[PATCH 1/2] drm/i915: enable the GTT cache

[Matthew Auld]

With 2M pages and the GTT cache enabled we know that something is busted
on BDW at least, however there's no evidence to suggest the same for
other platforms.

Signed-off-by: Matthew Auld <matthew.auld at intel.com>
---
 drivers/gpu/drm/i915/i915_gem_gtt.c | 12 ++++++++++++
 drivers/gpu/drm/i915/intel_pm.c     | 12 ------------
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index 5e7efbbac9f7..c550f30f7fd5 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -2153,6 +2153,18 @@ static void gtt_write_workarounds(struct drm_i915_private *dev_priv)
 		I915_WRITE(GEN8_GAMW_ECO_DEV_RW_IA,
 			   I915_READ(GEN8_GAMW_ECO_DEV_RW_IA) |
 			   GAMW_ECO_ENABLE_64K_IPS_FIELD);
+
+	if (INTEL_GEN(dev_priv) >= 8) {
+		bool can_use_gtt_cache = true;
+
+		if (HAS_PAGE_SIZES(dev_priv, I915_GTT_PAGE_SIZE_2M) &&
+		    IS_BROADWELL(dev_priv))
+			can_use_gtt_cache = false;
+
+		/* WaGttCachingOffByDefault */
+		I915_WRITE(HSW_GTT_CACHE_EN, can_use_gtt_cache ? GTT_CACHE_EN_ALL : 0);
+		WARN_ON_ONCE(can_use_gtt_cache && I915_READ(HSW_GTT_CACHE_EN) == 0);
+	}
 }
 
 int i915_ppgtt_init_hw(struct drm_i915_private *dev_priv)
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index ea187c182383..919632e09ad8 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -8493,9 +8493,6 @@ static void skl_init_clock_gating(struct drm_i915_private *dev_priv)
 
 static void bdw_init_clock_gating(struct drm_i915_private *dev_priv)
 {
-	/* The GTT cache must be disabled if the system is using 2M pages. */
-	bool can_use_gtt_cache = !HAS_PAGE_SIZES(dev_priv,
-						 I915_GTT_PAGE_SIZE_2M);
 	enum pipe pipe;
 
 	/* WaSwitchSolVfFArbitrationPriority:bdw */
@@ -8528,9 +8525,6 @@ static void bdw_init_clock_gating(struct drm_i915_private *dev_priv)
 	/* WaProgramL3SqcReg1Default:bdw */
 	gen8_set_l3sqc_credits(dev_priv, 30, 2);
 
-	/* WaGttCachingOffByDefault:bdw */
-	I915_WRITE(HSW_GTT_CACHE_EN, can_use_gtt_cache ? GTT_CACHE_EN_ALL : 0);
-
 	/* WaKVMNotificationOnConfigChange:bdw */
 	I915_WRITE(CHICKEN_PAR2_1, I915_READ(CHICKEN_PAR2_1)
 		   | KVM_CONFIG_CHANGE_NOTIFICATION_SELECT);
@@ -8795,12 +8789,6 @@ static void chv_init_clock_gating(struct drm_i915_private *dev_priv)
 	 * LSQC Setting Recommendations.
 	 */
 	gen8_set_l3sqc_credits(dev_priv, 38, 2);
-
-	/*
-	 * GTT cache may not work with big pages, so if those
-	 * are ever enabled GTT cache may need to be disabled.
-	 */
-	I915_WRITE(HSW_GTT_CACHE_EN, GTT_CACHE_EN_ALL);
 }
 
 static void g4x_init_clock_gating(struct drm_i915_private *dev_priv)
-- 
2.14.3