** Changed in: xorg-server
Status: Unknown => Fix Released
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https://bugs.launchpad.net/bugs/1892136
Title:
reverse prime produces corrupted output on specific resolutions
Status in X.Org X server:
Fix Released
Status in xorg-server package in Ubuntu:
Fix Released
Status in xorg-server source package in Focal:
Fix Committed
Status in xorg-server source package in Hirsute:
Fix Released
Status in xorg-server source package in Impish:
Fix Released
Bug description:
The issue has initially been discovered for resolution 1366x768 on a
DisplayLink (evdi)-backed device, but applies also to UDL, as well as
reverse prime setups (rendering on Intel, output through NVidia).
The issue manifests with 1366x768 and several other resolutions only,
due to the fact that the GPU seems to use 64-aligned framebuffer
stride. This is "accidentally" fine with the most popular VGA
resolutions (e.g. assuming 32bits/4bytes per pixel and FullHD, the
stride would be 1920*4 -> 7680, which is divisible by 64 w/o a
remainder, yet 1366*4=5464, 5464/64 = 85.375). The proposed fix is to
update the stride with the GPU-provided value instead of the Xorg-
calculated one at the stage of sharing the pixmap between GPUs. Doing
that at earlier stage would probably require distinguishing between
allocation of a FB and a generic pixmap, which is the same for Xorg.
Issue for sure was seen on 18.04 and 19.04, probably still there for
20.04.
Upstream report:
https://gitlab.freedesktop.org/xorg/xserver/-/issues/889
And posted (not yet integrated) fix:
https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/496
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