On 04/25/2016 09:59 AM, Ricardo Ribalda Delgado wrote:
> When using a device is read/write mode, vb2 does not handle properly the
> first select/poll operation.
>
> The reason for this, is that when this code has been refactored, some of
> the operations have changed their order, and now fileio emulator is not
> started.
>
> The reintroduced check to the core is enabled by a quirk flag, that
> avoids this check by other subsystems like DVB.
>
> Reported-by: Dimitrios Katsaros <patcherwork@xxxxxxxxx>
> Cc: Junghak Sung <jh1009.sung@xxxxxxxxxxx>
> Fixes: 49d8ab9feaf2 ("media] media: videobuf2: Separate vb2_poll()")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@xxxxxxxxx>
> ---
>
> v2: By Hans Verkuil <hverkuil@xxxxxxxxx> and
> Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxx>:
>
> Add a quirk bit to enable this behaviour on the core.
> drivers/media/v4l2-core/videobuf2-core.c | 9 +++++++++
> drivers/media/v4l2-core/videobuf2-v4l2.c | 9 +--------
> include/media/videobuf2-core.h | 4 ++++
> 3 files changed, 14 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
> index 5d016f496e0e..58eb9be13510 100644
> --- a/drivers/media/v4l2-core/videobuf2-core.c
> +++ b/drivers/media/v4l2-core/videobuf2-core.c
> @@ -2298,6 +2298,15 @@ unsigned int vb2_core_poll(struct vb2_queue *q, struct file *file,
> return POLLERR;
>
> /*
> + * For compatibility with vb1: if QBUF hasn't been called yet, then
> + * return POLLERR as well. This only affects capture queues, output
> + * queues will always initialize waiting_for_buffers to false.
> + */
This comment should be moved to where the quirk is set in v4l2. This comment shouldn't
refer to vb2 at all. How about:
"If this quirk is set and if QBUF hasn't been called..."
and perhaps at the end of the comment:
"This quirk is set by V4L2 for backwards compatibility reasons."
although I am not completely certain we need that at all here.
> + if (q->quirk_poll_must_check_waiting_for_buffers &&
> + q->waiting_for_buffers && (req_events & (POLLIN | POLLRDNORM)))
> + return POLLERR;
> +
> + /*
> * For output streams you can call write() as long as there are fewer
> * buffers queued than there are buffers available.
> */
> diff --git a/drivers/media/v4l2-core/videobuf2-v4l2.c b/drivers/media/v4l2-core/videobuf2-v4l2.c
> index 91f552124050..3e649adf85ef 100644
> --- a/drivers/media/v4l2-core/videobuf2-v4l2.c
> +++ b/drivers/media/v4l2-core/videobuf2-v4l2.c
> @@ -765,6 +765,7 @@ int vb2_queue_init(struct vb2_queue *q)
> q->is_output = V4L2_TYPE_IS_OUTPUT(q->type);
> q->copy_timestamp = (q->timestamp_flags & V4L2_BUF_FLAG_TIMESTAMP_MASK)
> == V4L2_BUF_FLAG_TIMESTAMP_COPY;
> + q->quirk_poll_must_check_waiting_for_buffers = true;
>
> return vb2_core_queue_init(q);
> }
> @@ -818,14 +819,6 @@ unsigned int vb2_poll(struct vb2_queue *q, struct file *file, poll_table *wait)
> poll_wait(file, &fh->wait, wait);
> }
>
> - /*
> - * For compatibility with vb1: if QBUF hasn't been called yet, then
> - * return POLLERR as well. This only affects capture queues, output
> - * queues will always initialize waiting_for_buffers to false.
> - */
> - if (q->waiting_for_buffers && (req_events & (POLLIN | POLLRDNORM)))
> - return POLLERR;
> -
> return res | vb2_core_poll(q, file, wait);
> }
> EXPORT_SYMBOL_GPL(vb2_poll);
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index 8a0f55b6c2ba..3a1620946068 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -400,6 +400,9 @@ struct vb2_buf_ops {
> * @fileio_read_once: report EOF after reading the first buffer
> * @fileio_write_immediately: queue buffer after each write() call
> * @allow_zero_bytesused: allow bytesused == 0 to be passed to the driver
> + * @quirk_poll_must_check_waiting_for_buffers: Return POLLERR at poll when QBUF
> + * has not been called. This is a vb1 idiom that has been adopted
> + * also by vb2.
> * @lock: pointer to a mutex that protects the vb2_queue struct. The
> * driver can set this to a mutex to let the v4l2 core serialize
> * the queuing ioctls. If the driver wants to handle locking
> @@ -463,6 +466,7 @@ struct vb2_queue {
> unsigned fileio_read_once:1;
> unsigned fileio_write_immediately:1;
> unsigned allow_zero_bytesused:1;
> + unsigned quirk_poll_must_check_waiting_for_buffers:1;
>
> struct mutex *lock;
> void *owner;
>
Regards,
Hans
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