Bug 481489

Summary: kms_swrast DRI not working on i915
Product: [Plasma] kwin Reporter: airisama019
Component: eglAssignee: KWin default assignee <kwin-bugs-null>
Status: RESOLVED NOT A BUG    
Severity: normal CC: xaver.hugl
Priority: NOR    
Version First Reported In: unspecified   
Target Milestone: ---   
Platform: Arch Linux   
OS: Linux   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:

Description airisama019 2024-02-17 23:43:27 UTC 
SUMMARY
kms_swrast mesa DRI can't start plasma with "startplasma-wayland" on i915.


STEPS TO REPRODUCE
1. Install any distro
2. use i915 hardware
3. try to use kms_swrast DRI

OBSERVED RESULT
It tries to run but I only get a mouse I can move on a black screen.

EXPECTED RESULT
See plasma logo with the cog wheel and start plasma.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Arch linux
KDE Plasma Version: stable and plasma 6 RC2 tested

ADDITIONAL INFORMATION
I can run it with fake llvmpipe DRI instead = MESA_LOADER_DRIVER_OVERRIDE=llvmpipe
Gnome starts but can't launch any apps because "permission denied issues" but it will run if I start with root
Can also run gnome with the same env
Comment 1 Zamundaaa 2024-02-18 14:35:01 UTC 
That sounds like KWin is working fine, but plasmashell doesn't start. Which is the same situation as you have on Gnome, and also expected, since kms_swrast tries to allocate dumb buffers for rendering, which only KWin has permissions to do.

Because of that there is no point in running the session with kms_swrast. It's simply not suitable for that purpose.
Comment 2 airisama019 2024-02-18 15:42:27 UTC 
then how are you supposed to deal with things like sway refusing to run because llvmpipe is not a file
there is pixman renderer but are we not going to make a universal way for software rendering?
I am 4 year linux user but I just found that llvmpipe trick a few months ago and it wasn't on arch wiki or anything like that
I dont't really remember but maybe stack overflow or reddit.
Comment 3 Zamundaaa 2024-02-18 15:56:48 UTC 
What do you mean, "llvmpipe trick"? If hardware acceleration isn't available on the kms node, Mesa automatically uses llvmpipe?
Comment 4 airisama019 2024-02-18 16:07:00 UTC 
yeah but on 3rd gen intel gpu sometimes you just have to switch to llvmpipe
not having a clear way to do so like on cinammon is a pain.
Comment 5 Zamundaaa 2024-02-19 21:46:14 UTC 
What do you mean with "sometimes you just have to switch to llvmpipe"?
Comment 6 airisama019 2024-02-19 21:51:59 UTC 
because of the graphical glitches
if I recall correctly the output says it ran out shaders or instructions.
Comment 7 airisama019 2024-02-19 22:13:21 UTC 
anyway don't sweat about this and just make sure the MESA_LOADER_DRIVER_OVERRIDE=llvmpipe env still works on future updates.
it's not a big deal
Comment 8 Zamundaaa 2024-02-19 22:53:56 UTC 
Okay. In case that doesn't exist yet, I'd still recommend you to make a bug report about the driver issue you have problems with here: https://gitlab.freedesktop.org/mesa/mesa/-/issues
Comment 9 airisama019 2024-02-19 23:25:19 UTC 
? but I feel like it's more about the way the driver is used since gnome, sway and cinnamon has almost no graphical glitches
so maybe reporting there is not the right move
although it kinda of gets better every new version of mesa
so, to clarify you line of thought, you just use their api's and expect it to work?
if yes then maybe I should report it there
Comment 10 Zamundaaa 2024-02-19 23:28:36 UTC 
yes, please do report it to Mesa. Other compositors have different renderer architectures, use other buffer formats (10 bit per color with KWin vs 8 bit per color with others), different effects and so on and will trigger different driver code paths and thus different driver bugs than KWin.