Re: Hardware interface constant for Bluetooth

[Marcel Holtmann <marcel@holtmann.org>]

Hi Jaroslav,

> > this is a little bit tricky. Besides the native support for transporting
> > PCM data over a Bluetooth SCO channel, the headset/handsfree profile
> > uses a RFCOMM channel (serial port emulation) for additional settings.
> > On this channel they use AT commands and actually I don't wanna put a AT
> > parser into the kernel. It is in somekind possible, but I still think
> > that it does not belong there, because it is profile specific and a
> > Bluetooth profile is an application and applications should run in user
> > space. On the other hand you still need to create that SCO channel from
> > user space with somekind of ioctl, because the kernel can't know when
> > this channel must be established. It depends on some AT commands that
> > are send over the RFCOMM channel.
> > 
> > So my plan is to write a kernel module that is reponsible for the SCO
> > audio traffic. This registers as a soundcard with the ALSA subsystem and
> > it also registers a Bluetooth HWDEP. There is no initial PCM device
> > registered with this soundcard. These are only added when a SCO channel
> > is opened from the peer side or requested through an ioctl on the HWDEP
> > interface. Besides this the HWDEP would also control the mixer settings,
> > because these are exchanged over the RFCOMM channel.
> > 
> > Do you think this makes sense?
> 
> Yep, the management of PCM devices belongs into the hwdep API - except the
> mixer controls. You should map the possible mixer and other controls using
> the universal control API.
> 
> The SNDRV_HWDEP_IFACE_BLUETOOTH definition was added to the ALSA CVS tree.

I will look at the universal control API when the basics of the PCM
handling are done. Thanks.

Regards

Marcel




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