[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...

There have been 3 crashes uploaded related to v5.10.9, and in all 3
cases the ACTHD has been in the first page. This strongly suggests that
the w/a is scribbling over address 0. And there's then a very good
chance that

commit 29d35b73ead4e41aa0d1a954c9bfbdce659ec5d6
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Mon Jan 25 12:50:33 2021 +0000

    drm/i915/gt: Always try to reserve GGTT address 0x0
    
    commit 489140b5ba2e7cc4b853c29e0591895ddb462a82 upstream.

in v5.10.14 is sufficient to hide the issue.
-Chris