ttm: add prime sharing support to TTM (v2)

This adds the ability for ttm common code to take an SG table
and use it as the backing for a slave TTM object.

The drivers can then populate their GTT tables using the SG object.

v2: make sure to setup VM for sg bos as well.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

include/drm/ttm/ttm_bo_api.h

@@ -124,11 +124,15 @@ struct ttm_mem_reg {
  *
  * @ttm_bo_type_kernel: These buffers are like ttm_bo_type_device buffers,
  * but they cannot be accessed from user-space. For kernel-only use.
+ *
+ * @ttm_bo_type_sg: Buffer made from dmabuf sg table shared with another
+ * driver.
  */
 
 enum ttm_bo_type {
 	ttm_bo_type_device,
-	ttm_bo_type_kernel
+	ttm_bo_type_kernel,
+	ttm_bo_type_sg
 };
 
 struct ttm_tt;
@@ -271,6 +275,8 @@ struct ttm_buffer_object {
 
 	unsigned long offset;
 	uint32_t cur_placement;
+
+	struct sg_table *sg;
 };
 
 /**
@@ -503,6 +509,7 @@ extern int ttm_bo_init(struct ttm_bo_device *bdev,
 			bool interrubtible,
 			struct file *persistent_swap_storage,
 			size_t acc_size,
+			struct sg_table *sg,
 			void (*destroy) (struct ttm_buffer_object *));
 
 /**