Gregory's Server
Can anyone with more GPU knowledge tell me how that should even be possible
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8 comments
 @BrodieOnLinux I am by no means a GPU expert, but I think this is because cursors are rendered in a special layer that gets composed with all the other layers to create the final image, and for some reason that layer just didn't get disabled when switching. I've seen this many times when shutting down my system.
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today at 3:32 | Open on donotsta.re
 @BrodieOnLinux The part of a graphics chip that handles the HDMI output, aka the display controller, has several registers containing pointers into GPU memory. It composites several "planes" on top of each other in order to create the final output, each plane has an input framebuffer pointer configured in the registers. There are three main types of planes usually present -> the primary plane, which contains the output of the display server, the overlay plane, which usually contains (1/? π§΅) @BrodieOnLinux directly scanned-out surfaces (On Smithay-based compositors, this is usually the Wayland surface that's in focus), this allows eg. video playback with lower latency, and lastly, cursor planes, where you configure the location of the cursor with registers, and the bound framebuffer is the contents of the cursor plane. Linux lacks any kind of general DRM (Direct Rendering Manager) state management, so cleaning up into a known state is usually the job of a display server (2/? π§΅) @BrodieOnLinux If the display server crashes without being able to clean up (and if it actually has cleanup code; For example wlroots-based compositors don't have cleanup code even on VT switch, so if you eg. use Cosmic or Anvil and Sway in two VTs you'll get windows stuck on the screen), the display controller simply persists the current state and keeps rendering the cursor framebuffer which is still in VRAM. See also https://docs.kernel.org/gpu/drm-kms.html (3/? π§΅)  Yea this is the "hardware cursor" that display servers talk about when they offer an option between a software cursor (compositing the cursor themselves into the primary plane) and hardware cursor (managing a cursor plane) :P  |