On Sun, 2011-06-12 at 15:23 +0200, Hans Verkuil wrote: > 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. I use /dev/radio & /dev/video24 for FM radio using ivtv-radio, myself. BTW, the cx18-alsa module annoys me as a developer. PulseAudio holds the device nodes open, pinning the cx18-alsa and cx18 modules in kernel. When killed, PulseAudio respawns rapidly and reopens the nodes. Unloading cx18 for development purposes is a real pain when the cx18-alsa module exists. > 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. Gah, I think you are right. It probably was a multiple open() problem on /dev/radio for the app author. I do remember researching that cx18 and ivtv are single open() on /dev/radio. I also remember finding that the V4L2 spec doesn't require multiple opens, and implies drivers need not support it in at least two places: "Multiple Opens In general, V4L2 devices can be opened more than once. When this is supported by the driver, ..." "Name v4l2-open â Open a V4L2 device ... EBUSY The driver does not support multiple opens and the device is already in use. ..." Regards, Andy -- 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
