allow buffers allocation with DMABUF memory type

Message ID 1429780973-22006-1-git-send-email-benjamin.gaignard@linaro.org
State New
Headers show

Commit Message

Benjamin Gaignard April 23, 2015, 9:22 a.m.
Until now the only way to make the driver allocate buffers and
share them using dma_buf was to use V4L2_MEMORY_MMAP memory type.
Use of MMAP memory type is a problem because vb2 never call
dma_buf_map_attachment() to attach itself while queuing the buffer
so dma_buf importer will not know that another device use this buffer.

This patch allow to allocate buffer even for DMABUF memory type
and correctly manage dma_buf buffer attachment.

vb2_mem_ops attach_dmabuf() prototype has been changed to be able
to distinguish if the attachment is done on a already existing
buffer or on imported one.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
---
 drivers/media/v4l2-core/videobuf2-core.c       | 76 ++++++++++++++++++++++++--
 drivers/media/v4l2-core/videobuf2-dma-contig.c | 10 ++--
 drivers/media/v4l2-core/videobuf2-dma-sg.c     |  8 ++-
 drivers/media/v4l2-core/videobuf2-vmalloc.c    |  8 ++-
 include/media/videobuf2-core.h                 |  5 +-
 5 files changed, 91 insertions(+), 16 deletions(-)

Comments

Hans Verkuil Feb. 13, 2017, 12:18 p.m. | #1
Hi Benjamin,

This is a blast from the past since this patch is almost two years old and it
has been languishing in my TODO list for ages. Sorry about that.

Obviously this patch no longer applies, but I was also wondering what exactly
will go wrong if we don't attach to the dma buf.

If something would go wrong, then I would expect to see the attach happen when
the MMAP buffer is exported as a dmabuf fd. Until it is turned into a dmabuf there
is no need to attach at all.

It all looks very weird to me, but that might be the reason why you never pursued
this patch in the first place.

Regards,

	Hans

On 04/23/2015 11:22 AM, Benjamin Gaignard wrote:
> Until now the only way to make the driver allocate buffers and

> share them using dma_buf was to use V4L2_MEMORY_MMAP memory type.

> Use of MMAP memory type is a problem because vb2 never call

> dma_buf_map_attachment() to attach itself while queuing the buffer

> so dma_buf importer will not know that another device use this buffer.

> 

> This patch allow to allocate buffer even for DMABUF memory type

> and correctly manage dma_buf buffer attachment.

> 

> vb2_mem_ops attach_dmabuf() prototype has been changed to be able

> to distinguish if the attachment is done on a already existing

> buffer or on imported one.

> 

> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>

> ---

>  drivers/media/v4l2-core/videobuf2-core.c       | 76 ++++++++++++++++++++++++--

>  drivers/media/v4l2-core/videobuf2-dma-contig.c | 10 ++--

>  drivers/media/v4l2-core/videobuf2-dma-sg.c     |  8 ++-

>  drivers/media/v4l2-core/videobuf2-vmalloc.c    |  8 ++-

>  include/media/videobuf2-core.h                 |  5 +-

>  5 files changed, 91 insertions(+), 16 deletions(-)

> 

> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c

> index 1329dcc..c5968aa 100644

> --- a/drivers/media/v4l2-core/videobuf2-core.c

> +++ b/drivers/media/v4l2-core/videobuf2-core.c

> @@ -337,6 +337,67 @@ static void __setup_offsets(struct vb2_queue *q, unsigned int n)

>  }

>  

>  /**

> + * __setup_dmabufs() - setup dmabuf fd for every plane in

> + * every buffer on the queue

> + */

> +static void __setup_dmabufs(struct vb2_queue *q, unsigned int n)

> +{

> +	unsigned int buffer, plane;

> +	struct vb2_buffer *vb;

> +	struct vb2_plane *vb_plane;

> +	struct dma_buf *dbuf;

> +	void *mem_priv;

> +	int fd;

> +	int write = !V4L2_TYPE_IS_OUTPUT(q->type);

> +	int flags = write ? O_WRONLY : O_RDONLY;

> +

> +	for (buffer = q->num_buffers; buffer < q->num_buffers + n; ++buffer) {

> +		vb = q->bufs[buffer];

> +		if (!vb)

> +			continue;

> +

> +		for (plane = 0; plane < vb->num_planes; ++plane) {

> +			vb_plane = &vb->planes[plane];

