drm/i915: Use engine->context_pin() to report the intel_ring

Since unifying ringbuffer/execlist submission to use
engine->pin_context, we ensure that the intel_ring is available before
we start constructing the request. We can therefore move the assignment
of the request->ring to the central i915_gem_request_alloc() and not
require it in every engine->request_alloc() callback. Another small step
towards simplification (of the core, but at a cost of handling error
pointers in less important callers of engine->pin_context).

v2: Rearrange a few branches to reduce impact of PTR_ERR() on gcc's code
generation.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Oscar Mateo <oscar.mateo@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Oscar Mateo <oscar.mateo@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170504093308.4137-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gvt/scheduler.c

@@ -180,6 +180,7 @@ static int dispatch_workload(struct intel_vgpu_workload *workload)
 	struct intel_engine_cs *engine = dev_priv->engine[ring_id];
 	struct drm_i915_gem_request *rq;
 	struct intel_vgpu *vgpu = workload->vgpu;
+	struct intel_ring *ring;
 	int ret;
 
 	gvt_dbg_sched("ring id %d prepare to dispatch workload %p\n",
@@ -198,8 +199,9 @@ static int dispatch_workload(struct intel_vgpu_workload *workload)
 	 * shadow_ctx pages invalid. So gvt need to pin itself. After update
 	 * the guest context, gvt can unpin the shadow_ctx safely.
 	 */
-	ret = engine->context_pin(engine, shadow_ctx);
-	if (ret) {
+	ring = engine->context_pin(engine, shadow_ctx);
+	if (IS_ERR(ring)) {
+		ret = PTR_ERR(ring);
 		gvt_vgpu_err("fail to pin shadow context\n");
 		workload->status = ret;
 		mutex_unlock(&dev_priv->drm.struct_mutex);

drivers/gpu/drm/i915/i915_gem_request.c

@@ -551,6 +551,7 @@ i915_gem_request_alloc(struct intel_engine_cs *engine,
 {
 	struct drm_i915_private *dev_priv = engine->i915;
 	struct drm_i915_gem_request *req;
+	struct intel_ring *ring;
 	int ret;
 
 	lockdep_assert_held(&dev_priv->drm.struct_mutex);
@@ -565,9 +566,10 @@ i915_gem_request_alloc(struct intel_engine_cs *engine,
 	 * GGTT space, so do this first before we reserve a seqno for
 	 * ourselves.
 	 */
-	ret = engine->context_pin(engine, ctx);
-	if (ret)
-		return ERR_PTR(ret);
+	ring = engine->context_pin(engine, ctx);
+	if (IS_ERR(ring))
+		return ERR_CAST(ring);
+	GEM_BUG_ON(!ring);
 
 	ret = reserve_seqno(engine);
 	if (ret)
@@ -633,6 +635,7 @@ i915_gem_request_alloc(struct intel_engine_cs *engine,
 	req->i915 = dev_priv;
 	req->engine = engine;
 	req->ctx = ctx;
+	req->ring = ring;
 
 	/* No zalloc, must clear what we need by hand */
 	req->global_seqno = 0;

drivers/gpu/drm/i915/i915_perf.c

@@ -744,6 +744,7 @@ static int oa_get_render_ctx_id(struct i915_perf_stream *stream)
 {
 	struct drm_i915_private *dev_priv = stream->dev_priv;
 	struct intel_engine_cs *engine = dev_priv->engine[RCS];
+	struct intel_ring *ring;
 	int ret;
 
 	ret = i915_mutex_lock_interruptible(&dev_priv->drm);
@@ -755,9 +756,10 @@ static int oa_get_render_ctx_id(struct i915_perf_stream *stream)
 	 *
 	 * NB: implied RCS engine...
 	 */
-	ret = engine->context_pin(engine, stream->ctx);
-	if (ret)
-		goto unlock;
+	ring = engine->context_pin(engine, stream->ctx);
+	mutex_unlock(&dev_priv->drm.struct_mutex);
+	if (IS_ERR(ring))
+		return PTR_ERR(ring);
 
 	/* Explicitly track the ID (instead of calling i915_ggtt_offset()
 	 * on the fly) considering the difference with gen8+ and
@@ -766,10 +768,7 @@ static int oa_get_render_ctx_id(struct i915_perf_stream *stream)
 	dev_priv->perf.oa.specific_ctx_id =
 		i915_ggtt_offset(stream->ctx->engine[engine->id].state);
 
-unlock:
-	mutex_unlock(&dev_priv->drm.struct_mutex);
-
-	return ret;
+	return 0;
 }
 
 /**

drivers/gpu/drm/i915/intel_engine_cs.c

@@ -469,6 +469,7 @@ static void intel_engine_cleanup_scratch(struct intel_engine_cs *engine)
  */
 int intel_engine_init_common(struct intel_engine_cs *engine)
 {
+	struct intel_ring *ring;
 	int ret;
 
 	engine->set_default_submission(engine);
@@ -480,9 +481,9 @@ int intel_engine_init_common(struct intel_engine_cs *engine)
 	 * be available. To avoid this we always pin the default
 	 * context.
 	 */
-	ret = engine->context_pin(engine, engine->i915->kernel_context);
-	if (ret)
-		return ret;
+	ring = engine->context_pin(engine, engine->i915->kernel_context);
+	if (IS_ERR(ring))
+		return PTR_ERR(ring);
 
 	ret = intel_engine_init_breadcrumbs(engine);
 	if (ret)

drivers/gpu/drm/i915/intel_lrc.c

@@ -740,8 +740,9 @@ static void execlists_schedule(struct drm_i915_gem_request *request, int prio)
 	/* XXX Do we need to preempt to make room for us and our deps? */
 }
 
