drm/i915/gen9: Add GEN8_CS_CHICKEN1 to HW whitelist

Required for WaEnablePreemptionGranularityControlByUMD:skl,bxt

This register is added to HW whitelist to support WA required for future
enabling of pre-emptive command execution, WA implementation will be in
userspace and it cannot program this register if it is not on HW whitelist.

v2: explain purpose of WA (Chris)
Reviewed-by: NNick Hoath <nicholas.hoath@intel.com>
Signed-off-by: NArun Siluvery <arun.siluvery@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1453412634-29238-3-git-send-email-arun.siluvery@linux.intel.comSigned-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -5998,6 +5998,8 @@ enum skl_disp_power_wells {
 #define FF_SLICE_CS_CHICKEN2			_MMIO(0x20e4)
 #define  GEN9_TSG_BARRIER_ACK_DISABLE		(1<<8)
 
+#define GEN8_CS_CHICKEN1		_MMIO(0x2580)
+
 /* GEN7 chicken */
 #define GEN7_COMMON_SLICE_CHICKEN1		_MMIO(0x7010)
 # define GEN7_CSC1_RHWO_OPT_DISABLE_IN_RCC	((1<<10) | (1<<26))

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -910,6 +910,7 @@ static int gen9_init_workarounds(struct intel_engine_cs *ring)
 	struct drm_device *dev = ring->dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	uint32_t tmp;
+	int ret;
 
 	/* WaEnableLbsSlaRetryTimerDecrement:skl */
 	I915_WRITE(BDW_SCRATCH1, I915_READ(BDW_SCRATCH1) |
@@ -980,6 +981,11 @@ static int gen9_init_workarounds(struct intel_engine_cs *ring)
 	/* WaDisableSTUnitPowerOptimization:skl,bxt */
 	WA_SET_BIT_MASKED(HALF_SLICE_CHICKEN2, GEN8_ST_PO_DISABLE);
 
+	/* WaEnablePreemptionGranularityControlByUMD:skl,bxt */
+	ret= wa_ring_whitelist_reg(ring, GEN8_CS_CHICKEN1);
+	if (ret)
+		return ret;
+
 	return 0;
 }