drm/i915/gen9: Add WaVFEStateAfterPipeControlwithMediaStateClear

Kernel only need to add a register to HW whitelist, required for a
preemption related issue.

Reference: HSD#2131039
Reviewed-by: NJeff McGee <jeff.mcgee@intel.com>
Signed-off-by: NArun Siluvery <arun.siluvery@linux.intel.com>
Signed-off-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1465203169-16591-1-git-send-email-arun.siluvery@linux.intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -6072,6 +6072,7 @@ enum skl_disp_power_wells {
 #define  GEN9_TSG_BARRIER_ACK_DISABLE		(1<<8)
 
 #define GEN9_CS_DEBUG_MODE1		_MMIO(0x20ec)
+#define GEN9_CTX_PREEMPT_REG		_MMIO(0x2248)
 #define GEN8_CS_CHICKEN1		_MMIO(0x2580)
 
 /* GEN7 chicken */

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -987,6 +987,11 @@ static int gen9_init_workarounds(struct intel_engine_cs *engine)
 	I915_WRITE(GEN8_L3SQCREG4, (I915_READ(GEN8_L3SQCREG4) |
 				    GEN8_LQSC_FLUSH_COHERENT_LINES));
 
+	/* WaVFEStateAfterPipeControlwithMediaStateClear:skl,bxt */
+	ret = wa_ring_whitelist_reg(engine, GEN9_CTX_PREEMPT_REG);
+	if (ret)
+		return ret;
+
 	/* WaEnablePreemptionGranularityControlByUMD:skl,bxt */
 	ret= wa_ring_whitelist_reg(engine, GEN8_CS_CHICKEN1);
 	if (ret)