On 09/22/2012 10:28 PM, Daniel Glöckner wrote: > On Sat, Sep 22, 2012 at 07:12:52PM +0200, Sylwester Nawrocki wrote: >> If we ever need the clock selection API I would vote for an IOCTL. >> The controls API is a bad choice for something such fundamental as >> type of clock for buffer timestamping IMHO. Let's stop making the >> controls API a dumping ground for almost everything in V4L2! ;) > >> Perhaps VIDIOC_QUERYBUF and VIDIOC_DQBUF should be reporting >> timestamps type only for the time they are being called. Not per buffer, >> per device. And applications would be checking the flags any time they >> want to find out what is the buffer timestamp type. Or every time if it >> don't have full control over the device (S/G_PRIORITY). > > I'm all for adding an IOCTL, but if we think about adding a > VIDIOC_S_TIMESTAMP_TYPE in the future, we might as well add a > VIDIOC_G_TIMESTAMP_TYPE right now. Old drivers will return ENOSYS, > so the application knows it will have to guess the type (or take own > timestamps). Hmm, would it make sense to design a single ioctl that would allow getting and setting the clock type, e.g. VIDIOC_CLOCK/TIMESTAMP_TYPE ? > I can't imagine anything useful coming from an app that has to process > timestamps that change their source every now and then and I seriously > doubt anyone will go to such an extent that they check the timestamp > type on every buffer. If they don't set their priority high enough to > prevent others from changing the timestamp type, they also run the > risk of someone else changing the image format. It should be enough to > forbid changing the timestamp type while I/O is in progress, as it is > done for VIDIOC_S_FMT. I agree, but mem-to-mem devices can have multiple logically independent, "concurrent" streams active. If the clock type is per device it might not be that straightforward... Regards, Sylwester -- 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
