drm/i915: Only change the context object's domain when binding

We know that the only access to the context object is via the GPU, and
the only time when it can be out of the GPU domain is when it is swapped
out and unbound. Therefore we only need to clflush the object when
binding, thus avoiding any potential stall on touching the domain on an
active context.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1471254551-25805-16-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_context.c

@@ -772,6 +772,13 @@ static int do_rcs_switch(struct drm_i915_gem_request *req)
 	if (skip_rcs_switch(ppgtt, engine, to))
 		return 0;
 
+	/* Clear this page out of any CPU caches for coherent swap-in/out. */
+	if (!(vma->flags & I915_VMA_GLOBAL_BIND)) {
+		ret = i915_gem_object_set_to_gtt_domain(vma->obj, false);
+		if (ret)
+			return ret;
+	}
+
 	/* Trying to pin first makes error handling easier. */
 	ret = i915_vma_pin(vma, 0, to->ggtt_alignment, PIN_GLOBAL);
 	if (ret)
@@ -786,18 +793,6 @@ static int do_rcs_switch(struct drm_i915_gem_request *req)
 	 */
 	from = engine->last_context;
 
-	/*
-	 * Clear this page out of any CPU caches for coherent swap-in/out. Note
-	 * that thanks to write = false in this call and us not setting any gpu
-	 * write domains when putting a context object onto the active list
-	 * (when switching away from it), this won't block.
-	 *
-	 * XXX: We need a real interface to do this instead of trickery.
-	 */
-	ret = i915_gem_object_set_to_gtt_domain(vma->obj, false);
-	if (ret)
-		goto err;
-
 	if (needs_pd_load_pre(ppgtt, engine, to)) {
 		/* Older GENs and non render rings still want the load first,
 		 * "PP_DCLV followed by PP_DIR_BASE register through Load

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -2092,6 +2092,10 @@ static int intel_ring_context_pin(struct i915_gem_context *ctx,
 		return 0;
 
 	if (ce->state) {
+		ret = i915_gem_object_set_to_gtt_domain(ce->state->obj, false);
+		if (ret)
+			goto error;
+
 		ret = i915_vma_pin(ce->state, 0, ctx->ggtt_alignment,
 				   PIN_GLOBAL | PIN_HIGH);
 		if (ret)