[PATCH] drm/i915/gt: Avoid duplicating CCS mode workaround

[Andi Shyti]

On Tue, Mar 25, 2025 at 01:57:42PM +0100, Chris Wilson wrote:
> Quoting Andi Shyti (2025-03-25 13:01:37)
> > When generating workarounds for the CCS engine, specifically for
> > setting the CCS mode related to compute load balancing, the
> > function 'ccs_engine_wa_mode()' is called twice: once for the
> > render engine and once for the compute engine.
> > 
> > Add a check to ensure the engine class is compute before applying
> > the workaround to avoid redundant programming.
> > 
> > Suggested-by: Arshad Mehmood <arshad.mehmood at intel.com>
> > Signed-off-by: Andi Shyti <andi.shyti at linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/gt/intel_workarounds.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gt/intel_workarounds.c b/drivers/gpu/drm/i915/gt/intel_workarounds.c
> > index 116683ebe074..37251546b755 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_workarounds.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_workarounds.c
> > @@ -2897,7 +2897,9 @@ engine_init_workarounds(struct intel_engine_cs *engine, struct i915_wa_list *wal
> >          */
> >         if (engine->flags & I915_ENGINE_FIRST_RENDER_COMPUTE) {
> >                 general_render_compute_wa_init(engine, wal);
> > -               ccs_engine_wa_mode(engine, wal);
> > +
> > +               if (engine->class == COMPUTE_CLASS)
> > +                       ccs_engine_wa_mode(engine, wal);
> 
> FIRST_RENDER_COMPUTE is meant to only be on the first engine of either
> rcs or ccs (which share certain register domains), one engine.
> 
> It looks like that was broken by
> 
> 	commit 1bfc03b1375244f9029bb448ee8224b3b6dae99f
> 	Author: Lucas De Marchi <lucas.demarchi at intel.com>
> 	Date:   Tue Mar 19 23:03:03 2024 -0700
> 
> 	    drm/i915: Remove special handling for !RCS_MASK()

Aha! So the logic here[*] breaks the meaning of
I915_ENGINE_FIRST_RENDER_COMPUTE, becasue, other than PVC, we
forgot that we have DG2 that needs the special check that uses
!RCS_MASK().

I need then to restore the original check.

Thanks Chris!
Andi

[*]
-       if ((engine->class == COMPUTE_CLASS && !RCS_MASK(engine->gt) &&
-            __ffs(CCS_MASK(engine->gt)) == engine->instance) ||
-            engine->class == RENDER_CLASS)
+       if ((engine->class == COMPUTE_CLASS || engine->class == RENDER_CLASS) &&
+           __ffs(CCS_MASK(engine->gt) | RCS_MASK(engine->gt)) == engine->instance)