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

1 files changed, 13 insertions, 12 deletions

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 29b5afac7856..3ce1c87dec46 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/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);