On Saturday 26 February 2011 14:03:53 Guennadi Liakhovetski wrote: > On Sat, 26 Feb 2011, Hans Verkuil wrote: > > On Friday, February 25, 2011 18:08:07 Guennadi Liakhovetski wrote: > > > > <snip> > > > > > > > configure the sensor to react on an external trigger provided by > > > > > the flash controller is needed, and that could be a control on the > > > > > flash sub-device. What we would probably miss is a way to issue a > > > > > STREAMON with a number of frames to capture. A new ioctl is > > > > > probably needed there. Maybe that would be an opportunity to > > > > > create a new stream-control ioctl that could replace STREAMON and > > > > > STREAMOFF in the long term (we could extend the subdev s_stream > > > > > operation, and easily map STREAMON and STREAMOFF to the new ioctl > > > > > in video_ioctl2 internally). > > > > > > > > How would this be different from queueing n frames (in total; count > > > > dequeueing, too) and issuing streamon? --- Except that when the last > > > > frame is processed the pipeline could be stopped already before > > > > issuing STREAMOFF. That does indeed have some benefits. Something > > > > else? > > > > > > Well, you usually see in your host driver, that the videobuffer queue > > > is empty (no more free buffers are available), so, you stop streaming > > > immediately too. > > > > This probably assumes that the host driver knows that this is a special > > queue? Because in general drivers will simply keep capturing in the last > > buffer and not release it to userspace until a new buffer is queued. > > Yes, I know about this spec requirement, but I also know, that not all > drivers do that and not everyone is happy about that requirement:) Is it a requirement, or just something some drivers do ? Several drivers just stop capturing when no buffer is available, and resume when a new buffer is queued. > > That said, it wouldn't be hard to add some flag somewhere that puts a > > queue in a 'stop streaming on last buffer capture' mode. > > No, it wouldn't... But TBH this doesn't seem like the most elegant and > complete solution. Maybe we have to think a bit more about it - which > soncequences switching into the snapshot mode has on the host driver, > apart from stopping after N frames. So, this is one of the possibilities, > not sure if the best one. -- Regards, Laurent Pinchart -- 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
