On Fri September 14 2012 23:05:45 Sakari Ailus wrote: > Hi Rémi, > > Rémi Denis-Courmont wrote: > > Le vendredi 14 septembre 2012 23:25:01, Sakari Ailus a écrit : > >> I had a quick discussion with Laurent, and what he suggested was to use > >> the kernel version to figure out the type of the timestamp. The drivers > >> that use the monotonic time right now wouldn't be affected by the new > >> flag on older kernels. If we've decided we're going to switch to > >> monotonic time anyway, why not just change all the drivers now and > >> forget the capability flag. > > > > That does not work In Real Life. > > > > People do port old drivers forward to new kernels. > > People do port new drivers back to old kernels > > Why would you port a driver from an old kernel to a new kernel? Or are > you talking about out-of-tree drivers? More likely the latter. > If you do port drivers across different kernel versions I guess you're > supposed to use the appropriate interfaces for those kernels, too. Using > a helper function helps here, so compiling a backported driver would > fail w/o the helper function that produces the timestamp, forcing the > backporter to notice the situation. > > Anyway, I don't have a very strict opinion on this, so I'm okay with the > flag, too, but I personally simply don't think it's the best choice we > can make now. Also, without converting the drivers now the user space > must live with different kinds of timestamps much longer. There are a number of reasons why I want to go with a flag: - Out-of-tree drivers which are unlikely to switch to monotonic in practice - Backporting drivers - It makes it easy to verify in v4l2-compliance and enforce the use of the monotonic clock. - It's easy for apps to check. The third reason is probably the most important one for me. There tends to be a great deal of inertia before changes like this are applied to new drivers, and without being able to (easily) check this in v4l2-compliance more drivers will be merged that keep using gettimeofday. It's all too easy to miss in a review. That doesn't mean that it isn't a good idea to convert existing drivers asap. But it's not something I'm likely to take up myself. Creating a small helper function as you suggested elsewhere is a good idea as well. I'll write something for that. Regards, Hans -- 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
