[PATCH] drm: Replace kref with a simple atomic reference count

[Chris Wilson]

For a deferred-free cache of unreferenced bound objects, a simple
reference count is required without the baggage of kref.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/drm_gem.c  |   12 +++---------
 drivers/gpu/drm/drm_info.c |    2 +-
 include/drm/drmP.h         |   16 +++++++++-------
 3 files changed, 13 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index ea1c4b0..874e776 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -141,7 +141,7 @@ int drm_gem_object_init(struct drm_device *dev,
 	if (IS_ERR(obj->filp))
 		return -ENOMEM;
 
-	kref_init(&obj->refcount);
+	atomic_set(&obj->refcount, 1);
 	atomic_set(&obj->handle_count, 0);
 	obj->size = size;
 
@@ -436,9 +436,8 @@ EXPORT_SYMBOL(drm_gem_object_release);
  * Frees the object
  */
 void
-drm_gem_object_free(struct kref *kref)
+drm_gem_object_free(struct drm_gem_object *obj)
 {
-	struct drm_gem_object *obj = (struct drm_gem_object *) kref;
 	struct drm_device *dev = obj->dev;
 
 	BUG_ON(!mutex_is_locked(&dev->struct_mutex));
@@ -448,11 +447,6 @@ drm_gem_object_free(struct kref *kref)
 }
 EXPORT_SYMBOL(drm_gem_object_free);
 
-static void drm_gem_object_ref_bug(struct kref *list_kref)
-{
-	BUG();
-}
-
 /**
  * Called after the last handle to the object has been closed
  *
@@ -476,7 +470,7 @@ void drm_gem_object_handle_free(struct drm_gem_object *obj)
 		*
 		* This cannot be the last reference, since the handle holds one too.
 		 */
-		kref_put(&obj->refcount, drm_gem_object_ref_bug);
+		atomic_dec(&obj->refcount);
 	} else
 		spin_unlock(&dev->object_name_lock);
 
diff --git a/drivers/gpu/drm/drm_info.c b/drivers/gpu/drm/drm_info.c
index 3cdbaf3..4a80bd8 100644
--- a/drivers/gpu/drm/drm_info.c
+++ b/drivers/gpu/drm/drm_info.c
@@ -256,7 +256,7 @@ int drm_gem_one_name_info(int id, void *ptr, void *data)
 	seq_printf(m, "%6d %8zd %7d %8d\n",
 		   obj->name, obj->size,
 		   atomic_read(&obj->handle_count),
-		   atomic_read(&obj->refcount.refcount));
+		   atomic_read(&obj->refcount));
 	return 0;
 }
 
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index 2b33980..f332c56 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -609,7 +609,7 @@ struct drm_gem_mm {
  */
 struct drm_gem_object {
 	/** Reference count of this object */
-	struct kref refcount;
+	atomic_t refcount;
 
 	/** Handle count of this object. Each handle also holds a reference */
 	atomic_t handle_count; /* number of handles on this object */
@@ -1504,7 +1504,7 @@ extern void drm_sysfs_connector_remove(struct drm_connector *connector);
 int drm_gem_init(struct drm_device *dev);
 void drm_gem_destroy(struct drm_device *dev);
 void drm_gem_object_release(struct drm_gem_object *obj);
-void drm_gem_object_free(struct kref *kref);
+void drm_gem_object_free(struct drm_gem_object *obj);
 struct drm_gem_object *drm_gem_object_alloc(struct drm_device *dev,
 					    size_t size);
 int drm_gem_object_init(struct drm_device *dev,
@@ -1519,23 +1519,25 @@ int drm_gem_mmap(struct file *filp, struct vm_area_struct *vma);
 static inline void
 drm_gem_object_reference(struct drm_gem_object *obj)
 {
-	kref_get(&obj->refcount);
+	atomic_inc(&obj->refcount);
+	smp_mb__after_atomic_inc();
 }
 
 static inline void
 drm_gem_object_unreference(struct drm_gem_object *obj)
 {
-	if (obj != NULL)
-		kref_put(&obj->refcount, drm_gem_object_free);
+	if (obj != NULL && atomic_dec_and_test(&obj->refcount))
+		drm_gem_object_free(obj);
 }
 
 static inline void
 drm_gem_object_unreference_unlocked(struct drm_gem_object *obj)
 {
-	if (obj != NULL) {
+	if (obj != NULL && atomic_dec_and_test(&obj->refcount)) {
 		struct drm_device *dev = obj->dev;
 		mutex_lock(&dev->struct_mutex);
-		kref_put(&obj->refcount, drm_gem_object_free);
+		if (atomic_read(&obj->refcount) == 0)
+			drm_gem_object_free(obj);
 		mutex_unlock(&dev->struct_mutex);
 	}
 }
-- 
1.7.2.3