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

[Hans de Goede]

Hi,

On 2/9/21 12:27 AM, Chris Wilson wrote:
> Quoting Hans de Goede (2021-02-08 20:38:58)
>> 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:
> 
> I tried to reproduce this on the w/e on hsw-gt1, to no avail; and piglit
> did not report any differences with and without mitigations. I have yet
> to test other platforms. So I don't yet have an alternative. Though note
> that v5.11 and v5.12 will behave similarly, so we need to urgently find
> a fix for Linus's tree anyway.

Note I've gone ahead and prepared a test kernel for the Fedora bug reports
with the following 3 commits reverted from 5.10.y :

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)

I know going this route is not ideal but it might be best for 5.10.y for now.

I will let you know if reverting these 3 actually helps once I hear back
from the reporters of the issue.

Regards,

Hans