[alsa-devel] USB audio2.0 status interrupt endpoint

[Puneet Sharma]

On Thu, Mar 3, 2016 at 6:37 PM, Clemens Ladisch <clemens at ladisch.de> wrote:

> Puneet Sharma wrote:
> > As per my understanding, when the above interrupt endpoint is transferred
> > to host in response to Interrupt IN request, the host should send me a
> GET
> > CUR volume class-specific request to further qualify the cause of
> interrupt.
> >
> > However, I am not getting any class-specific request from host in
> response
> > to the status interrupt transferred to host.
> >
> > My query is do i need to implement a mixer interface in the uac2 kernel
> > driver to get the request or i am doing something wrong in the process.
>
> You must not send a notification for a unit ID that does not exist, so
> you must implement the mixer interface.
>
I have used a feature unit descriptor in the gadget driver with volume
control.
The Feature unit is inserted between Input and output terminal having
a unique Unit ID.

>
> And you will get a request to read the control's current volume only if
> some application that cares about the value (e.g., alsamixer) actually
> happens to be running on the host.
>
> Yes, I understand your point now.
After running alsamixer on host, I am able to send volume request to device
as well get volume request from host in response to status interrupt.

>
> Regards,
> Clemens
>