[Intel-gfx] [PATCH] drm/i915/gt: Program mocs:63 for cache eviction on gen9

[Jason Ekstrand]

I just pulled drm-tip with both this and "drm/i915/gt: Declare gen9
has 64 mocs entries!" and the hang persists.  You really had my hopes
up there....  I think we need to merge the L3$ disable patch.

--Jason


On Thu, Nov 26, 2020 at 9:50 AM Ville Syrjälä
<ville.syrjala at linux.intel.com> wrote:
>
> On Thu, Nov 26, 2020 at 02:08:41PM +0000, Chris Wilson wrote:
> > Ville noticed that the last mocs entry is used unconditionally by the HW
> > when it performs cache evictions, and noted that while the value is not
> > meant to be writable by the driver, we should program it to a reasonable
> > value nevertheless.
> >
> > As it turns out, we can change the value of mocs:63 and the value we
> > were programming into it would cause hard hangs in conjunction with
> > atomic operations.
> >
> > v2: Add details from bspec about how it is used by HW
> >
> > Suggested-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2707
> > Fixes: 3bbaba0ceaa2 ("drm/i915: Added Programming of the MOCS")
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > Cc: Jason Ekstrand <jason at jlekstrand.net>
> > Cc: <stable at vger.kernel.org> # v4.3+
> > ---
> >  drivers/gpu/drm/i915/gt/intel_mocs.c | 14 +++++++++++++-
> >  1 file changed, 13 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/intel_mocs.c b/drivers/gpu/drm/i915/gt/intel_mocs.c
> > index 254873e1646e..26cedde80476 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_mocs.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_mocs.c
> > @@ -131,7 +131,19 @@ static const struct drm_i915_mocs_entry skl_mocs_table[] = {
> >       GEN9_MOCS_ENTRIES,
> >       MOCS_ENTRY(I915_MOCS_CACHED,
> >                  LE_3_WB | LE_TC_2_LLC_ELLC | LE_LRUM(3),
> > -                L3_3_WB)
> > +                L3_3_WB),
> > +
> > +     /*
> > +      * mocs:63
> > +      * - used by the L3 for all its evictions.
> > +      *   Thus it is expected to allow LLC cacheability to enable coherent
> > +      *   flows to be maintained.
> > +      * - used to force L3 uncachable cycles.
> > +      *   Thus it is expected to make the surce L3 uncacheable.
>
> "surce"?
>
> > +      */
> > +     MOCS_ENTRY(63,
> > +                LE_3_WB | LE_TC_1_LLC | LE_LRUM(3),
> > +                L3_1_UC)
> >  };
> >
> >  /* NOTE: the LE_TGT_CACHE is not used on Broxton */
> > --
> > 2.20.1
>
> --
> Ville Syrjälä
> Intel