drm/i915: Move legacy kernel context pinning to intel_ringbuffer.c

This is so that we have symmetry with intel_lrc.c and avoid a source of
if (i915.enable_execlists) layering violation within i915_gem_context.c -
that is we move the specific handling of the dev_priv->kernel_context
for legacy submission into the legacy submission code.

This depends upon the init/fini ordering between contexts and engines
already defined by intel_lrc.c, and also exporting the context alignment
required for pinning the legacy context.

v2: Separate out pin/unpin context funcs for greater symmetry with
intel_lrc. One more step towards unifying behaviour between the two
classes of engines and towards fixing another bug in i915_switch_context
vs requests.

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/1466776558-21516-2-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_drv.h

@@ -872,6 +872,8 @@ struct i915_gem_context {
 	u32 user_handle;
 #define CONTEXT_NO_ZEROMAP		(1<<0)
 
+	u32 ggtt_alignment;
+
 	struct intel_context {
 		struct drm_i915_gem_object *state;
 		struct intel_ringbuffer *ringbuf;

drivers/gpu/drm/i915/i915_gem_context.c

@@ -268,6 +268,8 @@ __create_hw_context(struct drm_device *dev,
 	list_add_tail(&ctx->link, &dev_priv->context_list);
 	ctx->i915 = dev_priv;
 
+	ctx->ggtt_alignment = get_context_alignment(dev_priv);
+
 	if (dev_priv->hw_context_size) {
 		struct drm_i915_gem_object *obj =
 				i915_gem_alloc_context_obj(dev, dev_priv->hw_context_size);
@@ -451,26 +453,6 @@ int i915_gem_context_init(struct drm_device *dev)
 		return PTR_ERR(ctx);
 	}
 
-	if (!i915.enable_execlists && ctx->engine[RCS].state) {
-		int ret;
-
-		/* We may need to do things with the shrinker which
-		 * require us to immediately switch back to the default
-		 * context. This can cause a problem as pinning the
-		 * default context also requires GTT space which may not
-		 * be available. To avoid this we always pin the default
-		 * context.
-		 */
-		ret = i915_gem_obj_ggtt_pin(ctx->engine[RCS].state,
-					    get_context_alignment(dev_priv), 0);
-		if (ret) {
-			DRM_ERROR("Failed to pinned default global context (error %d)\n",
-				  ret);
-			i915_gem_context_unreference(ctx);
-			return ret;
-		}
-	}
-
 	dev_priv->kernel_context = ctx;
 
 	DRM_DEBUG_DRIVER("%s context support initialized\n",
@@ -507,9 +489,6 @@ void i915_gem_context_fini(struct drm_device *dev)
 
 	lockdep_assert_held(&dev->struct_mutex);
 
-	if (!i915.enable_execlists && dctx->engine[RCS].state)
-		i915_gem_object_ggtt_unpin(dctx->engine[RCS].state);
-
 	i915_gem_context_unreference(dctx);
 	dev_priv->kernel_context = NULL;
 
@@ -759,7 +738,7 @@ static int do_rcs_switch(struct drm_i915_gem_request *req)
 
 	/* Trying to pin first makes error handling easier. */
 	ret = i915_gem_obj_ggtt_pin(to->engine[RCS].state,
-				    get_context_alignment(engine->i915),
+				    to->ggtt_alignment,
 				    0);
 	if (ret)
 		return ret;

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -2321,6 +2321,47 @@ intel_ringbuffer_free(struct intel_ringbuffer *ring)
 	kfree(ring);
 }
 
+static int intel_ring_context_pin(struct i915_gem_context *ctx,
+				  struct intel_engine_cs *engine)
+{
+	struct intel_context *ce = &ctx->engine[engine->id];
+	int ret;
+
+	lockdep_assert_held(&ctx->i915->dev->struct_mutex);
+
+	if (ce->pin_count++)
+		return 0;
+
+	if (ce->state) {
+		ret = i915_gem_obj_ggtt_pin(ce->state, ctx->ggtt_alignment, 0);
+		if (ret)
+			goto error;
+	}
+
+	i915_gem_context_reference(ctx);
+	return 0;
+
+error:
+	ce->pin_count = 0;
+	return ret;
+}
+
+static void intel_ring_context_unpin(struct i915_gem_context *ctx,
+				     struct intel_engine_cs *engine)
+{
+	struct intel_context *ce = &ctx->engine[engine->id];
+
+	lockdep_assert_held(&ctx->i915->dev->struct_mutex);
+
+	if (--ce->pin_count)
+		return;
+
+	if (ce->state)
+		i915_gem_object_ggtt_unpin(ce->state);
+
+	i915_gem_context_unreference(ctx);
+}
+
 static int intel_init_ring_buffer(struct drm_device *dev,
 				  struct intel_engine_cs *engine)
 {
@@ -2341,6 +2382,17 @@ static int intel_init_ring_buffer(struct drm_device *dev,
 
 	init_waitqueue_head(&engine->irq_queue);
 
+	/* We may need to do things with the shrinker which
+	 * require us to immediately switch back to the default
+	 * context. This can cause a problem as pinning the
+	 * default context also requires GTT space which may not
+	 * be available. To avoid this we always pin the default
+	 * context.
+	 */
+	ret = intel_ring_context_pin(dev_priv->kernel_context, engine);
+	if (ret)
+		goto error;
+
 	ringbuf = intel_engine_create_ringbuffer(engine, 32 * PAGE_SIZE);
 	if (IS_ERR(ringbuf)) {
 		ret = PTR_ERR(ringbuf);
@@ -2408,6 +2460,9 @@ void intel_cleanup_engine(struct intel_engine_cs *engine)
 
 	i915_cmd_parser_fini_ring(engine);
 	i915_gem_batch_pool_fini(&engine->batch_pool);
+
+	intel_ring_context_unpin(dev_priv->kernel_context, engine);
+
 	engine->i915 = NULL;
 }