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. 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
