Re: [PATCH/RFC v2 2/2] v4l: vb2: Add fatal error condition flag

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Pawel,

On Friday 06 June 2014 14:31:15 Pawel Osciak wrote:
> Hi Laurent,
> Thanks for the patch. Did you test this to work in fileio mode? Looks
> like it should, but would like to make sure.

No, I haven't tested it. The OMAP4 ISS driver, which is my test target for 
this patch, doesn't support fileio mode. Adding VB2_READ would be easy, but 
the driver requires configuring the format on the file handle used for 
streaming, so I can't just run cat /dev/video*.

> On Thu, Jun 5, 2014 at 9:23 PM, Laurent Pinchart wrote:
> > When a fatal error occurs that render the device unusable, the only
> > options for a driver to signal the error condition to userspace is to
> > set the V4L2_BUF_FLAG_ERROR flag when dequeuing buffers and to return an
> > error from the buffer prepare handler when queuing buffers.
> > 
> > The buffer error flag indicates a transient error and can't be used by
> > applications to detect fatal errors. Returning an error from vb2_qbuf()
> > is thus the only real indication that a fatal error occurred. However,
> > this is difficult to handle for multithreaded applications that requeue
> > buffers from a thread other than the control thread. In particular the
> > poll() call in the control thread will not notify userspace of the
> > error.
> > 
> > This patch adds an explicit mechanism to report fatal errors to
> > userspace. Applications can call the vb2_queue_error() function to
> > signal a fatal error. From this moment on, buffer preparation will
> > return -EIO to userspace, and vb2_poll() will set the POLLERR flag and
> > return immediately. The error flag is cleared when cancelling the queue,
> > either at stream off time (through vb2_streamoff) or when releasing the
> > queue with vb2_queue_release().
> > 
> > Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

-- 
Regards,

Laurent Pinchart