On Thu, Aug 22, 2024 at 8:28 AM Laurent Pinchart
<laurent.pinchart@xxxxxxxxxxxxxxxx> wrote:
>
> Hi Benjamin,
>
> On Thu, Mar 14, 2024 at 04:32:19PM +0100, Benjamin Gaignard wrote:
> > Add 'min_reqbufs_allocation' field in the vb2_queue structure so drivers
> > can specify the minimum number of buffers to allocate when calling
> > VIDIOC_REQBUFS.
> > When initializing the queue, v4l2 core makes sure that the following
> > constraints are respected:
> > - the minimum number of buffers to allocate must be at least 2 because
> > one buffer is used by the hardware while the other is being processed
> > by userspace.
>
> This breaks userspace for the Renesas vsp1 driver :-( Unit tests fail,
> as some of them rely on operation with a single buffer.
>
> The vsp1 is a memory-to-memory processing engine, so operating with a
> single buffer is fine in some use cases. I would argue that for live
> capture devices there are valid use cases to operate with a single
> buffer too. Changing this by default will break use cases.
>
> How can we relax this check ? Should I simply submit a patch that lowers
> the minimum to one buffer ?
>
Uhm, I didn't notice this when reading this series. (Actually if I
recall correctly, originally it didn't have this restriction.)
Indeed, I don't see what's wrong with just having 1 buffer. If
performance is not a concern, it's okay to just serialize the
operation on 1 buffer.
If you would be so nice to send it, I think a patch that changes
min_reqbufs_allocation to max(max(1, min_reqbufs_allocation),
min_queued_buffers)) would be good.
That said, Benjamin, Hans, are we missing something by any chance? :)
Best,
Tomasz
> > -if the driver needs 'min_queued_buffers' in the queue before calling
> > start_streaming(), then the minimum requirement is 'min_queued_buffers + 1'
> > to keep at least one buffer available for userspace.
> >
> > Simplify __vb2_init_fileio() by using 'min_reqbufs_allocation' directly
> > to avoid duplicating the minimum number of buffers to allocate computation.
> >
> > Signed-off-by: Benjamin Gaignard <benjamin.gaignard@xxxxxxxxxxxxx>
> > ---
> > .../media/common/videobuf2/videobuf2-core.c | 38 +++++++++++--------
> > include/media/videobuf2-core.h | 15 +++++++-
> > 2 files changed, 37 insertions(+), 16 deletions(-)
> >
> > diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> > index d8b3c04cb3b5..58c495b253ce 100644
> > --- a/drivers/media/common/videobuf2/videobuf2-core.c
> > +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> > @@ -866,7 +866,7 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
> > /*
> > * Make sure the requested values and current defaults are sane.
> > */
> > - num_buffers = max_t(unsigned int, *count, q->min_queued_buffers);
> > + num_buffers = max_t(unsigned int, *count, q->min_reqbufs_allocation);
> > num_buffers = min_t(unsigned int, num_buffers, q->max_num_buffers);
> > memset(q->alloc_devs, 0, sizeof(q->alloc_devs));
> > /*
> > @@ -918,7 +918,7 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
> > * There is no point in continuing if we can't allocate the minimum
> > * number of buffers needed by this vb2_queue.
> > */
> > - if (allocated_buffers < q->min_queued_buffers)
> > + if (allocated_buffers < q->min_reqbufs_allocation)
> > ret = -ENOMEM;
> >
> > /*
> > @@ -2524,6 +2524,25 @@ int vb2_core_queue_init(struct vb2_queue *q)
> > if (WARN_ON(q->supports_requests && q->min_queued_buffers))
> > return -EINVAL;
> >
> > + /*
> > + * The minimum requirement is 2: one buffer is used
> > + * by the hardware while the other is being processed by userspace.
> > + */
> > + if (q->min_reqbufs_allocation < 2)
> > + q->min_reqbufs_allocation = 2;
> > +
> > + /*
> > + * If the driver needs 'min_queued_buffers' in the queue before
> > + * calling start_streaming() then the minimum requirement is
> > + * 'min_queued_buffers + 1' to keep at least one buffer available
> > + * for userspace.
