drm/ttm: add ttm_bo_init_reserved

This variant of ttm_bo_init returns the validated buffer object with
the reservation lock held when resv == NULL. This is convenient for
callers that want to use the BO immediately, e.g. for initializing its
contents.
Signed-off-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/ttm/ttm_bo.c

@@ -1093,18 +1093,18 @@ int ttm_bo_validate(struct ttm_buffer_object *bo,
 }
 EXPORT_SYMBOL(ttm_bo_validate);
 
-int ttm_bo_init(struct ttm_bo_device *bdev,
-		struct ttm_buffer_object *bo,
-		unsigned long size,
-		enum ttm_bo_type type,
-		struct ttm_placement *placement,
-		uint32_t page_alignment,
-		bool interruptible,
-		struct file *persistent_swap_storage,
-		size_t acc_size,
-		struct sg_table *sg,
-		struct reservation_object *resv,
-		void (*destroy) (struct ttm_buffer_object *))
+int ttm_bo_init_reserved(struct ttm_bo_device *bdev,
+			 struct ttm_buffer_object *bo,
+			 unsigned long size,
+			 enum ttm_bo_type type,
+			 struct ttm_placement *placement,
+			 uint32_t page_alignment,
+			 bool interruptible,
+			 struct file *persistent_swap_storage,
+			 size_t acc_size,
+			 struct sg_table *sg,
+			 struct reservation_object *resv,
+			 void (*destroy) (struct ttm_buffer_object *))
 {
 	int ret = 0;
 	unsigned long num_pages;
@@ -1188,10 +1188,10 @@ int ttm_bo_init(struct ttm_bo_device *bdev,
 	if (likely(!ret))
 		ret = ttm_bo_validate(bo, placement, interruptible, false);
 
-	if (!resv)
-		ttm_bo_unreserve(bo);
-
 	if (unlikely(ret)) {
+		if (!resv)
+			ttm_bo_unreserve(bo);
+
 		ttm_bo_unref(&bo);
 		return ret;
 	}
@@ -1204,6 +1204,35 @@ int ttm_bo_init(struct ttm_bo_device *bdev,
 
 	return ret;
 }
+EXPORT_SYMBOL(ttm_bo_init_reserved);
+
+int ttm_bo_init(struct ttm_bo_device *bdev,
+		struct ttm_buffer_object *bo,
+		unsigned long size,
+		enum ttm_bo_type type,
+		struct ttm_placement *placement,
+		uint32_t page_alignment,
+		bool interruptible,
+		struct file *persistent_swap_storage,
+		size_t acc_size,
+		struct sg_table *sg,
+		struct reservation_object *resv,
+		void (*destroy) (struct ttm_buffer_object *))
+{
+	int ret;
+
+	ret = ttm_bo_init_reserved(bdev, bo, size, type, placement,
+				   page_alignment, interruptible,
+				   persistent_swap_storage, acc_size,
+				   sg, resv, destroy);
+	if (ret)
+		return ret;
+
+	if (!resv)
+		ttm_bo_unreserve(bo);
+
+	return 0;
+}
 EXPORT_SYMBOL(ttm_bo_init);
 
 size_t ttm_bo_acc_size(struct ttm_bo_device *bdev,

include/drm/ttm/ttm_bo_api.h

@@ -439,6 +439,60 @@ size_t ttm_bo_dma_acc_size(struct ttm_bo_device *bdev,
 			   unsigned long bo_size,
 			   unsigned struct_size);
 
+/**
+ * ttm_bo_init_reserved
+ *
+ * @bdev: Pointer to a ttm_bo_device struct.
+ * @bo: Pointer to a ttm_buffer_object to be initialized.
+ * @size: Requested size of buffer object.
+ * @type: Requested type of buffer object.
+ * @flags: Initial placement flags.
+ * @page_alignment: Data alignment in pages.
+ * @interruptible: If needing to sleep to wait for GPU resources,
+ * sleep interruptible.
+ * @persistent_swap_storage: Usually the swap storage is deleted for buffers
+ * pinned in physical memory. If this behaviour is not desired, this member
+ * holds a pointer to a persistent shmem object. Typically, this would
+ * point to the shmem object backing a GEM object if TTM is used to back a
+ * GEM user interface.
+ * @acc_size: Accounted size for this object.
+ * @resv: Pointer to a reservation_object, or NULL to let ttm allocate one.
+ * @destroy: Destroy function. Use NULL for kfree().
+ *
+ * This function initializes a pre-allocated struct ttm_buffer_object.
+ * As this object may be part of a larger structure, this function,
+ * together with the @destroy function,
+ * enables driver-specific objects derived from a ttm_buffer_object.
+ *
+ * On successful return, the caller owns an object kref to @bo. The kref and
+ * list_kref are usually set to 1, but note that in some situations, other
+ * tasks may already be holding references to @bo as well.
+ * Furthermore, if resv == NULL, the buffer's reservation lock will be held,
+ * and it is the caller's responsibility to call ttm_bo_unreserve.
+ *
+ * If a failure occurs, the function will call the @destroy function, or
+ * kfree() if @destroy is NULL. Thus, after a failure, dereferencing @bo is
+ * illegal and will likely cause memory corruption.
+ *
+ * Returns
+ * -ENOMEM: Out of memory.
+ * -EINVAL: Invalid placement flags.
+ * -ERESTARTSYS: Interrupted by signal while sleeping waiting for resources.
+ */
+
+extern int ttm_bo_init_reserved(struct ttm_bo_device *bdev,
+				struct ttm_buffer_object *bo,
+				unsigned long size,
+				enum ttm_bo_type type,
+				struct ttm_placement *placement,
+				uint32_t page_alignment,
+				bool interrubtible,
+				struct file *persistent_swap_storage,
+				size_t acc_size,
+				struct sg_table *sg,
+				struct reservation_object *resv,
+				void (*destroy) (struct ttm_buffer_object *));
+
 /**
  * ttm_bo_init
  *