[PATCH 17/59] drm/i915: Implement ReadHitWriteOnlyDisable.

[Timo Aaltonen]

From: Rafael Antognolli <rafael.antognolli at intel.com>

BugLink: http://bugs.launchpad.net/bugs/1757573

The workaround for this is described as:

"if RenderSurfaceState.Num_Multisamples > 1, disable RCC clock gating if
RenderSurfaceState.Num_Multisamples == 1, set 0x7010[14] = 1"

Further documentation in the internal bug referenced by the bspec
suggest that any of the above suggestions should suffice to fix the
issue. We are going with disabling RCC clock gating.

Unfortunately, what we are doing doesn't match the name of the
workaround, but at least it matches its description.

This change improves CNL stability by avoiding some of the hangs seen in
the platform.

v2: Only disable RCC clock gating.

Signed-off-by: Rafael Antognolli <rafael.antognolli at intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171103183027.5051-1-rafael.antognolli@intel.com
(cherry picked from commit 0a60797a0efbc495f514304d83eb289bb55990a6)
Signed-off-by: Timo Aaltonen <timo.aaltonen at canonical.com>
---
 drivers/gpu/drm/i915/i915_reg.h        | 1 +
 drivers/gpu/drm/i915/intel_engine_cs.c | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 57ed23091c3c..f7fb79d7b4a3 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -3834,6 +3834,7 @@ enum {
  */
 #define SLICE_UNIT_LEVEL_CLKGATE	_MMIO(0x94d4)
 #define  SARBUNIT_CLKGATE_DIS		(1 << 5)
+#define  RCCUNIT_CLKGATE_DIS		(1 << 7)
 
 /*
  * Display engine regs
diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
index 6074e04dc99f..f2736474f6a1 100644
--- a/drivers/gpu/drm/i915/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/intel_engine_cs.c
@@ -1320,6 +1320,9 @@ static int cnl_init_workarounds(struct intel_engine_cs *engine)
 	WA_SET_FIELD_MASKED(GEN8_CS_CHICKEN1, GEN9_PREEMPT_GPGPU_LEVEL_MASK,
 			    GEN9_PREEMPT_GPGPU_COMMAND_LEVEL);
 
+	/* ReadHitWriteOnlyDisable: cnl */
+	WA_SET_BIT_MASKED(SLICE_UNIT_LEVEL_CLKGATE, RCCUNIT_CLKGATE_DIS);
+
 	/* WaEnablePreemptionGranularityControlByUMD:cnl */
 	I915_WRITE(GEN7_FF_SLICE_CS_CHICKEN1,
 		   _MASKED_BIT_ENABLE(GEN9_FFSC_PERCTX_PREEMPT_CTRL));
-- 
2.15.1