VIDIOC_STREAMON expects buffers to be queued before hardware part of image/video pipe is enabled. From my experience of V4L2 user space, I have always QBUFfed before invoking the STREAMON. Below is the API specification which also speaks something same: http://linuxtv.org/downloads/v4l-dvb-apis/vidioc-streamon.html I think its better to return EINVAL if there are no queued buffers when VIDIOC_STREAMON is invoked. Regards, Subash On Mon, Mar 14, 2011 at 3:44 PM, Sylwester Nawrocki <s.nawrocki@xxxxxxxxxxx> wrote: > Hello, > > As far as I know V4L2 applications are allowed to call VIDIOC_STREAMON before > queuing buffers with VIDIOC_QBUF. > > This leads to situation that a H/W is attempted to be enabled by the driver > when it has no any buffer ownership. > > Effectively actual activation of the data pipeline has to be deferred > until first buffer arrived in the driver. Which makes it difficult > to signal any errors to user during enabling the data pipeline. > > Is this allowed to force applications to queue some buffers before calling > STREAMON, by returning an error in vidioc_streamon from the driver, when > no buffers have been queued at this time? > > I suppose this could render some applications to stop working if this kind > of restriction is applied e.g. in camera capture driver. > > What the applications really expect? > > With the above I refer mostly to a snapshot mode where we have to be careful > not to lose any frame, as there could be only one.. > > > Please share you opinions. > > > Regards, > -- > Sylwester Nawrocki > Samsung Poland R&D Center > -- > To unsubscribe from this list: send the line "unsubscribe linux-media" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
