[Intel-gfx] [PATCH] drm/i915: RMW register cycles considered evil

[Daniel Vetter]

Especially for workarounds which is stuff that's almost impossible to
verify: The initial state from the firmware on boot-up and after
resume could be different, which will hide bugs when we do an RMW
cycle.

Hence never do them, and if it's required we need a special mask.

Cc: Damien Lespiau <damien.lespiau at intel.com>
Cc: Imre Deak <imre.deak at intel.com>
Cc: Nick Hoath <nicholas.hoath at intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
---
 drivers/gpu/drm/i915/intel_pm.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 166ae51f5a5b..565f78d6a21d 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -57,7 +57,7 @@ static void gen9_init_clock_gating(struct drm_device *dev)
 	struct drm_i915_private *dev_priv = dev->dev_private;
 
 	/* WaEnableLbsSlaRetryTimerDecrement:skl */
-	I915_WRITE(BDW_SCRATCH1, I915_READ(BDW_SCRATCH1) |
+	I915_WRITE(BDW_SCRATCH1,
 		   GEN9_LBS_SLA_RETRY_TIMER_DECREMENT_ENABLE);
 }
 
@@ -72,18 +72,18 @@ static void skl_init_clock_gating(struct drm_device *dev)
 		 * WaDisableSDEUnitClockGating:skl
 		 * WaSetGAPSunitClckGateDisable:skl
 		 */
-		I915_WRITE(GEN8_UCGCTL6, I915_READ(GEN8_UCGCTL6) |
+		I915_WRITE(GEN8_UCGCTL6,
 			   GEN8_GAPSUNIT_CLOCK_GATE_DISABLE |
 			   GEN8_SDEUNIT_CLOCK_GATE_DISABLE);
 
 		/* WaDisableVFUnitClockGating:skl */
-		I915_WRITE(GEN6_UCGCTL2, I915_READ(GEN6_UCGCTL2) |
+		I915_WRITE(GEN6_UCGCTL2,
 			   GEN6_VFUNIT_CLOCK_GATE_DISABLE);
 	}
 
 	if (INTEL_REVID(dev) <= SKL_REVID_D0) {
 		/* WaDisableHDCInvalidation:skl */
-		I915_WRITE(GAM_ECOCHK, I915_READ(GAM_ECOCHK) |
+		I915_WRITE(GAM_ECOCHK,
 			   BDW_DISABLE_HDC_INVALIDATION);
 
 		/* WaDisableChickenBitTSGBarrierAckForFFSliceCS:skl */
@@ -93,7 +93,7 @@ static void skl_init_clock_gating(struct drm_device *dev)
 
 	if (INTEL_REVID(dev) <= SKL_REVID_E0)
 		/* WaDisableLSQCROPERFforOCL:skl */
-		I915_WRITE(GEN8_L3SQCREG4, I915_READ(GEN8_L3SQCREG4) |
+		I915_WRITE(GEN8_L3SQCREG4,
 			   GEN8_LQSC_RO_PERF_DIS);
 }
 
@@ -109,12 +109,12 @@ static void bxt_init_clock_gating(struct drm_device *dev)
 	 * GEN8_HDCUNIT_CLOCK_GATE_DISABLE_HDCREQ applies on 3x6 GT SKUs only.
 	 */
 	 /* WaDisableSDEUnitClockGating:bxt */
-	I915_WRITE(GEN8_UCGCTL6, I915_READ(GEN8_UCGCTL6) |
+	I915_WRITE(GEN8_UCGCTL6,
 		   GEN8_SDEUNIT_CLOCK_GATE_DISABLE |
 		   GEN8_HDCUNIT_CLOCK_GATE_DISABLE_HDCREQ);
 
 	/* FIXME: apply on A0 only */
-	I915_WRITE(TILECTL, I915_READ(TILECTL) | TILECTL_TLBPF);
+	I915_WRITE(TILECTL, TILECTL_TLBPF);
 }
 
 static void i915_pineview_get_mem_freq(struct drm_device *dev)
-- 
2.1.4