> +

> +			dbuf = call_ptr_memop(vb, get_dmabuf,

> +					      vb_plane->mem_priv,

> +					      flags & O_ACCMODE);

> +			if (IS_ERR_OR_NULL(dbuf)) {

> +				dprintk(1, "Failed to export buffer %d, " \

> +					"plane %d\n", buffer, plane);

> +				continue;

> +			}

> +

> +			fd = dma_buf_fd(dbuf, flags & ~O_ACCMODE);

> +			if (fd < 0) {

> +				dprintk(3, "buffer %d, plane %d failed " \

> +					"to export (%d)\n", buffer, plane, fd);

> +				dma_buf_put(dbuf);

> +				continue;

> +			}

> +

> +			/* Acquire each plane's memory */

> +			mem_priv = call_ptr_memop(vb, attach_dmabuf,

> +						  q->alloc_ctx[plane], dbuf,

> +						  vb->v4l2_planes[plane].length,

> +						  write, vb_plane->mem_priv);

> +			if (IS_ERR(mem_priv)) {

> +				dprintk(1, "Buffer %d plane %d failed "\

> +					"to attach dmabuf\n", buffer, plane);

> +				dma_buf_put(dbuf);

> +				continue;

> +			}

> +

> +			vb_plane->dbuf = dbuf;

> +			vb->v4l2_planes[plane].m.fd = fd;

> +

> +			dprintk(3, "Buffer %d, plane %d fd %x\n",

> +				buffer, plane, fd);

> +		}

> +	}

> +}

> +

> +/**

>   * __vb2_queue_alloc() - allocate videobuf buffer structures and (for MMAP type)

>   * video buffer memory for all buffers/planes on the queue and initializes the

>   * queue

> @@ -369,8 +430,9 @@ static int __vb2_queue_alloc(struct vb2_queue *q, enum v4l2_memory memory,

>  		vb->v4l2_buf.type = q->type;

>  		vb->v4l2_buf.memory = memory;

>  

> -		/* Allocate video buffer memory for the MMAP type */

> -		if (memory == V4L2_MEMORY_MMAP) {

> +		/* Allocate video buffer memory for the MMAP and DMABUF types */

> +		if (memory == V4L2_MEMORY_MMAP ||

> +		    memory == V4L2_MEMORY_DMABUF) {

>  			ret = __vb2_buf_mem_alloc(vb);

>  			if (ret) {

>  				dprintk(1, "failed allocating memory for "

> @@ -400,6 +462,9 @@ static int __vb2_queue_alloc(struct vb2_queue *q, enum v4l2_memory memory,

>  	if (memory == V4L2_MEMORY_MMAP)

>  		__setup_offsets(q, buffer);

>  

> +	if (memory == V4L2_MEMORY_DMABUF)

> +		__setup_dmabufs(q, buffer);

> +

>  	dprintk(1, "allocated %d buffers, %d plane(s) each\n",

>  			buffer, num_planes);

>  

> @@ -859,7 +924,7 @@ static int __verify_memory_type(struct vb2_queue *q,

>   *    to be used during streaming,

>   * 4) allocates internal buffer structures (struct vb2_buffer), according to

>   *    the agreed parameters,

> - * 5) for MMAP memory type, allocates actual video memory, using the

> + * 5) for MMAP and DMABUF memory types, allocates actual video memory, using the

>   *    memory handling/allocation routines provided during queue initialization

>   *

>   * If req->count is 0, all the memory will be freed instead.

> @@ -885,7 +950,8 @@ static int __reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req)

>  		 * are not in use and can be freed.

>  		 */

>  		mutex_lock(&q->mmap_lock);

> -		if (q->memory == V4L2_MEMORY_MMAP && __buffers_in_use(q)) {

> +		if ((q->memory == V4L2_MEMORY_MMAP ||

> +		     q->memory == V4L2_MEMORY_DMABUF) && __buffers_in_use(q)) {

>  			mutex_unlock(&q->mmap_lock);

>  			dprintk(1, "memory in use, cannot free\n");

>  			return -EBUSY;

> @@ -1540,7 +1606,7 @@ static int __qbuf_dmabuf(struct vb2_buffer *vb, const struct v4l2_buffer *b)

