drm/i915: Add getter/setter for i915_gem_object->frontbuffer

Add getter/setter for i915_gem_object->frontbuffer and use it instead of
directly touching i915_gem_object->frontbuffer frontbuffer pointer.

v3:
 - Fix intel_frontbuffer_get return value
 - s/front_ret/cur/
v2: Move getter/setter into i915_gem_object.h
Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230727064142.751976-3-jouni.hogander@intel.com

drivers/gpu/drm/i915/display/intel_frontbuffer.c

@@ -237,7 +237,7 @@ static void frontbuffer_release(struct kref *ref)
 	}
 	spin_unlock(&obj->vma.lock);
 
-	RCU_INIT_POINTER(obj->frontbuffer, NULL);
+	i915_gem_object_set_frontbuffer(obj, NULL);
 	spin_unlock(&intel_bo_to_i915(obj)->display.fb_tracking.lock);
 
 	i915_active_fini(&front->write);
@@ -250,9 +250,9 @@ struct intel_frontbuffer *
 intel_frontbuffer_get(struct drm_i915_gem_object *obj)
 {
 	struct drm_i915_private *i915 = intel_bo_to_i915(obj);
-	struct intel_frontbuffer *front;
+	struct intel_frontbuffer *front, *cur;
 
-	front = __intel_frontbuffer_get(obj);
+	front = i915_gem_object_get_frontbuffer(obj);
 	if (front)
 		return front;
 
@@ -269,17 +269,11 @@ intel_frontbuffer_get(struct drm_i915_gem_object *obj)
 			 I915_ACTIVE_RETIRE_SLEEPS);
 
 	spin_lock(&i915->display.fb_tracking.lock);
-	if (rcu_access_pointer(obj->frontbuffer)) {
-		kfree(front);
-		front = rcu_dereference_protected(obj->frontbuffer, true);
-		kref_get(&front->ref);
-	} else {
-		i915_gem_object_get(obj);
-		rcu_assign_pointer(obj->frontbuffer, front);
-	}
+	cur = i915_gem_object_set_frontbuffer(obj, front);
 	spin_unlock(&i915->display.fb_tracking.lock);
-
-	return front;
+	if (cur != front)
+		kfree(front);
+	return cur;
 }
 
 void intel_frontbuffer_put(struct intel_frontbuffer *front)

drivers/gpu/drm/i915/display/intel_frontbuffer.h

@@ -75,33 +75,6 @@ void intel_frontbuffer_flip(struct drm_i915_private *i915,
 
 void intel_frontbuffer_put(struct intel_frontbuffer *front);
 
-static inline struct intel_frontbuffer *
-__intel_frontbuffer_get(const struct drm_i915_gem_object *obj)
-{
-	struct intel_frontbuffer *front;
-
-	if (likely(!rcu_access_pointer(obj->frontbuffer)))
-		return NULL;
-
-	rcu_read_lock();
-	do {
-		front = rcu_dereference(obj->frontbuffer);
-		if (!front)
-			break;
-
-		if (unlikely(!kref_get_unless_zero(&front->ref)))
-			continue;
-
-		if (likely(front == rcu_access_pointer(obj->frontbuffer)))
-			break;
-
-		intel_frontbuffer_put(front);
-	} while (1);
-	rcu_read_unlock();
-
-	return front;
-}
-
 struct intel_frontbuffer *
 intel_frontbuffer_get(struct drm_i915_gem_object *obj);
 

drivers/gpu/drm/i915/gem/i915_gem_object.c

@@ -469,7 +469,7 @@ void __i915_gem_object_flush_frontbuffer(struct drm_i915_gem_object *obj,
 {
 	struct intel_frontbuffer *front;
 
-	front = __intel_frontbuffer_get(obj);
+	front = i915_gem_object_get_frontbuffer(obj);
 	if (front) {
 		intel_frontbuffer_flush(front, origin);
 		intel_frontbuffer_put(front);
@@ -481,7 +481,7 @@ void __i915_gem_object_invalidate_frontbuffer(struct drm_i915_gem_object *obj,
 {
 	struct intel_frontbuffer *front;
 
-	front = __intel_frontbuffer_get(obj);
+	front = i915_gem_object_get_frontbuffer(obj);
 	if (front) {
 		intel_frontbuffer_invalidate(front, origin);
 		intel_frontbuffer_put(front);

drivers/gpu/drm/i915/gem/i915_gem_object.h

@@ -891,4 +891,71 @@ static inline int i915_gem_object_userptr_validate(struct drm_i915_gem_object *o
 
 #endif
 
+/**
+ * i915_gem_object_get_frontbuffer - Get the object's frontbuffer
+ * @obj: The object whose frontbuffer to get.
+ *
+ * Get pointer to object's frontbuffer if such exists. Please note that RCU
+ * mechanism is used to handle e.g. ongoing removal of frontbuffer pointer.
+ *
+ * Return: pointer to object's frontbuffer is such exists or NULL
+ */
+static inline struct intel_frontbuffer *
+i915_gem_object_get_frontbuffer(const struct drm_i915_gem_object *obj)
+{
+	struct intel_frontbuffer *front;
+
+	if (likely(!rcu_access_pointer(obj->frontbuffer)))
+		return NULL;
+
+	rcu_read_lock();
+	do {
+		front = rcu_dereference(obj->frontbuffer);
+		if (!front)
+			break;
+
+		if (unlikely(!kref_get_unless_zero(&front->ref)))
+			continue;
+
+		if (likely(front == rcu_access_pointer(obj->frontbuffer)))
+			break;
+
+		intel_frontbuffer_put(front);
+	} while (1);
+	rcu_read_unlock();
+
+	return front;
+}
+
+/**
+ * i915_gem_object_set_frontbuffer - Set the object's frontbuffer
+ * @obj: The object whose frontbuffer to set.
+ * @front: The frontbuffer to set
+ *
+ * Set object's frontbuffer pointer. If frontbuffer is already set for the
+ * object keep it and return it's pointer to the caller. Please note that RCU
+ * mechanism is used to handle e.g. ongoing removal of frontbuffer pointer. This
+ * function is protected by i915->display.fb_tracking.lock
+ *
+ * Return: pointer to frontbuffer which was set.
+ */
+static inline struct intel_frontbuffer *
+i915_gem_object_set_frontbuffer(struct drm_i915_gem_object *obj,
+				struct intel_frontbuffer *front)
+{
+	struct intel_frontbuffer *cur = front;
+
+	if (!front) {
+		RCU_INIT_POINTER(obj->frontbuffer, NULL);
+	} else if (rcu_access_pointer(obj->frontbuffer)) {
+		cur = rcu_dereference_protected(obj->frontbuffer, true);
+		kref_get(&cur->ref);
+	} else {
+		drm_gem_object_get(intel_bo_to_drm_bo(obj));
+		rcu_assign_pointer(obj->frontbuffer, front);
+	}
+
+	return cur;
+}
+
 #endif

drivers/gpu/drm/i915/i915_vma.c

@@ -1908,7 +1908,7 @@ int _i915_vma_move_to_active(struct i915_vma *vma,
 	if (flags & EXEC_OBJECT_WRITE) {
 		struct intel_frontbuffer *front;
 
-		front = __intel_frontbuffer_get(obj);
+		front = i915_gem_object_get_frontbuffer(obj);
 		if (unlikely(front)) {
 			if (intel_frontbuffer_invalidate(front, ORIGIN_CS))
 				i915_active_add_request(&front->write, rq);