[PATCH 8/9] drm/i915: enable RC6 workaround on Haswell

[Eugeni Dodonov <eugeni.dodonov@intel.com>]

For Haswell, on some of the early hardware revisions, it is possible to
run into issues when RC6 state is enabled and when pipes change state.

v2: add comment saying that this is for early revisions only.

v3: beautify as suggested by Daniel Vetter.

Signed-off-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
---
 drivers/gpu/drm/i915/i915_reg.h |  5 +++++
 drivers/gpu/drm/i915/intel_pm.c | 10 ++++++++++
 2 files changed, 15 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 9d5bf06..793a172 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -4516,4 +4516,9 @@
 #define  SFUSE_STRAP_DDIC_DETECTED	(1<<1)
 #define  SFUSE_STRAP_DDID_DETECTED	(1<<0)
 
+#define WM_DBG				0x45280
+#define  WM_DBG_DISALLOW_MULTIPLE_LP	(1<<0)
+#define  WM_DBG_DISALLOW_MAXFIFO	(1<<1)
+#define  WM_DBG_DISALLOW_SPRITE		(1<<2)
+
 #endif /* _I915_REG_H_ */
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index bdcb5bd..2f6630a 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -3475,6 +3475,16 @@ static void haswell_init_clock_gating(struct drm_device *dev)
 	/* WaDisable4x2SubspanOptimization */
 	I915_WRITE(CACHE_MODE_1,
 		   _MASKED_BIT_ENABLE(PIXEL_SUBSPAN_COLLECT_OPT_DISABLE));
+
+	/* XXX: This is a workaround for early silicon revisions and should be
+	 * removed later.
+	 */
+	I915_WRITE(WM_DBG,
+			I915_READ(WM_DBG) |
+			WM_DBG_DISALLOW_MULTIPLE_LP |
+			WM_DBG_DISALLOW_SPRITE |
+			WM_DBG_DISALLOW_MAXFIFO);
+
 }
 
 static void ivybridge_init_clock_gating(struct drm_device *dev)
-- 
1.7.11.1