[Bug 202445] amdgpu/dc: framerate dropping below adaptive sync range causes screen flickering

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=202445

--- Comment #17 from Nicholas Kazlauskas (nicholas.kazlauskas at amd.com) ---
I can reproduce the issue but vsync needs to be on. I'd recommend turning vsync
off for now to avoid flickering.

The issue lies in how amdgpu_dm handles waiting for vblank and how userspace
interacts with the vblank counter in variable refresh rate mode.

The routine that does the wait / flip programming tries to aim for the next
vblank interval based on the current counter which rolls around at the vback
porch. If the routine gets delayed past scanout and into the front porch what
can happen is we're stuck waiting for the current vblank interval to timeout,
which will force the monitor to the lowest refresh rate and introduces
stuttering / flickering in this case.

There should be a fix for this soon.

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