[PATCH v4 4/4] 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 dbuf_duplicated boolean 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>
---
v4
- Only set dbuf_duplicated when alloc_devs are equal.

v3
- Adjust the patch according to the previous patches to resolve conflicts.
- Add comment to explain the purpose of the change.

v2
- Separate out the refactor changes out to previous patches.
- Fix mem_priv check.
---
 .../media/common/videobuf2/videobuf2-core.c   | 30 ++++++++++++++++---
 include/media/videobuf2-core.h                |  3 ++
 2 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
index cbc8928f0418..c19f1df3a4d2 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->dbuf_duplicated) {
+		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;
@@ -316,6 +319,7 @@ static void __vb2_plane_dmabuf_put(struct vb2_buffer *vb, struct vb2_plane *p)
 	p->length = 0;
 	p->m.fd = 0;
 	p->data_offset = 0;
+	p->dbuf_duplicated = false;
 }
 
 /*
@@ -1374,7 +1378,7 @@ 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;
 
@@ -1427,6 +1431,24 @@ static int __prepare_dmabuf(struct vb2_buffer *vb)
 		}
 
 		for (plane = 0; plane < vb->num_planes; ++plane) {
+			/*
+			 * This is an optimization to reduce dma_buf attachment/mapping.
+			 * When the same dma_buf is used for multiple planes, there is no need
+			 * to create duplicated attachments.
+			 */
+			for (i = 0; i < plane; ++i) {
+				if (planes[plane].dbuf == vb->planes[i].dbuf &&
+				    q->alloc_devs[plane] == q->alloc_devs[i]) {
+					vb->planes[plane].dbuf_duplicated = true;
+					vb->planes[plane].dbuf = vb->planes[i].dbuf;
+					vb->planes[plane].mem_priv = vb->planes[i].mem_priv;
+					break;
+				}
+			}
+
+			if (vb->planes[plane].dbuf_duplicated)
+				continue;
+
 			/* Acquire each plane's memory */
 			mem_priv = call_ptr_memop(attach_dmabuf,
 						  vb,
diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index 955237ac503d..053ced60595f 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			dbuf_duplicated;
 	unsigned int		bytesused;
 	unsigned int		length;
 	unsigned int		min_length;
-- 
2.45.2.627.g7a2c4fd464-goog