[PATCH 11/21] drm/i915: disable GTT cache for 2M pages

[Matthew Auld]

When SW enables the use of 2M/1G pages, it must disable the GTT cache.

v2: don't disable for Cherryview which doesn't even support 48b PPGTT!

v3: explicitly check that the system does support 2M/1G pages

v4: split WA and decision logic

Signed-off-by: Matthew Auld <matthew.auld at intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
---
 drivers/gpu/drm/i915/intel_pm.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 171b21f6c4ad..8752954c5920 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -8454,6 +8454,8 @@ static void skl_init_clock_gating(struct drm_i915_private *dev_priv)
 static void bdw_init_clock_gating(struct drm_i915_private *dev_priv)
 {
 	enum pipe pipe;
+	bool can_use_gtt_cache = !HAS_PAGE_SIZES(dev_priv,
+						 I915_GTT_PAGE_SIZE_2M);
 
 	ilk_init_lp_watermarks(dev_priv);
 
@@ -8489,10 +8491,9 @@ static void bdw_init_clock_gating(struct drm_i915_private *dev_priv)
 
 	/*
 	 * WaGttCachingOffByDefault:bdw
-	 * GTT cache may not work with big pages, so if those
-	 * are ever enabled GTT cache may need to be disabled.
+	 * The GTT cache must be disabled if the system is using 2M pages.
 	 */
-	I915_WRITE(HSW_GTT_CACHE_EN, GTT_CACHE_EN_ALL);
+	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)
-- 
2.13.5