[Bug 204181] NULL pointer dereference regression in amdgpu

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=204181

--- Comment #44 from Sergey Kondakov (virtuousfox at gmail.com) ---
(In reply to Alex Deucher from comment #41)
> (In reply to Sergey Kondakov from comment #40)
> 
> > 
> > I little bit strange to call 2x1080p on AMD's fancy 5-port GPU (+ possible
> > DP multiplexing) "my issue". 
> 
> It's a limitation of desktop environments on Linux in general.  Other OSes
> handle this differently, but in general, regardless of OS, it's a hard
> problem to solve.  If you have multiple displays running at different
> refresh rates how do you update them without tearing and also without
> non-synchronized content on some of the displays?

I guess, you always would have to have at least 2
(currently_rendering/next_shown and previously_rendered/currently_shown)
buffers in an app, 2 per each viewport in compositor, 2 in each of system's
video output controllers (what if a viewport shares several outputs or vice
versa ?; "crtc" on GPU but I would prefer a tendency to simplification and
de-specialization of GPUs by replacing them with separate general-purpose
vector processors, rasterization or BVH ASICs, FPGA codec accelerators, output
controllers, all with wider faster common system bus and RAM instead of
GPU-daughterboard-on-CPU's-MB monstrosities) and 2 in each display's controller
(the latter is especially a problem because of slow scalers wanting to do their
bad scaling and other in-display transformations while adding unpredictable
unknown latency). And then make them all work asynchronously with their own
safe timeframes for flipping.

(In reply to Michel Dänzer from comment #42)
>…
> The way forward to solve this is Wayland.

Thanks for detailed explanations, stuff like that should be in manuals. As for
Wayland, I even managed to launch Wayland LXQt sessions with kwin via sddm
where most things work. But something made me postpone transition to it
indefinitively, don't remember what exactly. But right now at least 2 reasons
would be: custom display modes (I want my 72-73 "free" fps on 60 fps
almost-trash-level displays and my CRT have to have its non-standard modes
defined manually) and per-display colour correction (with auto-generated and
custom profiles).

(In reply to Tom Seewald from comment #43)
> (In reply to Nicholas Kazlauskas from comment #24)
> > This should be fixed with the series linked below:
> > 
> > https://patchwork.freedesktop.org/series/64505/
> > 
> > But it still needs review and backporting to older kernels.
> 
> That patch series (applied to mainline 5.2.x) appears to fix the hangs on my
> RX 560 while playing video with vaapi acceleration.
> 
> It would be great if this could be back-ported.

Unfortunately, it didn't fix the page flip-triggered dereference for me. Do you
have page flip related errors in Xorg log on "modesetting" X driver ? With and
without it ?

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