Re: [PATCH 03/14] media: videobuf2: Allow exporting of a struct dmabuf

Laurent Pinchart
2022-11-21T23:18:18Z

Hi Umang and Dave,

Thank you for the patch.

On Tue, Nov 22, 2022 at 03:17:11AM +0530, Umang Jain wrote:
> From: Dave Stevenson <dave.stevenson@raspberrypi.org>
>
> videobuf2 only allowed exporting a dmabuf as a file descriptor,
> but there are instances where having the struct dma_buf is
> useful within the kernel.
>
> Split the current implementation into two, one step which
> exports a struct dma_buf, and the second which converts that
> into an fd.
>
> Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.org>
> Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
> ---
> .../media/common/videobuf2/videobuf2-core.c | 36 +++++++++++++------
> include/media/videobuf2-core.h | 15 ++++++++
> 2 files changed, 40 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> index ab9697f3b5f1..32b26737cac4 100644
> --- a/drivers/media/common/videobuf2/videobuf2-core.c
> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> @@ -2184,49 +2184,49 @@ static int __find_plane_by_offset(struct vb2_queue *q, unsigned long off,
> return -EINVAL;
> }
>
> -int vb2_core_expbuf(struct vb2_queue *q, int *fd, unsigned int type,
> - unsigned int index, unsigned int plane, unsigned int flags)
> +struct dma_buf *vb2_core_expbuf_dmabuf(struct vb2_queue *q, unsigned int type,
> + unsigned int index, unsigned int plane,
> + unsigned int flags)

This function is used in the ISP driver, in bcm2835_isp_buf_prepare(),
for MMAP buffers, and as far as I can tell, its only purpose is to
create a dma_buf instance to then be imported in
vchiq_mmal_submit_buffer() with a call to vc_sm_cma_import_dmabuf().
That sounds like a very complicated set of operations, and quite
inefficient :-(

> {
> struct vb2_buffer *vb = NULL;
> struct vb2_plane *vb_plane;
> - int ret;
> struct dma_buf *dbuf;
>
> if (q->memory != VB2_MEMORY_MMAP) {
> dprintk(q, 1, "queue is not currently set up for mmap\n");
> - return -EINVAL;
> + return ERR_PTR(-EINVAL);
> }
>
> if (!q->mem_ops->get_dmabuf) {
> dprintk(q, 1, "queue does not support DMA buffer exporting\n");
> - return -EINVAL;
> + return ERR_PTR(-EINVAL);
> }
>
> if (flags & ~(O_CLOEXEC | O_ACCMODE)) {
> dprintk(q, 1, "queue does support only O_CLOEXEC and access mode flags\n");
> - return -EINVAL;
> + return ERR_PTR(-EINVAL);
> }
>
> if (type != q->type) {
> dprintk(q, 1, "invalid buffer type\n");
> - return -EINVAL;
> + return ERR_PTR(-EINVAL);
> }
>
> if (index >= q->num_buffers) {
> dprintk(q, 1, "buffer index out of range\n");
> - return -EINVAL;
> + return ERR_PTR(-EINVAL);
> }
>
> vb = q->bufs[index];
>
> if (plane >= vb->num_planes) {
> dprintk(q, 1, "buffer plane out of range\n");
> - return -EINVAL;
> + return ERR_PTR(-EINVAL);
> }
>
> if (vb2_fileio_is_active(q)) {
> dprintk(q, 1, "expbuf: file io in progress\n");
> - return -EBUSY;
> + return ERR_PTR(-EBUSY);
> }
>
> vb_plane = &vb->planes[plane];
> @@ -2238,9 +2238,23 @@ int vb2_core_expbuf(struct vb2_queue *q, int *fd, unsigned int type,
> if (IS_ERR_OR_NULL(dbuf)) {
> dprintk(q, 1, "failed to export buffer %d, plane %d\n",
> index, plane);
> - return -EINVAL;
> + return ERR_PTR(-EINVAL);
> }
>
> + return dbuf;
> +}
> +EXPORT_SYMBOL_GPL(vb2_core_expbuf_dmabuf);
> +
> +int vb2_core_expbuf(struct vb2_queue *q, int *fd, unsigned int type,
> + unsigned int index, unsigned int plane, unsigned int flags)
> +{
> + struct dma_buf *dbuf;
> + int ret;
> +
> + dbuf = vb2_core_expbuf_dmabuf(q, type, index, plane, flags);
> + if (IS_ERR(dbuf))
> + return PTR_ERR(dbuf);
> +
> ret = dma_buf_fd(dbuf, flags & ~O_ACCMODE);
> if (ret < 0) {
> dprintk(q, 3, "buffer %d, plane %d failed to export (%d)\n",
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index 3253bd2f6fee..33629ed2b64f 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -911,6 +911,21 @@ int vb2_core_streamon(struct vb2_queue *q, unsigned int type);
> */
> int vb2_core_streamoff(struct vb2_queue *q, unsigned int type);
>
> +/**
> + * vb2_core_expbuf_dmabuf() - Export a buffer as a dma_buf structure
> + * @q: videobuf2 queue
> + * @type: buffer type
> + * @index: id number of the buffer
> + * @plane: index of the plane to be exported, 0 for single plane queues
> + * @flags: flags for newly created file, currently only O_CLOEXEC is
> + * supported, refer to manual of open syscall for more details
> + *
> + * Return: Returns the dmabuf pointer
> + */
> +struct dma_buf *vb2_core_expbuf_dmabuf(struct vb2_queue *q, unsigned int type,
> + unsigned int index, unsigned int plane,
> + unsigned int flags);
> +
> /**
> * vb2_core_expbuf() - Export a buffer as a file descriptor.
> * @q: pointer to &struct vb2_queue with videobuf2 queue.

--
Regards,

Laurent Pinchart