>  

>  		/* Acquire each plane's memory */

>  		mem_priv = call_ptr_memop(vb, attach_dmabuf, q->alloc_ctx[plane],

> -			dbuf, planes[plane].length, dma_dir);

> +			dbuf, planes[plane].length, dma_dir, NULL);

>  		if (IS_ERR(mem_priv)) {

>  			dprintk(1, "failed to attach dmabuf\n");

>  			ret = PTR_ERR(mem_priv);

> diff --git a/drivers/media/v4l2-core/videobuf2-dma-contig.c b/drivers/media/v4l2-core/videobuf2-dma-contig.c

> index b481d20..8dc945e 100644

> --- a/drivers/media/v4l2-core/videobuf2-dma-contig.c

> +++ b/drivers/media/v4l2-core/videobuf2-dma-contig.c

> @@ -793,7 +793,7 @@ static void vb2_dc_detach_dmabuf(void *mem_priv)

>  	struct vb2_dc_buf *buf = mem_priv;

>  

>  	/* if vb2 works correctly you should never detach mapped buffer */

> -	if (WARN_ON(buf->dma_addr))

> +	if (WARN_ON(buf->dma_sgt))

>  		vb2_dc_unmap_dmabuf(buf);

>  

>  	/* detach this attachment */

> @@ -802,16 +802,18 @@ static void vb2_dc_detach_dmabuf(void *mem_priv)

>  }

>  

>  static void *vb2_dc_attach_dmabuf(void *alloc_ctx, struct dma_buf *dbuf,

> -	unsigned long size, enum dma_data_direction dma_dir)

> +	unsigned long size, enum dma_data_direction dma_dir, void *buf_priv)

>  {

>  	struct vb2_dc_conf *conf = alloc_ctx;

> -	struct vb2_dc_buf *buf;

> +	struct vb2_dc_buf *buf = buf_priv;

>  	struct dma_buf_attachment *dba;

>  

>  	if (dbuf->size < size)

>  		return ERR_PTR(-EFAULT);

>  

> -	buf = kzalloc(sizeof(*buf), GFP_KERNEL);

> +	if (!buf)

> +		buf = kzalloc(sizeof(*buf), GFP_KERNEL);

> +

>  	if (!buf)

>  		return ERR_PTR(-ENOMEM);

>  

> diff --git a/drivers/media/v4l2-core/videobuf2-dma-sg.c b/drivers/media/v4l2-core/videobuf2-dma-sg.c

> index b1838ab..b9855fd 100644

> --- a/drivers/media/v4l2-core/videobuf2-dma-sg.c

> +++ b/drivers/media/v4l2-core/videobuf2-dma-sg.c

> @@ -667,16 +667,18 @@ static void vb2_dma_sg_detach_dmabuf(void *mem_priv)

>  }

>  

>  static void *vb2_dma_sg_attach_dmabuf(void *alloc_ctx, struct dma_buf *dbuf,

> -	unsigned long size, enum dma_data_direction dma_dir)

> +	unsigned long size, enum dma_data_direction dma_dir, void *buf_priv)

>  {

>  	struct vb2_dma_sg_conf *conf = alloc_ctx;

> -	struct vb2_dma_sg_buf *buf;

> +	struct vb2_dma_sg_buf *buf = buf_priv;

>  	struct dma_buf_attachment *dba;

>  

>  	if (dbuf->size < size)

>  		return ERR_PTR(-EFAULT);

>  

> -	buf = kzalloc(sizeof(*buf), GFP_KERNEL);

> +	if (!buf)

> +		buf = kzalloc(sizeof(*buf), GFP_KERNEL);

> +

>  	if (!buf)

>  		return ERR_PTR(-ENOMEM);

>  

> diff --git a/drivers/media/v4l2-core/videobuf2-vmalloc.c b/drivers/media/v4l2-core/videobuf2-vmalloc.c

> index bcde885..373294c 100644

> --- a/drivers/media/v4l2-core/videobuf2-vmalloc.c

> +++ b/drivers/media/v4l2-core/videobuf2-vmalloc.c

> @@ -416,14 +416,16 @@ static void vb2_vmalloc_detach_dmabuf(void *mem_priv)

>  }

>  

>  static void *vb2_vmalloc_attach_dmabuf(void *alloc_ctx, struct dma_buf *dbuf,

> -	unsigned long size, enum dma_data_direction dma_dir)

