drm/i915/execlists: Use coherent writes into the context image

That we use a WB mapping for updating the RING_TAIL register inside the
context image even on !llc machines has been a source of consternation
for every reader. It appears to work on bsw+, but it may just have been
that we have been incredibly bad at detecting the errors.

v2: With extra enthusiasm.
v3: Drop force of map type for pinned default_state as by the time we
pin it, the map type is always WB and doesn't conflict with the earlier
use by ce->state.
v4: Transfer engine->default_state from MAP_WC to MAP_WB on creation so
we do not need the MAP_FORCE littered around the backends
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180914123504.2062-3-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_drv.h

@@ -3096,6 +3096,12 @@ enum i915_map_type {
 	I915_MAP_FORCE_WC = I915_MAP_WC | I915_MAP_OVERRIDE,
 };
 
+static inline enum i915_map_type
+i915_coherent_map_type(struct drm_i915_private *i915)
+{
+	return HAS_LLC(i915) ? I915_MAP_WB : I915_MAP_WC;
+}
+
 /**
  * i915_gem_object_pin_map - return a contiguous mapping of the entire object
  * @obj: the object to map into kernel address space

drivers/gpu/drm/i915/i915_gem.c

@@ -5418,6 +5418,8 @@ static int __intel_engines_record_defaults(struct drm_i915_private *i915)
 		struct i915_vma *state;
 		void *vaddr;
 
+		GEM_BUG_ON(to_intel_context(ctx, engine)->pin_count);
+
 		state = to_intel_context(ctx, engine)->state;
 		if (!state)
 			continue;
@@ -5442,7 +5444,7 @@ static int __intel_engines_record_defaults(struct drm_i915_private *i915)
 
 		/* Check we can acquire the image of the context state */
 		vaddr = i915_gem_object_pin_map(engine->default_state,
-						I915_MAP_WB);
+						I915_MAP_FORCE_WB);
 		if (IS_ERR(vaddr)) {
 			err = PTR_ERR(vaddr);
 			goto err_active;

drivers/gpu/drm/i915/i915_perf.c

@@ -1707,6 +1707,7 @@ static int gen8_configure_all_contexts(struct drm_i915_private *dev_priv,
 				       const struct i915_oa_config *oa_config)
 {
 	struct intel_engine_cs *engine = dev_priv->engine[RCS];
+	unsigned int map_type = i915_coherent_map_type(dev_priv);
 	struct i915_gem_context *ctx;
 	struct i915_request *rq;
 	int ret;
@@ -1741,7 +1742,7 @@ static int gen8_configure_all_contexts(struct drm_i915_private *dev_priv,
 		if (!ce->state)
 			continue;
 
-		regs = i915_gem_object_pin_map(ce->state->obj, I915_MAP_WB);
+		regs = i915_gem_object_pin_map(ce->state->obj, map_type);
 		if (IS_ERR(regs))
 			return PTR_ERR(regs);
 

drivers/gpu/drm/i915/intel_lrc.c

@@ -1294,7 +1294,7 @@ static int __context_pin(struct i915_gem_context *ctx, struct i915_vma *vma)
 	 * on an active context (which by nature is already on the GPU).
 	 */
 	if (!(vma->flags & I915_VMA_GLOBAL_BIND)) {
-		err = i915_gem_object_set_to_gtt_domain(vma->obj, true);
+		err = i915_gem_object_set_to_wc_domain(vma->obj, true);
 		if (err)
 			return err;
 	}
@@ -1322,7 +1322,9 @@ __execlists_context_pin(struct intel_engine_cs *engine,
 	if (ret)
 		goto err;
 
-	vaddr = i915_gem_object_pin_map(ce->state->obj, I915_MAP_WB);
+	vaddr = i915_gem_object_pin_map(ce->state->obj,
+					i915_coherent_map_type(ctx->i915) |
+					I915_MAP_OVERRIDE);
 	if (IS_ERR(vaddr)) {
 		ret = PTR_ERR(vaddr);
 		goto unpin_vma;