[alsa-devel] Unregister a card from userspace?

[Ricard Wanderlof]

On Wed, 11 Nov 2015, Felipe Ferreri Tonello wrote:

> >> How is your architecture? If you use one card for each probe of module
> >> then each bind should create one device, right?
> > 
> > In this case, it is a device which is located on the SoC. There is only 
> > one instance of it. When the module is loaded, it loads a codec driver 
> > with its associated DAI driver, a PCM driver, snd-soc-dummy-dai, and then 
> > a machine driver to tie it all together, finally registering the card with 
> > ALSA.
> > 
> > Looking in /sys/bus/platform/devices, there seems to be one device created 
> > for the codec itself, and one for the machine driver. I don't know if 
> > that's right or wrong, the ALSA driver hierarchy works in the sense that I 
> > can capture audio from it anyway.
> > 
> 
> What exactly do you want? If it is driver that register and unregister 
> cards based on the user interaction of probing and removing that module 
> from user-space, then you are not looking for a driver. What you are 
> looking for is just a kernel module. The only way of interacting with it 
> is dealing with module_init and module_exit.

What I was aiming for was that when I load this particular module, it 
ultimately calls snd_soc_register_card in its probe function, so that the 
device in question becomes available for ALSA once the module has been 
loaded. And then if I want to remove the driver I simply unload the module 
which allows it to go away.

The underlying reason for this rigmarole is rather complex, suffice to say 
at this stage that part of the hardware can be used for other mutually 
exclusive tasks.

> On the other hand, if in fact you want a driver, then check
> sound/drivers/dummy.c for an example. You can also read the
> Documentation/driver-model/platform.txt for more info.

Thanks for the pointers Filipe, I'll have a look there.

/Ricard
-- 
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
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