Re: Graphical glitches (not refreshing?) with Linux's xe driver + Xen 4.19

["Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>]

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On Fri, Feb 13, 2026 at 02:23:06AM +0100, Marek Marczykowski-Górecki wrote:
> On Thu, Feb 12, 2026 at 04:11:50PM +0100, Roger Pau Monné wrote:
> > On Tue, Feb 10, 2026 at 07:06:20PM +0100, Marek Marczykowski-Górecki wrote:
> > > Hi,
> > > 
> > > Recently I started testing compatibility with Intel Lunar Lake. This is
> > > the first one that uses "xe" instead of "i915" Linux driver for iGPU.
> > > I test it with Qubes OS 4.3, which uses Xen 4.19.4 and PV dom0 running
> > > Linux 6.17.9 in this test.
> > 
> > Not sure it's going to help a lot, but does using a PVH dom0 make any
> > difference?
> 
> Ok, now with the correct Xen version, it's better with PVH dom0. At
> least on the login screen and few applications (from both dom0 and domU)
> I don't see the glitches anymore. I can't do a full test, because PCI
> passthrough doesn't seem to work with PVH dom0 on Xen 4.19 - and I need
> it to start most VMs.
> 
> So, if the above test is representative, it's only about PV dom0.

Some further observations:

1. My initial impression that Xen 4.17.6 is not affected is false.
Apparently I got lucky and didn't waited long enough for glitches to
appear. Unfortunately this means I have no way to bisect this...

1a. Updated test procedure - either:
  - start Qubes OS in full (including default system domUs) and try to
    open an app in one of them (for example file manager or pdf viewer)
  - start Linux up to lightdm login page, log in, log out, click on a
    few lightdm menus (session type selector, poewroff menu etc)

The second version works even if toolstack version in dom0 doesn't match
Xen version. If no glitches are observed after doing either of those
procedures, assume it's good.

2. Xen staging is affected too. As well as Xen staging-4.19 without
any qubes patches.

3. After enabling CONFIG_DEBUG in Xen, the xe.ko fails to load firmware:

    xe 0000:00:02.0: [drm] Tile0: GT0: Using GuC firmware from xe/lnl_guc_70.bin version 70.53.0
    xe 0000:00:02.0: [drm] *ERROR* Tile0: GT0: load failed: status = 0x40000056, time = 0ms, freq = 1850MHz (req 1850MHz), done = -1
    xe 0000:00:02.0: [drm] *ERROR* Tile0: GT0: load failed: status: Reset = 0, BootROM = 0x2B, UKernel = 0x00, MIA = 0x00, Auth = 0x01
    xe 0000:00:02.0: [drm] *ERROR* Tile0: GT0: firmware production part check failure
    xe 0000:00:02.0: [drm] *ERROR* Tile0: GT0: Failed to initialize uC (-EPROTO)
    xe 0000:00:02.0: probe with driver xe failed with error -71

CONFIG_DEBUG is the only change between "xe.ko loads fine but there are
glitches later on" and "xe.ko fails to load at all". Full console logs:
https://gist.github.com/marmarek/47b5e62a2cdbae6678c2aecc5283cd3f, there
are 3 files:
  - CONFIG_DEBUG=n
  - CONFIG_DEBUG=y
  - CONFIG_DEBUG=y + iommu=debug

4. Updating to Linux 7.0-rc1 doesn't help, for example:
https://openqa.qubes-os.org/tests/168119#step/desktop_linux_manager_create_qube/11

Generally, it does feel like a bug in xe.ko, but I can't exclude some issue
on Xen side too (especially given point 3 above).

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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