On Monday 21 September 2009 19:23:54 Sakari Ailus wrote: > Hans Verkuil wrote: > > On Sunday 13 September 2009 08:13:04 Nathaniel Kim wrote: > >> 2009. 9. 12., 오전 7:21, Hans Verkuil 작성: > >> > >> Hans, > >> > >> First of all I'm very sorry that I had not enough time to go through > >> your new RFC. I'll checkout right after posting this mail. > >> > >> I think this is a good approach and I also had in my mind that sysfs > >> might be a good method if we could control and monitor through this. > >> Recalling memory when we had a talk in San Francisco, I was frustrated > >> that there is no way to catch events from sort of sub-devices like > >> lens actuator (I mean pizeo motors in camera module). As you know lens > >> actuator is an extremely slow device in comparison with common v4l2 > >> devices we are using and we need to know whether it has succeeded or > >> not in moving to expected position. > >> So I considered sysfs and udev as candidates for catching events from > >> sub-devices. events like success/failure of lens movement, change of > >> status of subdevices. > >> Does anybody experiencing same issue? I think I've seen a lens > >> controller driver in omap3 kernel from TI but not sure how did they > >> control that. > >> > >> My point is that we need a kind of framework to give and event to user > >> space and catching them properly just like udev does. > > > > When I was talking to Laurent Pinchart and Sakari and his team at Nokia > > we discussed just such a framework. It actually exists already, although > > it is poorly implemented. > > > > Look at include/linux/dvb/video.h, struct video_event and ioctl > > VIDEO_GET_EVENT. It is used in ivtv (ivtv-ioctl.c, look for > > VIDEO_GET_EVENT). > > > > The idea is that you can either call VIDEO_GET_EVENT to wait for an event > > or use select() and wait for an exception to arrive, and then call > > VIDEO_GET_EVENT to find which event it was. > > > > This is ideal for streaming-related events. In ivtv it is used to report > > VSYNCs and to report when the MPEG decoder stopped (there is a delay > > between stopping sending new data to the decoder and when it actually > > processed all its internal buffers). > > > > Laurent is going to look into this to clean it up and present it as a new > > proper official V4L2 event mechanism. > > > > For events completely specific to a subdev I wonder whether it wouldn't > > be a good idea to use the media controller device for that. I like the > > select() mechanism since in an application you can just select() on a > > whole bunch of filehandles. If you can't use select() then you are forced > > to do awkward coding (e.g. make a separate thread just to handle that > > other event mechanism). > > Agree. There's no reasonable way to use video devices here since the > events may be connected to non-video related issues --- like the > statistics. > > One possible approach could be allocating a device node for each subdev > and use them and leave the media controller device with just the media > controller specific ioctls. Then there would be no need to set current > subdev nor bind the subdev to file handle either. > > Just an idea. > > > So with the media controller we can easily let sub-devices notify the > > media controller when an event is ready and the media controller can then > > generate an exception. An application can just select() on the mc > > filehandle. > > > > There are two ways of implementing this. One is that the media controller > > keeps a global queue of pending events and subdevices just queue events > > to that when they arrive (with some queue size limit to prevent run-away > > events). > > With the above arrangement, the events could be easily subdev specific. > The mechanism should be generic still, though. > > > So when you call some GET_EVENT type ioctl it should return the ID of the > > subdevice (aka entity) as well. What makes me slightly uncomfortable is > > that you still want to use that same ioctl on a normal video node. And > > the subdev ID has really no meaning there. But making two different > > ioctls doesn't sit well with me either. > > > > The alternative implementation is that the mc will only wait for events > > from the currently selected sub-device. So if you want to wait on events > > from different sub-devices, then you have to open the mc multiple times, > > once for each subdev that you want to receive events from. > > > > I think I would probably go for the second implementation because it is > > consistent with the way ioctls are passed to sub-devices. I like the idea > > that you can just pass regular V4L2 ioctls to sub-devices. Not all ioctls > > make sense, obviously (e.g. any of the streaming I/O ioctls), but a > > surprisingly large number of ioctls can be used in that way. > > I agree with this. There are just a few ioctls that probably don't make > sense (e.g. the steaming related ones). > > IMO even the format setting ioctls could be nice since the possible > input and output formats of the subdevs should be enumerable, too. > > ENUM_FRAMESIZES and ENUM_FRAMEINTERVALS are missing the v4l2_buf_type, > but there are reserved fields... Those two ioctls are still marked as experimental. Does that mean we could change them in an ABI incompatible way ? -- 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
