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

[Chris Wilson]

Quoting Hans de Goede (2021-02-09 11:46:46)
> 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?

The current one is headless, I'm trying to get a laptop with gt2 setup
again so that I can do more than test with piglit.

> 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.

It gives a clue that it's still a problem with the pipe state. (Which is
believable as there can't be much else!)
-Chris