dma-buf: start caching of sg_table objects v2

To allow a smooth transition from pinning buffer objects to dynamic
invalidation we first start to cache the sg_table for an attachment.

v2: keep closer to the DRM implementation

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.kernel.org/patch/10943053/

include/linux/dma-buf.h

@@ -44,6 +44,15 @@ struct dma_buf_attachment;
  * @vunmap: [optional] unmaps a vmap from the buffer
  */
 struct dma_buf_ops {
+	/**
+	  * @cache_sgt_mapping:
+	  *
+	  * If true the framework will cache the first mapping made for each
+	  * attachment. This avoids creating mappings for attachments multiple
+	  * times.
+	  */
+	bool cache_sgt_mapping;
+
 	/**
 	 * @attach:
 	 *
@@ -323,6 +332,8 @@ struct dma_buf {
  * @dmabuf: buffer for this attachment.
  * @dev: device attached to the buffer.
  * @node: list of dma_buf_attachment.
+ * @sgt: cached mapping.
+ * @dir: direction of cached mapping.
  * @priv: exporter specific attachment data.
  *
  * This structure holds the attachment information between the dma_buf buffer
@@ -338,6 +349,8 @@ struct dma_buf_attachment {
 	struct dma_buf *dmabuf;
 	struct device *dev;
 	struct list_head node;
+	struct sg_table *sgt;
+	enum dma_data_direction dir;
 	void *priv;
 };