https://bugs.kde.org/show_bug.cgi?id=524768
Bug ID: 524768
Summary: Treat tiled DisplayID monitors (e.g. 5K iMac panels)
as a single logical display
Classification: Plasma
Product: kwin
Version First 6.7.4
Reported In:
Platform: Debian testing
OS: Linux
Status: REPORTED
Severity: wishlist
Priority: NOR
Component: wayland-generic
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
Some hardware exposes a single physical panel as two separate DRM connectors
that must be tiled together to form one logical display — for example the 27"
5K iMac panel (2014–2019 models), which drives 5120x2880 as two 2560x2880 tiles
over two DisplayPort streams. The DisplayID tile information (base ID, tile
location, tile size, num tiles) is present in the EDID/DisplayID and is exposed
correctly at the DRM level.
Under X11, Xorg reads this tile information and automatically creates a single
RandR 1.5 "Monitor" object spanning both outputs. Under KWin/Wayland, and even
under KWin on X11, this tile grouping is not used — the two tiles are treated
as two fully independent screens.
Practical consequences on affected hardware:
Maximizing a window only fills one tile (half the panel), not the full
5120x2880 area
Fullscreen requests (video players, browser fullscreen) are only satisfied on
one tile
Edge snapping / quick tiling only spans one tile
The panel/taskbar only covers one tile's width
A visible seam/shadow appears between the two window edges when two separate
windows sit side by side
Steps to reproduce (on affected hardware):
Boot a kernel with tiled-display support for the panel in question (e.g.
https://github.com/mcirsta/linux-imac-5k for the iMac case)
Run xrandr -q — two connectors appear, each at half the native tile resolution
Under X11, xrandr --listmonitors shows both automatically grouped into one
Monitor by Xorg
Under KWin (X11 or Wayland), maximize/fullscreen a window — it only fills one
tile
Expected behavior: KWin recognizes the DisplayID tile grouping (or the RandR
Monitor object under X11) and treats the tiled pair as a single logical output
for maximize, fullscreen, edge snapping, and panel placement.
Additional context:
This is a known, tracked gap — see the draft merge request
https://invent.kde.org/plasma/kwin/-/merge_requests/1174 ("platforms/drm:
support tiled displays"), which has been open for an extended period. There is
also related community work on a custom kernel enabling 5K on pre-2020 iMacs
under Linux: https://github.com/mcirsta/linux-imac-5k, and discussion at
https://gitlab.freedesktop.org/drm/amd/-/issues/4455.
Environment:
Hardware: iMac19,1 (2019, 27" 5K), AMD Radeon RX 480 (Polaris, amdgpu)
Distro: Debian testing
Plasma version: 6.7.2, KWin, Wayland session
Kernel: custom linux-imac-5k build (7.0.1), required for native panel tiling on
this hardware
I'm happy to test patches or provide further logs — this is hardware that's
uncommon among developers (pre-2020 5K iMacs with a tiled internal panel), so
testers may be hard to come by.
--
You are receiving this mail because:
You are watching all bug changes.
