[Bug 208947] amdgpu DisplayPort won't recognize all display modes after 5.9 merges

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=208947

--- Comment #16 from Coleman Kane (ckane@colemankane.org) ---
Pulling the call / reassignment of "status" added in that commit seems to
revert the undesirable behavior, including in the latest "staging-testing" code
that I've tested on.

My hardware situation seems to be that the "native" resolution of my DP display
(3840x2160@60Hz) is also advertised as "supported" by the RX 580m on my laptop,
but for whatever reason the GPU is unable to actually drive that resolution. I
don't know enough about the hardware to speculate as to why this is, though.
Using the "video=" option to the kernel, I can force a functioning video mode,
which seems to be consistent with the intent of that variable, when this call
is commented out. However, if the call to check_link_loss_status happens, then
the inconsistent behavior occurs that I described above where it randomly might
work, might only give me 1024x768, or might never display on my DP-connected
monitor regardless of the resolution chosen.

That said, I wonder if it makes sense to wrap this call with another kernel
command-line boolean variable, so the behavior can be disabled in the event
someone has a misbehaving GPU or monitor like I do - unless you think there
might be a graceful way to auto-identify this type of defect. Not sure how the
auto-selection works for KMS console resolutions, but it would be helpful too
if it detected that an attempt at a high refresh rate didn't work, it
automatically tried lower refresh rates.

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