpu: [powerplay] SMU load firmware failed
amdgpu: [powerplay] fw load failed
smu firmware loading failed
amdgpu 0000:03:00.0: amdgpu_device_ip_init failed
amdgpu 0000:03:00.0: Fatal error during GPU init
[drm] amdgpu: finishing device.

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