Hi Laurent,
On Mon, May 07, 2012 at 12:44:45PM +0200, Laurent Pinchart wrote:
> Hi Sakari,
>
> On Sunday 06 May 2012 21:14:02 Sakari Ailus wrote:
> > Laurent Pinchart wrote:
> > > On Saturday 05 May 2012 16:09:33 Sakari Ailus wrote:
> > ...
> >
> > >> The pixel format and the image size at the pad are clearly format
> > >> (VIDIOC_SUBDEV_S_FMT) but the other things are related to pads but not
> > >> format.
> > >>
> > >> I see them different kinds of properties of pads. That suggests we might
> > >> be better renaming the option (-f) to something else as well.
> > >
> > > You like breaking interfaces, don't you ? :-D
> >
> > I thought you said we have no stable release yet. :-D
> >
> > The selection interface on subdevs is currently used to change format
> > related things (cropping and scaling, for example) but it was one of
> > Sylwester's patches ("V4L: Add auto focus targets to the selections
> > API") that adds a focus window target to the V4L2 selection interface. I
> > don't see why it couldn't be present on subdevs, too. That's got nothing
> > to do with the image format.
> >
> > I've been pondering a bit using another option to configure things
> > related to selections. Conveniently "-s" is free. We could leave the
> > crop things to -f but remove the documentation related to them.
>
> It would then become much more complex to setup a complete pipeline in a
> single command line, unless we completely modify the way the command line is
> parsed.
>
> What would you think about renaming -f to -V (long option --video or --v4l2) ?
> media-ctl will hopefully be used for non-V4L2 devices in the future, so
> subsystem-specific options will likely be needed.
Sounds like a very good idea to me; it solves the issue properly and makes
the V4L2 functionality better separated in media-ctl. I'll put that on top
of the existing stack.
> > I'm fine with keeping the things as they are for now, too, but in that
> > case we should recognise that -f will not be for formats only. Or we
> > split handling selections into separate options, but I don't like that
> > idea either.
> >
> > >>> I find the '/' a bit confusing compared to the ' ' (but I think you find
> > >>> the space confusing compared to '/' :-)). I also wonder whether we
> > >>> shouldn't just drop 'fmt:', as there can be a single format only.
> > >>
> > >> You can set it multiple times, or you may not set it at all. That's why I
> > >> think we should explicitly say it's the format.
> > >
> > > Not at all makes sense, but why would you set it multiple times ?
> >
> > I guess that's not a very practical use case, albeit there may be
> > dependencies between the two: Guennadi had a piece of hardware where the
> > hardware cropping or scaling capabilities depended on the format.
>
> We don't have a way to handle that cleanly in the V4L2 API, do we ?
No, not really. The user has to set the format before any selection targets
on either of the pads, wchich is a little bit against the documentation. But
this is a very special case.
Regards,
--
Sakari Ailus
e-mail: sakari.ailus@xxxxxx jabber/XMPP/Gmail: sailus@xxxxxxxxxxxxxx
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