From mboxrd@z Thu Jan  1 00:00:00 1970
From: Clemens Ladisch <clemens@ladisch.de>
Subject: Re: Possible message repeat
Date: Wed, 13 Jun 2012 16:48:50 +0200
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To: Brent Weatherall <brentweatherall@gmail.com>
Cc: alsa-devel@alsa-project.org, Laurent Pinchart <laurent.pinchart@ideasonboard.com>
List-Id: alsa-devel@alsa-project.org

Brent Weatherall wrote:
> I am trying to specify an extension to the UAC specification and then
> write a user space driver/application to use the extension when
> a device that supports it is available in Linux.
>
> Can anyone assist me with the best path forward for writing user space code
> to use the XU I am going to define?  Meaning generically speaking how to
> use UAC XU controls in ALSA.

XU controls cannot be used generically.  The driver must be extended to
create the vendor-specific controls of this particular device; or the
driver could get a function to allow userspace to add such controls.

> it appears that any XU controls would be processed through usbmixer.c,
> but I don't see how to use the code in usbmixer from user space.

That code creates mixer controls.

> And so far I can't tell what source usbmixer resides in.

sound/usb/mixer.c in the kernel source, although such extensions
probably belong into mixer_quirks.c.


Regards,
Clemens