On Thu 21 June 2012 08:53:25 Sakari Ailus wrote:
> Hi Hans,
>
> On Wed, Jun 20, 2012 at 01:00:34PM +0200, Hans Verkuil wrote:
> > On Wed 20 June 2012 12:25:09 Sakari Ailus wrote:
> > > Hi Scott,
> > >
> > > Scott Jiang wrote:
> > > >>>>>> I would expect that the combination of v4l2_mbus_framefmt +
> > > >>>>>> v4l2_dv_timings
> > > >>>>>> gives you the information you need.
> > > >>>>>>
> > > >>>>> I can solve this problem in HD, but how about SD? Add a fake
> > > >>>>> dv_timings ops in SD decoder driver?
> > > >>>>>
> > > >>>>
> > > >>>> No, you add g/s_std instead. SD timings are set through that API. It
> > > >>>> is
> > > >>>> not so
> > > >>>> much that you give explicit timings, but that you give the SD
> > > >>>> standard.
> > > >>>> And from
> > > >>>> that you can derive the timings (i.e., one for 60 Hz formats, and
> > > >>>> one for
> > > >>>> 50 Hz
> > > >>>> formats).
> > > >>>>
> > > >>> Yes, it's a solution for decoder. I can convert one by one. But how
> > > >>> about sensors?They can output VGA, QVGA or any manual resolution.
> > > >>> My question is why we can't add these blanking details in
> > > >>> v4l2_mbus_framefmt? This structure is used to describe frame format on
> > > >>> media bus. And I believe blanking data also transfer on this bus. I
> > > >>> know most hardwares don't care about blanking areas, but some hardware
> > > >>> such as PPI does. PPI can capture ancillary data both in herizontal
> > > >>> and vertical interval. Even it works in active video only mode, it
> > > >>> expects to get total timing info.
> > > >>
> > > >>
> > > >> Since I don't know what you are trying to do, it is hard for me to give
> > > >> a good answer.
> > > >>
> > > >> So first I'd like to know if this is related to the adv7842 chip? I
> > > >> think
> > > >> you are talking about how this is done in general, and not
> > > >> specifically in
> > > >> relationship to the adv7842. At least, I can't see how/why you would
> > > >> hook up a sensor to the adv7842.
> > > > Yes, I want to have a general solution.
> > > >
> > > >>
> > > >> Sensor configuration is a separate topic, and something I am not an
> > > >> expert on. People like Sakari Ailus and Laurent Pinchart know much
> > > >> more about that than I do.
> > > >>
> > > >> I know that there is some support for blanking through low-level image
> > > >> source
> > > >> controls:
> > > >>
> > > >> http://hverkuil.home.xs4all.nl/spec/media.html#image-source-controls
> > > >>
> > > >> This is experimental and if this is insufficient for your requirements
> > > >> than
> > > >> I suggest posting a message where you explain what you need, CC-ing the
> > > >> people
> > > >> I mentioned,
> > > >>
> > > >> Most of these APIs are quite new and by marking them as experimental
> > > >> we can
> > > >> make changes later if it turns out it is not good enough.
> > > > I remember I have discussed this topic with Sakari before but without
> > > > working out a solution.
> > > > In conclusion, my current solution is:
> > > > if (HD)
> > > > dv_timings
> > > > else if (SD)
> > > > fill in according to PAL/NTSC timings
> > > > else
> > > > get control of V4L2_CID_HBLANK/V4L2_CID_VBLANK
> > > >
> > > > I guess this can solve my problem. But it's a bit complicated. If
> > > > v4l2_mbus_framefmt contains thes members, it's convenient and simple.
> > >
> > > Adding horizontal and vertical blanking as fields to struct
> > > v4l2_mbus_framefmt was discussed long ago --- I even sent a patch doing
> > > that AFAIR. It'd have been a simple solution, yes. The resulting
> > > discussion concluded, however, that as the horizontal or vertical
> > > blanking are not really a property of the image format, and generally
> > > only affect timing (frame rate, they do not belong to this struct.
> > >
> > > Also changing them while streaming is almost always possible (except in
> > > your case, I believe) whereas the rest of the fields are considered
> > > static. It'd be difficult for the user to know which fields can be
> > > actually changed while streamon, and which can't.
> > >
> > > For these reasons (AFAIR) we chose to use controls instead.
> > >
> > > I think the right solution to the problem when it comes to sensors, is
> > > to mark these controls busy from the bridge driver if the bridge
> > > hardware can't cope with changes in blanking. The control framework
> > > doesn't support this currently but it might not be that much of work to
> > > implement it. Such feature would definitely have to be used with care.
> > >
> > > Hans, what do you think?
> >
> > That's already supported for a long time. If the control flag
> > V4L2_CTRL_FLAG_GRABBED
> > is set, then the control is marked busy.
> >
> > There aren't many drivers that use this flag, but some do.
>
> The problem is it's a flag. In this case the driver marking the control busy
> would be a different driver from the one that implements it, and I don't
> think we could trust only one of the drivers will want to modify it. So it'd
> have to be a counter instead.
Why would another driver than the bridge driver want to change this?
Right now it is no problem for the bridge driver to change the grabbed flag of
a control of a subdev driver.
If this would have to be implemented as a counter, then that would make things
more complicated. But I'd like to see an actual need for that before I would
consider implementing this.
> That could still require special handling in some cases so we could specify
> which controls may be grabbed by other drivers and when as the drivers may
> want to modify the controls themselves, too.
Well, if someone grabbed the control, then no driver or application should be
able to modify it until it is 'ungrabbed'.
Regards,
Hans
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