[Intel-gfx] [5.10.y regression] i915 clear-residuals mitigation is causing gfx issues

[Hans de Goede]

Hi All,

We (Fedora) have been receiving reports from multiple users about gfx issues / glitches
stating with 5.10.9. All reporters are users of Ivy Bridge / Haswell iGPUs and all
reporters report that adding i915.mitigations=off to the cmdline fixes things, see:

https://bugzilla.redhat.com/show_bug.cgi?id=1925346

Which should be fully visible without a bugzilla account.

I noticed that 5.10.13 had one more related i915 patch, so I've asked the reporters
to retest with 5.10.13, 5.10.13 is better, but things are not fixed there, it just
takes longer for the problems to show up.

Greg, I can prepare a Fedora test-kernel build for the reporters to test with
the following 3 commits reverted:

520d05a77b2866eb ("drm/i915/gt: Clear CACHE_MODE prior to clearing residuals")
ecca0c675bdecebd ("drm/i915/gt: Restore clear-residual mitigations for Ivybridge, Baytrail")
48b8c6689efa7cd6 ("drm/i915/gt: Limit VFE threads based on GT")
(Note this are the 5.10.y hashes)

Reverting these 3 is not ideal, but it is probably the fastest way to get
this resolved for the 5.10.y series.

Greg, do you want me to have the reporters test a 5.10.y series kernel
with these 3 reverts ?

Regards,

Hans