> +	unsigned long size, enum dma_data_direction dma_dir, void *buf_priv)

>  {

> -	struct vb2_vmalloc_buf *buf;

> +	struct vb2_vmalloc_buf *buf = buf_priv;

>  

>  	if (dbuf->size < size)

>  		return ERR_PTR(-EFAULT);

>  

> -	buf = kzalloc(sizeof(*buf), GFP_KERNEL);

> +	if (!buf)

> +		buf = kzalloc(sizeof(*buf), GFP_KERNEL);

> +

>  	if (!buf)

>  		return ERR_PTR(-ENOMEM);

>  

> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h

> index a5790fd..374b26b 100644

> --- a/include/media/videobuf2-core.h

> +++ b/include/media/videobuf2-core.h

> @@ -49,6 +49,8 @@ struct vb2_threadio_data;

>   *		   used for DMABUF memory types; alloc_ctx is the alloc context

>   *		   dbuf is the shared dma_buf; returns NULL on failure;

>   *		   allocator private per-buffer structure on success;

> + *		   if private per-buffer structure is provided reuse it

> + *		   instead of allocating a new one.

>   *		   this needs to be used for further accesses to the buffer.

>   * @detach_dmabuf: inform the exporter of the buffer that the current DMABUF

>   *		   buffer is no longer used; the buf_priv argument is the

> @@ -98,7 +100,8 @@ struct vb2_mem_ops {

>  

>  	void		*(*attach_dmabuf)(void *alloc_ctx, struct dma_buf *dbuf,

>  					  unsigned long size,

> -					  enum dma_data_direction dma_dir);

> +					  enum dma_data_direction dma_dir,

> +					  void *buf_priv);

>  	void		(*detach_dmabuf)(void *buf_priv);

>  	int		(*map_dmabuf)(void *buf_priv);

>  	void		(*unmap_dmabuf)(void *buf_priv);

>

Patch hide | download patch | download mbox

diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
index 1329dcc..c5968aa 100644
--- a/drivers/media/v4l2-core/videobuf2-core.c
+++ b/drivers/media/v4l2-core/videobuf2-core.c
@@ -337,6 +337,67 @@  static void __setup_offsets(struct vb2_queue *q, unsigned int n)
 }
 
 /**
+ * __setup_dmabufs() - setup dmabuf fd for every plane in
+ * every buffer on the queue
+ */
+static void __setup_dmabufs(struct vb2_queue *q, unsigned int n)
+{
+	unsigned int buffer, plane;
+	struct vb2_buffer *vb;
+	struct vb2_plane *vb_plane;
+	struct dma_buf *dbuf;
+	void *mem_priv;
+	int fd;
+	int write = !V4L2_TYPE_IS_OUTPUT(q->type);
+	int flags = write ? O_WRONLY : O_RDONLY;
+
+	for (buffer = q->num_buffers; buffer < q->num_buffers + n; ++buffer) {
+		vb = q->bufs[buffer];
+		if (!vb)
+			continue;
+
+		for (plane = 0; plane < vb->num_planes; ++plane) {
+			vb_plane = &vb->planes[plane];
+
+			dbuf = call_ptr_memop(vb, get_dmabuf,
+					      vb_plane->mem_priv,
+					      flags & O_ACCMODE);
+			if (IS_ERR_OR_NULL(dbuf)) {
+				dprintk(1, "Failed to export buffer %d, " \
+					"plane %d\n", buffer, plane);
+				continue;
+			}
+
+			fd = dma_buf_fd(dbuf, flags & ~O_ACCMODE);
+			if (fd < 0) {
+				dprintk(3, "buffer %d, plane %d failed " \
+					"to export (%d)\n", buffer, plane, fd);
+				dma_buf_put(dbuf);
+				continue;
+			}
+
+			/* Acquire each plane's memory */
+			mem_priv = call_ptr_memop(vb, attach_dmabuf,
+						  q->alloc_ctx[plane], dbuf,
+						  vb->v4l2_planes[plane].length,
+						  write, vb_plane->mem_priv);
+			if (IS_ERR(mem_priv)) {
+				dprintk(1, "Buffer %d plane %d failed "\
+					"to attach dmabuf\n", buffer, plane);
+				dma_buf_put(dbuf);
+				continue;
+			}
+
+			vb_plane->dbuf = dbuf;
+			vb->v4l2_planes[plane].m.fd = fd;
+
+			dprintk(3, "Buffer %d, plane %d fd %x\n",
+				buffer, plane, fd);
+		}
+	}
+}
+
+/**
  * __vb2_queue_alloc() - allocate videobuf buffer structures and (for MMAP type)
  * video buffer memory for all buffers/planes on the queue and initializes the
  * queue
@@ -369,8 +430,9 @@  static int __vb2_queue_alloc(struct vb2_queue *q, enum v4l2_memory memory,
 		vb->v4l2_buf.type = q->type;
 		vb->v4l2_buf.memory = memory;
 