-static int execlists_context_pin(struct intel_engine_cs *engine,
-				 struct i915_gem_context *ctx)
+static struct intel_ring *
+execlists_context_pin(struct intel_engine_cs *engine,
+		      struct i915_gem_context *ctx)
 {
 	struct intel_context *ce = &ctx->engine[engine->id];
 	unsigned int flags;
@@ -750,8 +751,8 @@ static int execlists_context_pin(struct intel_engine_cs *engine,
 
 	lockdep_assert_held(&ctx->i915->drm.struct_mutex);
 
-	if (ce->pin_count++)
-		return 0;
+	if (likely(ce->pin_count++))
+		goto out;
 	GEM_BUG_ON(!ce->pin_count); /* no overflow please! */
 
 	if (!ce->state) {
@@ -788,7 +789,8 @@ static int execlists_context_pin(struct intel_engine_cs *engine,
 	ce->state->obj->mm.dirty = true;
 
 	i915_gem_context_get(ctx);
-	return 0;
+out:
+	return ce->ring;
 
 unpin_map:
 	i915_gem_object_unpin_map(ce->state->obj);
@@ -796,7 +798,7 @@ static int execlists_context_pin(struct intel_engine_cs *engine,
 	__i915_vma_unpin(ce->state);
 err:
 	ce->pin_count = 0;
-	return ret;
+	return ERR_PTR(ret);
 }
 
 static void execlists_context_unpin(struct intel_engine_cs *engine,
@@ -833,9 +835,6 @@ static int execlists_request_alloc(struct drm_i915_gem_request *request)
 	 */
 	request->reserved_space += EXECLISTS_REQUEST_SIZE;
 
-	GEM_BUG_ON(!ce->ring);
-	request->ring = ce->ring;
-
 	if (i915.enable_guc_submission) {
 		/*
 		 * Check that the GuC has space for the request before

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -1475,16 +1475,17 @@ alloc_context_vma(struct intel_engine_cs *engine)
 	return vma;
 }
 
-static int intel_ring_context_pin(struct intel_engine_cs *engine,
-				  struct i915_gem_context *ctx)
+static struct intel_ring *
+intel_ring_context_pin(struct intel_engine_cs *engine,
+		       struct i915_gem_context *ctx)
 {
 	struct intel_context *ce = &ctx->engine[engine->id];
 	int ret;
 
 	lockdep_assert_held(&ctx->i915->drm.struct_mutex);
 
-	if (ce->pin_count++)
-		return 0;
+	if (likely(ce->pin_count++))
+		goto out;
 	GEM_BUG_ON(!ce->pin_count); /* no overflow please! */
 
 	if (!ce->state && engine->context_size) {
@@ -1493,7 +1494,7 @@ static int intel_ring_context_pin(struct intel_engine_cs *engine,
 		vma = alloc_context_vma(engine);
 		if (IS_ERR(vma)) {
 			ret = PTR_ERR(vma);
-			goto error;
+			goto err;
 		}
 
 		ce->state = vma;
@@ -1502,7 +1503,7 @@ static int intel_ring_context_pin(struct intel_engine_cs *engine,
 	if (ce->state) {
 		ret = context_pin(ctx);
 		if (ret)
-			goto error;
+			goto err;
 
 		ce->state->obj->mm.dirty = true;
 	}
@@ -1518,11 +1519,14 @@ static int intel_ring_context_pin(struct intel_engine_cs *engine,
 		ce->initialised = true;
 
 	i915_gem_context_get(ctx);
-	return 0;
 
-error:
+out:
+	/* One ringbuffer to rule them all */
+	return engine->buffer;
+
+err:
 	ce->pin_count = 0;
-	return ret;
+	return ERR_PTR(ret);
 }
 
 static void intel_ring_context_unpin(struct intel_engine_cs *engine,
@@ -1634,9 +1638,6 @@ static int ring_request_alloc(struct drm_i915_gem_request *request)
 	 */
 	request->reserved_space += LEGACY_REQUEST_SIZE;
 
-	GEM_BUG_ON(!request->engine->buffer);
-	request->ring = request->engine->buffer;
-
 	cs = intel_ring_begin(request, 0);
 	if (IS_ERR(cs))
 		return PTR_ERR(cs);

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -271,8 +271,8 @@ struct intel_engine_cs {
 
 	void		(*set_default_submission)(struct intel_engine_cs *engine);
 
-	int		(*context_pin)(struct intel_engine_cs *engine,
-				       struct i915_gem_context *ctx);
+	struct intel_ring *(*context_pin)(struct intel_engine_cs *engine,
+					  struct i915_gem_context *ctx);
 	void		(*context_unpin)(struct intel_engine_cs *engine,
 					 struct i915_gem_context *ctx);
 	int		(*request_alloc)(struct drm_i915_gem_request *req);

drivers/gpu/drm/i915/selftests/mock_engine.c

@@ -52,11 +52,12 @@ static void hw_delay_complete(unsigned long data)
 	spin_unlock(&engine->hw_lock);
 }
 
-static int mock_context_pin(struct intel_engine_cs *engine,
-			    struct i915_gem_context *ctx)
+static struct intel_ring *
+mock_context_pin(struct intel_engine_cs *engine,
+		 struct i915_gem_context *ctx)
 {
 	i915_gem_context_get(ctx);
-	return 0;
+	return engine->buffer;
 }
 
 static void mock_context_unpin(struct intel_engine_cs *engine,
@@ -72,7 +73,6 @@ static int mock_request_alloc(struct drm_i915_gem_request *request)
 	INIT_LIST_HEAD(&mock->link);
 	mock->delay = 0;
 
-	request->ring = request->engine->buffer;
 	return 0;
 }