Hello,
On Monday, April 04, 2011 1:52 PM Hans Verkuil wrote:
> The vb2_poll function would start read DMA if called without any streaming
> in progress. This unfortunately does not work if the application just wants
> to poll for exceptions. This information of what the application is polling
> for is sadly unavailable in the driver.
>
> Andy Walls suggested to just return POLLIN | POLLRDNORM and let the first
> call to read start the DMA. This initial read() call will return EAGAIN
> since no actual data is available yet, but it does start the DMA.
The current implementation of vb2_read() will just start streaming on first
call without returning EAGAIN. Do you think this should be changed?
>
> Application are supposed to handle EAGAIN. MythTV does handle this
> correctly.
>
> Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
> ---
> drivers/media/video/videobuf2-core.c | 16 +++-------------
> 1 files changed, 3 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/media/video/videobuf2-core.c
> b/drivers/media/video/videobuf2-core.c
> index 6698c77..2dea57a 100644
> --- a/drivers/media/video/videobuf2-core.c
> +++ b/drivers/media/video/videobuf2-core.c
> @@ -1372,20 +1372,10 @@ unsigned int vb2_poll(struct vb2_queue *q, struct
> file *file, poll_table *wait)
> * Start file I/O emulator only if streaming API has not been used
> yet.
> */
> if (q->num_buffers == 0 && q->fileio == NULL) {
> - if (!V4L2_TYPE_IS_OUTPUT(q->type) && (q->io_modes & VB2_READ))
> {
> - ret = __vb2_init_fileio(q, 1);
> - if (ret)
> - return POLLERR;
> - }
> - if (V4L2_TYPE_IS_OUTPUT(q->type) && (q->io_modes & VB2_WRITE))
> {
> - ret = __vb2_init_fileio(q, 0);
> - if (ret)
> - return POLLERR;
> - /*
> - * Write to OUTPUT queue can be done immediately.
> - */
> + if (!V4L2_TYPE_IS_OUTPUT(q->type) && (q->io_modes & VB2_READ))
> + return POLLIN | POLLRDNORM;
> + if (V4L2_TYPE_IS_OUTPUT(q->type) && (q->io_modes & VB2_WRITE))
> return POLLOUT | POLLWRNORM;
> - }
> }
>
> /*
> --
Best regards
--
Marek Szyprowski
Samsung Poland R&D Center
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