> > + */
> > + if (q->min_reqbufs_allocation < q->min_queued_buffers + 1)
> > + q->min_reqbufs_allocation = q->min_queued_buffers + 1;
> > +
> > + if (WARN_ON(q->min_reqbufs_allocation > q->max_num_buffers))
> > + return -EINVAL;
> > +
> > INIT_LIST_HEAD(&q->queued_list);
> > INIT_LIST_HEAD(&q->done_list);
> > spin_lock_init(&q->done_lock);
> > @@ -2717,7 +2736,6 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read)
> > struct vb2_fileio_data *fileio;
> > struct vb2_buffer *vb;
> > int i, ret;
> > - unsigned int count = 0;
> >
> > /*
> > * Sanity check
> > @@ -2738,18 +2756,8 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read)
> > if (q->streaming || vb2_get_num_buffers(q) > 0)
> > return -EBUSY;
> >
> > - /*
> > - * Start with q->min_queued_buffers + 1, driver can increase it in
> > - * queue_setup()
> > - *
> > - * 'min_queued_buffers' buffers need to be queued up before you
> > - * can start streaming, plus 1 for userspace (or in this case,
> > - * kernelspace) processing.
> > - */
> > - count = max(2, q->min_queued_buffers + 1);
> > -
> > dprintk(q, 3, "setting up file io: mode %s, count %d, read_once %d, write_immediately %d\n",
> > - (read) ? "read" : "write", count, q->fileio_read_once,
> > + (read) ? "read" : "write", q->min_reqbufs_allocation, q->fileio_read_once,
> > q->fileio_write_immediately);
> >
> > fileio = kzalloc(sizeof(*fileio), GFP_KERNEL);
> > @@ -2763,7 +2771,7 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read)
> > * Request buffers and use MMAP type to force driver
> > * to allocate buffers by itself.
> > */
> > - fileio->count = count;
> > + fileio->count = q->min_reqbufs_allocation;
> > fileio->memory = VB2_MEMORY_MMAP;
> > fileio->type = q->type;
> > q->fileio = fileio;
> > diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> > index 667bf9ee1101..4a8b9135cec8 100644
> > --- a/include/media/videobuf2-core.h
> > +++ b/include/media/videobuf2-core.h
> > @@ -549,9 +549,21 @@ struct vb2_buf_ops {
> > * @start_streaming can be called. Used when a DMA engine
> > * cannot be started unless at least this number of buffers
> > * have been queued into the driver.
> > - * VIDIOC_REQBUFS will ensure at least @min_queued_buffers
> > + * VIDIOC_REQBUFS will ensure at least @min_queued_buffers + 1
> > * buffers will be allocated. Note that VIDIOC_CREATE_BUFS will not
> > * modify the requested buffer count.
> > + * @min_reqbufs_allocation: the minimum number of buffers to be allocated when
> > + * calling VIDIOC_REQBUFS. Note that VIDIOC_CREATE_BUFS will *not*
> > + * modify the requested buffer count and does not use this field.
> > + * Drivers can set this if there has to be a certain number of
> > + * buffers available for the hardware to work effectively.
> > + * This allows calling VIDIOC_REQBUFS with a buffer count of 1 and
> > + * it will be automatically adjusted to a workable buffer count.
> > + * If set, then @min_reqbufs_allocation must be larger than
> > + * @min_queued_buffers + 1.
> > + * If this field is > 3, then it is highly recommended that the
> > + * driver implements the V4L2_CID_MIN_BUFFERS_FOR_CAPTURE/OUTPUT
> > + * control.
> > * @alloc_devs: &struct device memory type/allocator-specific per-plane device
> > */
> > /*
> > @@ -622,6 +634,7 @@ struct vb2_queue {
> > u32 timestamp_flags;
> > gfp_t gfp_flags;
> > u32 min_queued_buffers;
> > + u32 min_reqbufs_allocation;
> >
> > struct device *alloc_devs[VB2_MAX_PLANES];
> >
>
> --
> Regards,
>
> Laurent Pinchart
