On Fri, Dec 10, 2021 at 05:22:54PM -0800, Matt Roper wrote:
On Thu, Dec 09, 2021 at 09:21:39AM -0800, Lucas De Marchi wrote:
On Fri, Dec 03, 2021 at 08:26:03PM +0530, ravitejax.goud.talla@xxxxxxxxx wrote:
> From: Raviteja Goud Talla <ravitejax.goud.talla@xxxxxxxxx>
>
> Bspec page says "Reset: BUS", Accordingly moving w/a's:
> Wa_1407352427,Wa_1406680159 to proper function icl_gt_workarounds_init()
> Which will resolve guc enabling error
>
> v2:
> - Previous patch rev2 was created by email client which caused the
> Build failure, This v2 is to resolve the previous broken series
>
> Reviewed-by: John Harrison <John.C.Harrison@xxxxxxxxx>
> Signed-off-by: Raviteja Goud Talla <ravitejax.goud.talla@xxxxxxxxx>
It seems like this patch is needed to be able to load GuC in ICL:
https://gitlab.freedesktop.org/drm/intel/-/issues/4067#note_1184951
And that is failing on Linus' master branch as of
2a987e65025e ("Merge tag 'perf-tools-fixes-for-v5.16-2021-12-07' of git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux")
and (at least) 5.15.*. Looking at the appropriate "Fixes" tag I found these commits:
1) 1cd21a7c5679 ("drm/i915: Add Wa_1407352427:icl,ehl") - original
commit adding the WA
2) 3551ff928744 ("drm/i915/gen11: Moving WAs to rcs_engine_wa_init()")
moving the WA to rcs_engine_wa_init()
However (2) is on v5.7-rc1 and (1) is on v5.6-rc1 and according to the
bug report GuC loading was working on 5.13. So I suspect the move
to GuC 62.0.0 made the checks more strict, or there is another patch
This is correct. Having "GT workarounds" on the engine list by accident
used to be harmless (because i915 [with execlist submission] and the guc
[with guc submission]) would simply re-apply the register setting more
often than it really needed to. However the more recent GuC versions
have become more picky about the set of registers they're willing to
save/restore for workarounds and will fail to load if they see a
register on the save/restore list that isn't something they think is
appropriate for an engine reset.
GuC submission isn't officially supported on ICL; you can force it via
module parameter, which taints the kernel and takes you through untested
codepaths, so you do so at your own risk. Given that, I don't think
there's any real need to worry about getting this backported to specific
stable kernels; having the workaround in the wrong place doesn't
actually harm anything on the official and default non-GuC mode.
the discussion on gitlab sidetracked talking about GuC submission. This
is _not_ about GuC submission though: it's enable_guc=2 so it's simply
being used to load HuC.
Given it's a trivial move of the WA to the _right_ place that allows
people to continue using HuC as they were, I strongly disagree with
that statement. Yes, people use the module parameters at their own risk,
but we do fix it when it makes sense. If it was a pretty complex patch
we could decide to the other side of not porting it, but it's not the
case here.
Lucas De Marchi
