Hi Laurent,
On Mon, Feb 11, 2013 at 08:42:37PM +0100, Laurent Pinchart wrote:
> Hi Michael,
>
> On Monday 04 February 2013 11:58:27 Michael Grzeschik wrote:
> > On Thu, Jan 17, 2013 at 04:23:51PM +0530, Bhupesh Sharma wrote:
> > > This patch reworks the videobuffer management logic present in the UVC
> > > webcam gadget and ports it to use the "more apt" videobuf2 framework for
> > > video buffer management.
> > >
> > > To support routing video data captured from a real V4L2 video capture
> > > device with a "zero copy" operation on videobuffers (as they pass from
> > > the V4L2 domain to UVC domain via a user-space application), we need to
> > > support USER_PTR IO method at the UVC gadget side.
> > >
> > > So the V4L2 capture device driver can still continue to use MMAP IO
> > > method and now the user-space application can just pass a pointer to the
> > > video buffers being dequeued from the V4L2 device side while queueing
> > > them at the UVC gadget end. This ensures that we have a "zero-copy"
> > > design as the videobuffers pass from the V4L2 capture device to the UVC
> > > gadget.
> > >
> > > Note that there will still be a need to apply UVC specific payload
> > > headers on top of each UVC payload data, which will still require a copy
> > > operation to be performed in the 'encode' routines of the UVC gadget.
> > >
> > > This patch also addresses one issue found out while porting the UVC
> > > gadget to videobuf2 framework:
> > > - In case the usb requests queued by the gadget get completed
> > > with a status of -ESHUTDOWN (disconnected from host),
> > > the queue of videobuf2 should be cancelled to ensure that the
> > > application space daemon is not left in a state waiting for
> > > a vb2 to be successfully absorbed at the USB side.
> > >
> > > Signed-off-by: Bhupesh Sharma <bhupesh.sharma@xxxxxx>
> > > ---
> > >
> > > drivers/usb/gadget/Kconfig | 1 +
> > > drivers/usb/gadget/uvc_queue.c | 537 +++++++++++------------------------
> > > drivers/usb/gadget/uvc_queue.h | 25 +--
> > > drivers/usb/gadget/uvc_v4l2.c | 27 +--
> > > drivers/usb/gadget/uvc_video.c | 18 +-
> > > 5 files changed, 189 insertions(+), 419 deletions(-)
>
> [snip]
>
> > > diff --git a/drivers/usb/gadget/uvc_queue.c
> > > b/drivers/usb/gadget/uvc_queue.c index 104ae9c..bd20fab 100644
> > > --- a/drivers/usb/gadget/uvc_queue.c
> > > +++ b/drivers/usb/gadget/uvc_queue.c
>
> [snip]
>
> > > -static int uvc_queue_waiton(struct uvc_buffer *buf, int nonblocking)
> > > +static int uvc_queue_buffer(struct uvc_video_queue *queue,
> > > + struct v4l2_buffer *buf)
> > > {
> > > - if (nonblocking) {
> > > - return (buf->state != UVC_BUF_STATE_QUEUED &&
> > > - buf->state != UVC_BUF_STATE_ACTIVE)
> > > - ? 0 : -EAGAIN;
> > > - }
> > > + int ret;
> > >
> > > - return wait_event_interruptible(buf->wait,
> > > - buf->state != UVC_BUF_STATE_QUEUED &&
> > > - buf->state != UVC_BUF_STATE_ACTIVE);
> > > + mutex_lock(&queue->mutex);
> > > + ret = vb2_qbuf(&queue->queue, buf);
> > > + mutex_unlock(&queue->mutex);
> > > +
> >
> > How is the UVC_QUEUE_PAUSED handling supposed to be handled here?
> > I see that this patch lost this hunk from uvc_queue_buffer():
> >
> > ret |= (queue->flags & uvc_queue_paused) != 0;
> > queue->flags &= ~UVC_QUEUE_PAUSED;
>
> Good catch. This needs to be handled. The PAUSED flag needs to be set with the
> irqlock held, this could be done in uvc_buffer_queue(). The return value needs
> to be computed when setting the flag, so it would need to be stored in the
> queue structure and read here. Adding a new UVC_QUEUE_PUMP flag should do but
> will require taking the irqlock again to read and clear that flag here. A new
> field is another possible solution.
the handling of UVC_QUEUE_PAUSED is currently implemented like this:
ret = (queue->flags & UVC_QUEUE_PAUSED) != 0
queue->flags &= ~UVC_QUEUE_PAUSED;
which is wrong as it overwrites the return value of vb2_qbuf
which will lead to an stalled connection if the return value
would be negative and got overwritten to "1".
What do you mean with the extra flag UVC_QUEUE_PUMP. I would like
to implement a fixup patch, but need more information how to
correctly handle the extra return value here.
Thanks,
Michael
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