[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.

Note the original / first reporter of:

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

Is using hsw-gt2, so it seems that the problem is not just the enabling of
the mitigations on ivy-bridge / bay-trail but that there actually is
a regression on devices where the WA worked fine before...

If you have access to a hsw-gt2 device then testing there might help?

Also note that this reproduces more easily on 5.10.10, which does not have:

520d05a77b2866eb ("drm/i915/gt: Clear CACHE_MODE prior to clearing residuals")

Not sure if that helps though.

> Though note
> that v5.11 and v5.12 will behave similarly, so we need to urgently find
> a fix for Linus's tree anyway.

Ack.

Regards,

Hans