On 08/31/2013 10:36 PM, Guennadi Liakhovetski wrote: > On Sat, 31 Aug 2013, Laurent Pinchart wrote: > >> Hi Guennadi, >> >> On Saturday 31 August 2013 20:38:54 Guennadi Liakhovetski wrote: >>> On Sat, 31 Aug 2013, Hans Verkuil wrote: >>>> On 08/30/2013 03:01 PM, Hans Verkuil wrote: >>>>> OK, I know, we don't even know yet when the mini-summit will be held but >>>>> I thought I'd just start this thread to collect input for the agenda. >>>>> >>>>> I have these topics (and I *know* that I am forgetting a few): >> >> [snip] >> >>>>> Feel free to add suggestions to this list. >>>> >>>> I got another one: >>>> >>>> VIDIOC_TRY_FMT shouldn't return -EINVAL when an unsupported pixelformat is >>>> provided, but in practice video capture board tend to do that, while >>>> webcam drivers tend to map it silently to a valid pixelformat. Some >>>> applications rely on the -EINVAL error code. >>>> >>>> We need to decide how to adjust the spec. I propose to just say that some >>>> drivers will map it silently and others will return -EINVAL and that you >>>> don't know what a driver will do. Also specify that an unsupported >>>> pixelformat is the only reason why TRY_FMT might return -EINVAL. >>>> >>>> Alternatively we might want to specify explicitly that EINVAL should be >>>> returned for video capture devices (i.e. devices supporting S_STD or >>>> S_DV_TIMINGS) and 0 for all others. >>> >>> Just to make sure I understand right - that kind of excludes cameras, >>> right? Still, even for (other) video capture devices, like TV decoders, is >>> there a real serious enough reason to _change_ the specs, which says >>> >>> http://linuxtv.org/downloads/v4l-dvb-apis/vidioc-g-fmt.html >>> >>> EINVAL >>> >>> The struct v4l2_format type field is invalid or the requested buffer >>> type not supported. >> >> I think Hans meant unsupported fmt.pix.pixelformat (or the equivalent for >> multiplane) values. > > Good, then I understood him correctly :) > >> For instance the uvcvideo driver will return a default >> fourcc if an application tries an unsupported fourcc, > > Yes, that's what I would do too and that's what the spec dictates. > >> some other drivers >> return -EINVAL. > > that just seems plain wrong to me. So, as I said, to not break the > userspace we can extend the specs, but not prohibit the currently defined > behaviour. So, that last option: > >>>> Alternatively we might want to specify explicitly that EINVAL should be >>>> returned for video capture devices (i.e. devices supporting S_STD or >>>> S_DV_TIMINGS) and 0 for all others. > > I'm not sure I like a lot, unless those drivers are very special and they > all already behave like that. Almost (have to check though) all TV capture drivers behave like that, yes. Very unfortunate. On the other hand webcam apps must assume that TRY_FMT will just map an unsupported pixel format to a valid pixel format since that is what uvc does. And a webcam app that doesn't support uvc can't be called a webcam app :-) Regards, Hans > Thanks > Guennadi > >>> If we have a spec, that says A, and some drivers drivers do A, but others >>> do B, and we want to change the specs to B? Instead of either changing the >>> (wrong) drivers to A (yes, some applications expect that wrong behaviour) >>> or at least extending the spec to allow both A and B? >> >> -- >> Regards, >> >> Laurent Pinchart > > --- > Guennadi Liakhovetski, Ph.D. > Freelance Open-Source Software Developer > http://www.open-technology.de/ > -- 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
