On Sunday, June 12, 2011 14:53:06 Andy Walls wrote:
> On Sun, 2011-06-12 at 14:30 +0200, Hans Verkuil wrote:
> > On Sunday, June 12, 2011 14:13:30 Mauro Carvalho Chehab wrote:
> > > Em 12-06-2011 08:59, Mauro Carvalho Chehab escreveu:
> > > > Em 12-06-2011 08:36, Hans Verkuil escreveu:
> > > >>>> What about this:
> > > >>>>
> > > >>>> Opening /dev/radio effectively starts the radio mode. So if there is
> > > >>>> TV
> > > >>>> capture in progress, then the open should return -EBUSY. Otherwise it
> > > >>>> switches the tuner to radio mode. And it stays in radio mode until
> > > >>>> the
> > > >>>> last filehandle of /dev/radio is closed. At that point it will
> > > >>>> automatically
> > > >>>> switch back to TV mode (if there is one, of course).
> > > >>>
> > > >>> No. This would break existing applications. The mode switch should be
> > > >>> done
> > > >>> at S_FREQUENCY (e. g. when the radio application is tuning into a
> > > >>> channel).
> > > >>
> > > >> This is not what happens today as the switch to radio occurs as soon
> > > >> as you open
> > > >> the radio node. It's the reason for the s_radio op.
> > > >
> > > > The s_radio op is something that I wanted to remove. It was there in
> > > > the past to feed
> > > > the TV/radio hint logic. I wrote a patch for it, but I ended by
> > > > discarding from my
> > > > final queue (I can't remember why).
> > > >
> > > > I think that the hint logic were completely removed, but we may need to
> > > > take a look
> > > > on the callers for s_radio. I'll check it right now.
> > > >
> > >
> > > The s_radio callback requires some care, as it is used on several places.
> > > It is probably
> > > safe to remove it from tuner, but a few sub-drivers like msp3400 needs
> > > it. The actual
> > > troubles seem to happen at the bridge drivers that call it during open().
> > > It should be
> > > called only at s_frequency. I opted to keep the callback just to avoid
> > > having a bridge
> > > driver switching its registers to radio mode, and not having the tuner
> > > following it.
> > >
> > > If we move the radio mode switch at the bridge drivers to s_frequency
> > > only, we can just
> > > remove this callback from tuner, letting it to be implemented only at the
> > > audio decoders.
> >
> > Why would the audio decoders need it? If we do the mode switch when s_freq
> > is
> > called, then the audio decoders can do the same and s_radio can disappear
> > completely.
> >
> > I would like that, but I'm a bit afraid of application breakage since we're
> > changing
> > the behavior of /dev/radio. It seems that pretty much every video driver
> > with radio
> > capability is calling s_radio during open(): bttv, ivtv, saa7134,
> > usbvision, em28xx,
> > cx18, cx88, cx231xx and tm6000.
>
> I think ivtvhopper relies on it:
>
> http://www.gateways-home.org/wb/pages/mycoding/--ivtvhopper-java.php
>
> Also, per my recommendation, ivtvhopper changes radio freq by
> using /dev/video24, since V4L2 priorities got in the way:
>
> http://ivtvdriver.org/pipermail/ivtv-users/2010-December/010097.html
Well, radio support for ivtv is weird and we really need a ivtv-alsa (easier
said than done). Because it is so non-standard, I am not terribly concerned
about it.
BTW, one problem with /dev/radio and ivtv (and I think cx18 might have the same
problem) is that /dev/radio can be opened only once. A second attempt to open
it will result in -EBUSY. That's a driver bug. I wonder if that's really the
problem described in the link above instead of priority handling.
Regards,
Hans
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