Re: [Q] Why is it needed to add an alsa module to v4l audio capture devices?

[Mauro Carvalho Chehab <mchehab@redhat.com>]

Em 07-06-2012 15:26, Ezequiel Garcia escreveu:
> Hi all,
> 
> (I hope this is a genuine question, and I'm not avoiding my own homework here.)
> 
> I'm trying to support the audio part of the stk1160 usb bridge
> (similar to em28xx).
> Currently, the snd-usb-audio module is being loaded when I physically
> plug my device,
> but I can't seem to capture any sound with vlc.

Laurent already explained why snd-usb-audio is loaded.
> 
> I still have to research and work a lot to understand the connection
> between my device
> and alsa, and altough I could write a working module similar to
> em28xx-alsa.ko, I still
> can't figure out why do I need to write one in the first place.

On em28xx, some devices use UAC (USB Audio Class), while others use a proprietary
vendor class protocol. The em28xx-alsa module is used only for the devices with a
vendor class.
> 
> Why is this module suffficient for gspca microphone devices (gspca, to name one)
> and why is a new alsa driver needed for em28xx (or stk1160)?

On em28xx, even the ones that use UAC require some configuration, for audio to work.

some setup is required to configure the audio input associated with a video input,
and to enable clock for the audio sampler. Such setup is made when a video input is
selected. You likely need something similar for stk1160.

Regards,
Mauro