[Intel-gfx] [PATCH 2/2] drm/i915/execlists: Use coherent writes into the context image

[Chris Wilson]

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.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_drv.h  | 6 ++++++
 drivers/gpu/drm/i915/intel_lrc.c | 5 +++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 5fa13887b911..8abd96c0ba79 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3069,6 +3069,12 @@ 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
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 3632521a5fb2..2c36c5befe5f 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1292,7 +1292,7 @@ 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;
 	}
@@ -1320,7 +1320,8 @@ __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));
 	if (IS_ERR(vaddr)) {
 		ret = PTR_ERR(vaddr);
 		goto unpin_vma;
-- 
2.18.0