[Intel-gfx] [PATCH v2 2/3] drm/i915: Setup MCR steering for RCS engine workarounds

Matt Roper matthew.d.roper at intel.com
Sat May 2 04:57:43 UTC 2020

Reads of multicast registers give the value associated with
slice/subslice 0 by default unless we manually steer the reads to a
different slice/subslice.  If slice/subslice 0 are fused off in hardware,
performing unsteered reads of multicast registers will return a value of
0 rather than the value we wrote into the multicast register.

To ensure we can properly readback and verify workarounds that touch
registers in a multicast range, we currently setup MCR steering to a
known-valid slice/subslice as the very first item in the GT workaround
list for gen10+.  That steering will then be in place as we verify the
rest of the registers that show up in the GT workaround list, and at
initialization the steering will also still be in effect when we move on
to applying and verifying the workarounds in the RCS engine's workaround
list (which is where most of the multicast registers actually show up).

However we seem run into problems during resets where RCS engine
workarounds are applied without being preceded by application of the GT
workaround list and the steering isn't in place.  Let's add the same MCR
steering to the beginning of the RCS engine's workaround list to ensure
that it's always in place and we don't get erroneous messages about RCS
engine workarounds failing to apply.

References: https://gitlab.freedesktop.org/drm/intel/issues/1222
Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
Cc: chris at chris-wilson.co.uk
Signed-off-by: Matt Roper <matthew.d.roper at intel.com>
 drivers/gpu/drm/i915/gt/intel_workarounds.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/i915/gt/intel_workarounds.c b/drivers/gpu/drm/i915/gt/intel_workarounds.c
index 4a255de13394..b11b83546696 100644
--- a/drivers/gpu/drm/i915/gt/intel_workarounds.c
+++ b/drivers/gpu/drm/i915/gt/intel_workarounds.c
@@ -1345,6 +1345,9 @@ rcs_engine_wa_init(struct intel_engine_cs *engine, struct i915_wa_list *wal)
 	struct drm_i915_private *i915 = engine->i915;
+	if (INTEL_GEN(i915) >= 10)
+		wa_init_mcr(i915, wal);
 		 * Wa_1607138336:tgl

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