-		/* Allocate video buffer memory for the MMAP type */
-		if (memory == V4L2_MEMORY_MMAP) {
+		/* Allocate video buffer memory for the MMAP and DMABUF types */
+		if (memory == V4L2_MEMORY_MMAP ||
+		    memory == V4L2_MEMORY_DMABUF) {
 			ret = __vb2_buf_mem_alloc(vb);
 			if (ret) {
 				dprintk(1, "failed allocating memory for "
@@ -400,6 +462,9 @@  static int __vb2_queue_alloc(struct vb2_queue *q, enum v4l2_memory memory,
 	if (memory == V4L2_MEMORY_MMAP)
 		__setup_offsets(q, buffer);
 
+	if (memory == V4L2_MEMORY_DMABUF)
+		__setup_dmabufs(q, buffer);
+
 	dprintk(1, "allocated %d buffers, %d plane(s) each\n",
 			buffer, num_planes);
 
@@ -859,7 +924,7 @@  static int __verify_memory_type(struct vb2_queue *q,
  *    to be used during streaming,
  * 4) allocates internal buffer structures (struct vb2_buffer), according to
  *    the agreed parameters,
- * 5) for MMAP memory type, allocates actual video memory, using the
+ * 5) for MMAP and DMABUF memory types, allocates actual video memory, using the
  *    memory handling/allocation routines provided during queue initialization
  *
  * If req->count is 0, all the memory will be freed instead.
@@ -885,7 +950,8 @@  static int __reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req)
 		 * are not in use and can be freed.
 		 */
 		mutex_lock(&q->mmap_lock);
-		if (q->memory == V4L2_MEMORY_MMAP && __buffers_in_use(q)) {
+		if ((q->memory == V4L2_MEMORY_MMAP ||
+		     q->memory == V4L2_MEMORY_DMABUF) && __buffers_in_use(q)) {
 			mutex_unlock(&q->mmap_lock);
 			dprintk(1, "memory in use, cannot free\n");
 			return -EBUSY;
@@ -1540,7 +1606,7 @@  static int __qbuf_dmabuf(struct vb2_buffer *vb, const struct v4l2_buffer *b)
 
 		/* Acquire each plane's memory */
 		mem_priv = call_ptr_memop(vb, attach_dmabuf, q->alloc_ctx[plane],
-			dbuf, planes[plane].length, dma_dir);
+			dbuf, planes[plane].length, dma_dir, NULL);
 		if (IS_ERR(mem_priv)) {
 			dprintk(1, "failed to attach dmabuf\n");
 			ret = PTR_ERR(mem_priv);
diff --git a/drivers/media/v4l2-core/videobuf2-dma-contig.c b/drivers/media/v4l2-core/videobuf2-dma-contig.c
index b481d20..8dc945e 100644
--- a/drivers/media/v4l2-core/videobuf2-dma-contig.c
+++ b/drivers/media/v4l2-core/videobuf2-dma-contig.c
@@ -793,7 +793,7 @@  static void vb2_dc_detach_dmabuf(void *mem_priv)
 	struct vb2_dc_buf *buf = mem_priv;
 
 	/* if vb2 works correctly you should never detach mapped buffer */
-	if (WARN_ON(buf->dma_addr))
+	if (WARN_ON(buf->dma_sgt))
 		vb2_dc_unmap_dmabuf(buf);
 
