[Intel-gfx] [PATCH v3] 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.

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.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_drv.h         | 6 ++++++
 drivers/gpu/drm/i915/i915_gem.c         | 2 ++
 drivers/gpu/drm/i915/i915_perf.c        | 4 +++-
 drivers/gpu/drm/i915/intel_lrc.c        | 8 +++++---
 drivers/gpu/drm/i915/intel_ringbuffer.c | 2 +-
 5 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 7ea442033a57..5c833a45682d 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3074,6 +3074,12 @@ 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/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 89834ce19acd..d6f2bbd6a0dc 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -5417,6 +5417,8 @@ static int __intel_engines_record_defaults(struct drm_i915_private *i915)
 	for_each_engine(engine, i915, id) {
 		struct i915_vma *state;
 
+		GEM_BUG_ON(to_intel_context(ctx, engine)->pin_count);
+
 		state = to_intel_context(ctx, engine)->state;
 		if (!state)
 			continue;
diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
index 3d7a052b4cca..90168ac845c2 100644
--- a/drivers/gpu/drm/i915/i915_perf.c
+++ b/drivers/gpu/drm/i915/i915_perf.c
@@ -1735,13 +1735,15 @@ static int gen8_configure_all_contexts(struct drm_i915_private *dev_priv,
 	/* Update all contexts now that we've stalled the submission. */
 	list_for_each_entry(ctx, &dev_priv->contexts.list, link) {
 		struct intel_context *ce = to_intel_context(ctx, engine);
+		unsigned int map_type;
 		u32 *regs;
 
 		/* OA settings will be set upon first use */
 		if (!ce->state)
 			continue;
 
-		regs = i915_gem_object_pin_map(ce->state->obj, I915_MAP_WB);
+		map_type = i915_coherent_map_type(dev_priv);
+		regs = i915_gem_object_pin_map(ce->state->obj, map_type);
 		if (IS_ERR(regs))
 			return PTR_ERR(regs);
 
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index d7fcbba8e982..7b1f322f232b 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/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;
@@ -2753,7 +2755,7 @@ populate_lr_context(struct i915_gem_context *ctx,
 		void *defaults;
 
 		defaults = i915_gem_object_pin_map(engine->default_state,
-						   I915_MAP_WB);
+						   I915_MAP_FORCE_WB);
 		if (IS_ERR(defaults)) {
 			ret = PTR_ERR(defaults);
 			goto err_unpin_ctx;
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index d0ef50bf930a..1eb68d77b66c 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -1288,7 +1288,7 @@ alloc_context_vma(struct intel_engine_cs *engine)
 		}
 
 		defaults = i915_gem_object_pin_map(engine->default_state,
-						   I915_MAP_WB);
+						   I915_MAP_FORCE_WB);
 		if (IS_ERR(defaults)) {
 			err = PTR_ERR(defaults);
 			goto err_map;
-- 
2.19.0