On Mon August 13 2012 15:13:34 Hans de Goede wrote:
Hi,
<snip>
How to handle tuner ownership if both a video and radio node share the same tuner?
Obvious rules:
- Calling S_FREQ, S_TUNER, S_MODULATOR or S_HW_FREQ_SEEK will change owner or return EBUSY if streaming is in progress.
That won't work, as there is no such thing as streaming from a radio node,
There is, actually: read() for RDS data and alsa streaming (although that might be hard to detect in the case of USB audio).
I suggest we go with the simple approach we discussed at our last meeting in your Dutch House: Calling S_FREQ, S_TUNER, S_MODULATOR or S_HW_FREQ_SEEK will make an app the tuner-owner, and *closing* the device handle makes an app release its tuner ownership. If an other app already is the tuner owner -EBUSY is returned.
So the ownership is associated with a filehandle?
- Ditto for STREAMON, read/write and polling for read/write.No, streaming and tuning are 2 different things, if an app does both, it will likely tune before streaming, but in some cases a user may use a streaming only app together with say v4l2-ctl to do the actual tuning. I think keeping things simple here is key. Lets just treat the "tuner" and "stream" as 2 separate entities with a separate ownership.
That would work provided the ownership is associated with a filehandle.
- Ditto for ioctls that expect a valid tuner configuration like QUERYSTD.QUERY is a read only ioctl, so it should not be influenced by any ownership, nor imply ownership.
It is definitely influenced by ownership, since if the tuner is in radio mode, then it can't detect a standard. Neither is this necessarily a passive call as some (mostly older) drivers need to switch the receiver to different modes in order to try and detect the current standard.
- Just opening a device node should *not* switch ownership.Ack!
But it is not clear what to do when any of these ioctls are called: - G_FREQUENCY: could just return the last set frequency for radio or TV: requires that that is remembered when switching ownership. This is what happens today, so G_FREQUENCY does not have to switch ownership.Ack.
- G_TUNER: the rxsubchans, signal and afc fields all require ownership of the tuner. So in principle you would want to switch ownership when G_TUNER is called. On the other hand, that would mean that calling v4l2-ctl --all -d /dev/radio0 would change tuner ownership to radio for /dev/video0. That's rather unexpected. It is possible to just set rxsubchans, signal and afc to 0 if the device node doesn't own the tuner. I'm inclined to do that.Right, G_TUNER should not change ownership, if the tuner is currently in radio mode and a G_TUNER is done on the video node just 0 out the fields which we cannot fill with useful info.
- Should closing a device node switch ownership? E.g. if nobody has a radio device open, should the tuner switch back to TV mode automatically? I don't think it should.+1 on delaying the mode switch until it is actually necessary to switch mode.
- How about hybrid tuners?No opinion.
Regards,
Hans