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

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