[Intel-gfx] [PATCH] drm/i915: Disable SAMPLER_STATE prefetching on all Gen11 steppings.

[Kenneth Graunke]

The Demand Prefetch workaround (binding table prefetching) only applies
to Icelake A0/B0.  But the Sampler Prefetch workaround needs to be
applied to all Gen11 steppings, according to a programming note in the
SARCHKMD documentation.

Using the Intel Gallium driver, I have seen intermittent failures in
the dEQP-GLES31.functional.copy_image.non_compressed.* tests.  After
applying this workaround, the tests reliably pass.

BSpec: 9663
Cc: stable at vger.kernel.org
Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 drivers/gpu/drm/i915/gt/intel_workarounds.c | 5 +++++
 1 file changed, 5 insertions(+)

(resending with S-o-b added...)

Hi there!

We tried to work around this in the Mesa driver, and managed to do so
in i965, anv, iris, but missed doing so in blorp.  Oops!  I'm planning
on fixing that, but setting the SARCHKMD bit to shut off the broken
prefetching globally seems like a good idea.  That way, we make sure it
works for i965, anv, iris, libva, and all the other userspace drivers.

FWIW, I don't have commit access, so I would appreciate it if someone
could commit this for me assuming it clears review and testing.

 --Ken

diff --git a/drivers/gpu/drm/i915/gt/intel_workarounds.c b/drivers/gpu/drm/i915/gt/intel_workarounds.c
index c70445adfb02..a3cb35d058a6 100644
--- a/drivers/gpu/drm/i915/gt/intel_workarounds.c
+++ b/drivers/gpu/drm/i915/gt/intel_workarounds.c
@@ -1254,6 +1254,11 @@ rcs_engine_wa_init(struct intel_engine_cs *engine, struct i915_wa_list *wal)
 				    GEN7_SARCHKMD,
 				    GEN7_DISABLE_DEMAND_PREFETCH |
 				    GEN7_DISABLE_SAMPLER_PREFETCH);
+
+		/* Wa_1606682166:icl */
+		wa_write_or(wal,
+			    GEN7_SARCHKMD,
+			    GEN7_DISABLE_SAMPLER_PREFETCH);
 	}
 
 	if (IS_GEN_RANGE(i915, 9, 11)) {
-- 
2.22.0