Hi Sakari, Thank you for your quick reply. > From: 'Sakari Ailus' [mailto:sakari.ailus@xxxxxx] > Sent: Tuesday, January 22, 2013 11:03 AM > Hi Kamil, > > (Cc'ing Pawel and Marek as well.) > > On Mon, Jan 21, 2013 at 03:07:55PM +0100, Kamil Debski wrote: > > Hi, > > > > > From: Sakari Ailus [mailto:sakari.ailus@xxxxxx] > > > Sent: Saturday, January 19, 2013 6:43 PM Hi Kamil, > > > > > > Thanks for the patch. > > > > > > On Mon, Jan 14, 2013 at 10:36:04AM +0100, Kamil Debski wrote: > > > > Set proper timestamp type in drivers that I am sure that use > > > > either MONOTONIC or COPY timestamps. Other drivers will correctly > > > > report UNKNOWN timestamp type instead of assuming that all > drivers > > > > use monotonic timestamps. > > > > > > What other kind of timestamps there can be? All drivers (at least > > > those not > > > mem-to-mem) that do obtain timestamps using system clock use > > > monotonic ones. > > > > Not set. It is not a COPY or MONOTONIC either. Any new or custom kind > > of timestamp, maybe? > > Then new timestamp types should be defined for the purpose. Which is > indeed what your patch is about. > > And about "COPY" timestamps: if an application wants to use timestamps, > it probably need to know what kind of timestamps they are. "COPY" > doesn't provide that information as such. Only the program that sets > the timestamps for the OUTPUT buffers does. For me the COPY type is clear. If the app gets a COPY timestamp on a buffer (CAPTURE) then it knows that it was copied from the OUTPUT buffer. If the application did not set the timestamp for OUTPUT buffer, then it has to cope with the consequences. > > > > I'd think that there should no longer be any drivers using the > > > UNKNOWN timestamp type: UNKNOWN is either from monotonic or > realtime > > > clock, and we just replaced all of them with the monotonic ones. No > > > driver uses realtime timestamps anymore. > > > > Maybe there should be no drivers using UNKNOWN. But definitely there > > should be no driver reporting MONOTONIC when the timestamp is not > > monotonic. > > > > > How about making MONOTONIC timestamps default instead, or at least > > > assigning all drivers something else than UNKNOWN? > > > > So why did you add the UNKNOWN flag? > > This is for API compatibility only. Applications running on kernels > prior to the headers of which define timestamp types will not have > timestamp type set (i.e. is zero, which equals to UNKNOWN). There was a > lengthy discussion on the topic back then, and the conclusion was that > the kernel version itself isn't enough to tell what kind of timestamps > are provided to the user. > > Any new driver shouldn't use UNKNOWN timestamps since in this case the > application would have to know what kind of timestamps the driver uses > --- which is why we now specify it in the API. > > > The way I see it - UNKNOWN is the default and the one who coded the > > driver will set it to either MONOTONIC or COPY if it is one of these > > two. It won't be changed otherwise. There are drivers, which do not > > fill the timestamp field at all: > > - drivers/media/platform/coda.c > > - drivers/media/platform/exynos-gsc/gsc-m2m.c > > - drivers/media/platform/m2m-deinterlace.c > > - drivers/media/platform/mx2_emmaprp.c > > - drivers/media/platform/s5p-fimc/fimc-m2m.c > > - drivers/media/platform/s5p-g2d.c > > - drivers/media/platform/s5p-jpeg/jpeg-core.c > > Excellent point. > > But --- should these drivers then fill the timestamp field? Isn't it a > bug in the driver not to do so? Could be. The only thing I am complaining about is that the type should not be reported as monotonic when it is not. (We can argue that constant is monotonic, but I think that it is not the point :-) ). This is why I propose to leave UNKNOWN as the default choice (which it is in case of non videobuf2 drivers). It is possible to eliminate the UNKNOWN in my opinion, but it should be up to the programmer to set the type. Another option is to eliminate the UNKNOWN flag in the next, or in two kernel releases. After the drivers are changed. Still I prefer to leave the driver's programmer in charge and leave the UNKNOWN type. > > > The way you did it in your patches left no room for any kind of > > choice. I did comment at least twice about mem-2-mem devices in your > > RFCs, if I remember correctly. I think Sylwester was also writing > > about this. > > Still everything got marked as MONOTONIC. > > I must have missed this in the discussion back then. > > > If we were to assume that there were no other timestamp types then > > monotonic (which is not true, but this was your assumption), then > what > > was the reason to add this timestamp framework? > > For capture devices whose video source has no native timestamps the > timestamps are MONOTONIC, at least until it is made selectable. Other > examples could include video decoders or encoders, but these timestamps > will be entirely different kind, and probably doesn't end up to the > timestamp field. > Thanks. Best wishes, -- Kamil Debski Linux Platform Group 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
