drm/i915/ringbuffer: Make context pin/unpin symmetric

Currently, we have a special routine for pinning the context state at
the start of activity tracking, but lack the complementary unpin
routine. Create it to to ease later patches that want to do partial
teardown on error, and, not least, to improve the readability of the
code.

Suggested-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Matthew Auld <matthew.william.auld@gmail.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180605085348.3018-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -1193,20 +1193,14 @@ static void intel_ring_context_destroy(struct intel_context *ce)
 		__i915_gem_object_release_unless_active(ce->state->obj);
 }
 
-static void intel_ring_context_unpin(struct intel_context *ce)
-{
-	if (ce->state) {
-		ce->state->obj->pin_global--;
-		i915_vma_unpin(ce->state);
-	}
-
-	i915_gem_context_put(ce->gem_context);
-}
-
 static int __context_pin(struct intel_context *ce)
 {
-	struct i915_vma *vma = ce->state;
-	int ret;
+	struct i915_vma *vma;
+	int err;
+
+	vma = ce->state;
+	if (!vma)
+		return 0;
 
 	/*
 	 * Clear this page out of any CPU caches for coherent swap-in/out.
@@ -1214,13 +1208,42 @@ static int __context_pin(struct intel_context *ce)
 	 * on an active context (which by nature is already on the GPU).
 	 */
 	if (!(vma->flags & I915_VMA_GLOBAL_BIND)) {
-		ret = i915_gem_object_set_to_gtt_domain(vma->obj, true);
-		if (ret)
-			return ret;
+		err = i915_gem_object_set_to_gtt_domain(vma->obj, true);
+		if (err)
+			return err;
 	}
 
-	return i915_vma_pin(vma, 0, I915_GTT_MIN_ALIGNMENT,
-			    PIN_GLOBAL | PIN_HIGH);
+	err = i915_vma_pin(vma, 0, I915_GTT_MIN_ALIGNMENT,
+			   PIN_GLOBAL | PIN_HIGH);
+	if (err)
+		return err;
+
+	/*
+	 * And mark is as a globally pinned object to let the shrinker know
+	 * it cannot reclaim the object until we release it.
+	 */
+	vma->obj->pin_global++;
+
+	return 0;
+}
+
+static void __context_unpin(struct intel_context *ce)
+{
+	struct i915_vma *vma;
+
+	vma = ce->state;
+	if (!vma)
+		return;
+
+	vma->obj->pin_global--;
+	i915_vma_unpin(vma);
+}
+
+static void intel_ring_context_unpin(struct intel_context *ce)
+{
+	__context_unpin(ce);
+
+	i915_gem_context_put(ce->gem_context);
 }
 
 static struct i915_vma *
@@ -1311,13 +1334,9 @@ __ring_context_pin(struct intel_engine_cs *engine,
 		ce->state = vma;
 	}
 
-	if (ce->state) {
-		err = __context_pin(ce);
-		if (err)
-			goto err;
-
-		ce->state->obj->pin_global++;
-	}
+	err = __context_pin(ce);
+	if (err)
+		goto err;
 
 	i915_gem_context_get(ctx);