drm/i915/gen9: Add WaDisableGatherAtSetShaderCommonSlice

Add WaDisableGatherAtSetShaderCommonSlice for all gen9 as stated
by bspec. The bspec told to put this workaround to the per ctx bb.
Initial implementation and subsequent review were done based on
bspec. Arun raised a suspicion that this would belong to indirect bb
instead and he conducted more throughout investigation on the matter
and indeed the documentation was wrong.

v2: Move to indirect_ctx wa bb, as it is correct place (Arun)

References: HSD#2135817
Cc: Arun Siluvery <arun.siluvery@linux.intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com> (v1)
Reviewed-by: Arun Siluvery <arun.siluvery@linux.intel.com>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1469013973-24104-1-git-send-email-mika.kuoppala@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -6132,6 +6132,7 @@ enum {
 # define GEN7_CSC1_RHWO_OPT_DISABLE_IN_RCC	((1<<10) | (1<<26))
 # define GEN9_RHWO_OPTIMIZATION_DISABLE		(1<<14)
 #define COMMON_SLICE_CHICKEN2			_MMIO(0x7014)
+# define GEN9_DISABLE_GATHER_AT_SET_SHADER_COMMON_SLICE (1<<12)
 # define GEN8_SBE_DISABLE_REPLAY_BUF_OPTIMIZATION (1<<8)
 # define GEN8_CSC2_SBE_VUE_CACHE_CONSERVATIVE	(1<<0)
 

drivers/gpu/drm/i915/intel_lrc.c

@@ -1256,6 +1256,13 @@ static int gen9_init_indirectctx_bb(struct intel_engine_cs *engine,
 		return ret;
 	index = ret;
 
+	/* WaDisableGatherAtSetShaderCommonSlice:skl,bxt,kbl */
+	wa_ctx_emit(batch, index, MI_LOAD_REGISTER_IMM(1));
+	wa_ctx_emit_reg(batch, index, COMMON_SLICE_CHICKEN2);
+	wa_ctx_emit(batch, index, _MASKED_BIT_DISABLE(
+			    GEN9_DISABLE_GATHER_AT_SET_SHADER_COMMON_SLICE));
+	wa_ctx_emit(batch, index, MI_NOOP);
+
 	/* WaClearSlmSpaceAtContextSwitch:kbl */
 	/* Actual scratch location is at 128 bytes offset */
 	if (IS_KBL_REVID(engine->i915, 0, KBL_REVID_A0)) {