 	/* detach this attachment */
@@ -802,16 +802,18 @@  static void vb2_dc_detach_dmabuf(void *mem_priv)
 }
 
 static void *vb2_dc_attach_dmabuf(void *alloc_ctx, struct dma_buf *dbuf,
-	unsigned long size, enum dma_data_direction dma_dir)
+	unsigned long size, enum dma_data_direction dma_dir, void *buf_priv)
 {
 	struct vb2_dc_conf *conf = alloc_ctx;
-	struct vb2_dc_buf *buf;
+	struct vb2_dc_buf *buf = buf_priv;
 	struct dma_buf_attachment *dba;
 
 	if (dbuf->size < size)
 		return ERR_PTR(-EFAULT);
 
-	buf = kzalloc(sizeof(*buf), GFP_KERNEL);
+	if (!buf)
+		buf = kzalloc(sizeof(*buf), GFP_KERNEL);
+
 	if (!buf)
 		return ERR_PTR(-ENOMEM);
 
diff --git a/drivers/media/v4l2-core/videobuf2-dma-sg.c b/drivers/media/v4l2-core/videobuf2-dma-sg.c
index b1838ab..b9855fd 100644
--- a/drivers/media/v4l2-core/videobuf2-dma-sg.c
+++ b/drivers/media/v4l2-core/videobuf2-dma-sg.c
@@ -667,16 +667,18 @@  static void vb2_dma_sg_detach_dmabuf(void *mem_priv)
 }
 
 static void *vb2_dma_sg_attach_dmabuf(void *alloc_ctx, struct dma_buf *dbuf,
-	unsigned long size, enum dma_data_direction dma_dir)
+	unsigned long size, enum dma_data_direction dma_dir, void *buf_priv)
 {
 	struct vb2_dma_sg_conf *conf = alloc_ctx;
-	struct vb2_dma_sg_buf *buf;
+	struct vb2_dma_sg_buf *buf = buf_priv;
 	struct dma_buf_attachment *dba;
 
 	if (dbuf->size < size)
 		return ERR_PTR(-EFAULT);
 
-	buf = kzalloc(sizeof(*buf), GFP_KERNEL);
+	if (!buf)
+		buf = kzalloc(sizeof(*buf), GFP_KERNEL);
+
 	if (!buf)
 		return ERR_PTR(-ENOMEM);
 
diff --git a/drivers/media/v4l2-core/videobuf2-vmalloc.c b/drivers/media/v4l2-core/videobuf2-vmalloc.c
index bcde885..373294c 100644
--- a/drivers/media/v4l2-core/videobuf2-vmalloc.c
+++ b/drivers/media/v4l2-core/videobuf2-vmalloc.c
@@ -416,14 +416,16 @@  static void vb2_vmalloc_detach_dmabuf(void *mem_priv)
 }
 
 static void *vb2_vmalloc_attach_dmabuf(void *alloc_ctx, struct dma_buf *dbuf,
-	unsigned long size, enum dma_data_direction dma_dir)
+	unsigned long size, enum dma_data_direction dma_dir, void *buf_priv)
 {
-	struct vb2_vmalloc_buf *buf;
+	struct vb2_vmalloc_buf *buf = buf_priv;
 
 	if (dbuf->size < size)
 		return ERR_PTR(-EFAULT);
 
-	buf = kzalloc(sizeof(*buf), GFP_KERNEL);
+	if (!buf)
+		buf = kzalloc(sizeof(*buf), GFP_KERNEL);
+
 	if (!buf)
 		return ERR_PTR(-ENOMEM);
 
diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index a5790fd..374b26b 100644
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -49,6 +49,8 @@  struct vb2_threadio_data;
  *		   used for DMABUF memory types; alloc_ctx is the alloc context
  *		   dbuf is the shared dma_buf; returns NULL on failure;
  *		   allocator private per-buffer structure on success;
+ *		   if private per-buffer structure is provided reuse it
+ *		   instead of allocating a new one.
  *		   this needs to be used for further accesses to the buffer.
  * @detach_dmabuf: inform the exporter of the buffer that the current DMABUF
  *		   buffer is no longer used; the buf_priv argument is the
@@ -98,7 +100,8 @@  struct vb2_mem_ops {
 
 	void		*(*attach_dmabuf)(void *alloc_ctx, struct dma_buf *dbuf,
 					  unsigned long size,
-					  enum dma_data_direction dma_dir);
+					  enum dma_data_direction dma_dir,
+					  void *buf_priv);
 	void		(*detach_dmabuf)(void *buf_priv);
 	int		(*map_dmabuf)(void *buf_priv);
 	void		(*unmap_dmabuf)(void *buf_priv);