[RFC PATCH] media: videobuf2-core: attach once if multiple planes share the same dbuf

[Yunke Cao <yunkec@xxxxxxxxxxxx>]

When multiple planes use the same dma buf, each plane will have its own dma
buf attachment and mapping. It is a waste of IOVA space.

This patch adds a duplicated_dbuf flag in vb2_plane. If a plane's dbuf
is the same as an existing plane, do not create another attachment and
mapping.

Signed-off-by: Yunke Cao <yunkec@xxxxxxxxxxxx>
---
 .../media/common/videobuf2/videobuf2-core.c   | 30 +++++++++++++++----
 include/media/videobuf2-core.h                |  3 ++
 2 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
index b6bf8f232f48..b03e058ef2b1 100644
--- a/drivers/media/common/videobuf2/videobuf2-core.c
+++ b/drivers/media/common/videobuf2/videobuf2-core.c
@@ -304,10 +304,13 @@ static void __vb2_plane_dmabuf_put(struct vb2_buffer *vb, struct vb2_plane *p)
 	if (!p->mem_priv)
 		return;
 
-	if (p->dbuf_mapped)
-		call_void_memop(vb, unmap_dmabuf, p->mem_priv);
+	if (!p->duplicated_dbuf) {
+		if (p->dbuf_mapped)
+			call_void_memop(vb, unmap_dmabuf, p->mem_priv);
+
+		call_void_memop(vb, detach_dmabuf, p->mem_priv);
+	}
 
-	call_void_memop(vb, detach_dmabuf, p->mem_priv);
 	dma_buf_put(p->dbuf);
 	p->mem_priv = NULL;
 	p->dbuf = NULL;
@@ -1327,7 +1330,7 @@ static int __prepare_dmabuf(struct vb2_buffer *vb)
 	struct vb2_plane planes[VB2_MAX_PLANES];
 	struct vb2_queue *q = vb->vb2_queue;
 	void *mem_priv;
-	unsigned int plane;
+	unsigned int plane, i;
 	int ret = 0;
 	bool reacquired = vb->planes[0].mem_priv == NULL;
 
@@ -1383,6 +1386,22 @@ static int __prepare_dmabuf(struct vb2_buffer *vb)
 		vb->planes[plane].m.fd = 0;
 		vb->planes[plane].data_offset = 0;
 
+		if (mem_priv && plane > 0) {
+			for (i = 0; i < plane; ++i) {
+				if (dbuf == vb->planes[i].dbuf) {
+					vb->planes[plane].duplicated_dbuf = true;
+					break;
+				}
+			}
+		}
+
+		/* There's no need to attach a duplicated dbuf. */
+		if (vb->planes[plane].duplicated_dbuf) {
+			vb->planes[plane].dbuf = dbuf;
+			vb->planes[plane].mem_priv = mem_priv;
+			continue;
+		}
+
 		/* Acquire each plane's memory */
 		mem_priv = call_ptr_memop(attach_dmabuf,
 					  vb,
@@ -1396,6 +1415,7 @@ static int __prepare_dmabuf(struct vb2_buffer *vb)
 			goto err;
 		}
 
+		vb->planes[plane].duplicated_dbuf = false;
 		vb->planes[plane].dbuf = dbuf;
 		vb->planes[plane].mem_priv = mem_priv;
 	}
@@ -1406,7 +1426,7 @@ static int __prepare_dmabuf(struct vb2_buffer *vb)
 	 * userspace knows sooner rather than later if the dma-buf map fails.
 	 */
 	for (plane = 0; plane < vb->num_planes; ++plane) {
-		if (vb->planes[plane].dbuf_mapped)
+		if (vb->planes[plane].dbuf_mapped || vb->planes[plane].duplicated_dbuf)
 			continue;
 
 		ret = call_memop(vb, map_dmabuf, vb->planes[plane].mem_priv);
diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index 8b86996b2719..5db781da2ebc 100644
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -154,6 +154,8 @@ struct vb2_mem_ops {
  * @mem_priv:	private data with this plane.
  * @dbuf:	dma_buf - shared buffer object.
  * @dbuf_mapped:	flag to show whether dbuf is mapped or not
+ * @duplicated_dbuf:	boolean to show whether dbuf is duplicated with a
+ *		previous plane of the buffer.
  * @bytesused:	number of bytes occupied by data in the plane (payload).
  * @length:	size of this plane (NOT the payload) in bytes. The maximum
  *		valid size is MAX_UINT - PAGE_SIZE.
@@ -179,6 +181,7 @@ struct vb2_plane {
 	void			*mem_priv;
 	struct dma_buf		*dbuf;
 	unsigned int		dbuf_mapped;
+	bool			duplicated_dbuf;
 	unsigned int		bytesused;
 	unsigned int		length;
 	unsigned int		min_length;
-- 
2.44.0.478.gd926399ef9-goog