drm/i915/skl: Implement WaEnableLbsSlaRetryTimerDecrement

This W/A is put in a gen9 specific function because it may well be
needed on other gen9 platforms.
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Nick Hoath <nicholas.hoath@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -5285,6 +5285,9 @@ enum skl_disp_power_wells {
 #define HSW_SCRATCH1				0xb038
 #define  HSW_SCRATCH1_L3_DATA_ATOMICS_DISABLE	(1<<27)
 
+#define BDW_SCRATCH1					0xb11c
+#define  GEN9_LBS_SLA_RETRY_TIMER_DECREMENT_ENABLE	(1<<2)
+
 /* PCH */
 
 /* south display engine interrupt: IBX */

drivers/gpu/drm/i915/intel_pm.c

@@ -52,10 +52,21 @@
 #define INTEL_RC6p_ENABLE			(1<<1)
 #define INTEL_RC6pp_ENABLE			(1<<2)
 
+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) |
+		   GEN9_LBS_SLA_RETRY_TIMER_DECREMENT_ENABLE);
+}
+
 static void skl_init_clock_gating(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 
+	gen9_init_clock_gating(dev);
+
 	if (INTEL_REVID(dev) == SKL_REVID_A0) {
 		/*
 		 * WaDisableSDEUnitClockGating:skl