On Friday, April 08, 2011 09:00:55 Marek Szyprowski wrote:
> 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?
In the non-blocking case vb2_read will also return EAGAIN. Which is what
I meant. So nothing needs to be changed.
Regards,
Hans
>
> >
> > 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
>
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