ALSA: snd-usb: implement new endpoint streaming model

This patch adds a new generic streaming logic for audio over USB.

It defines a model (snd_usb_endpoint) that handles everything that
is related to an USB endpoint and its streaming. There are functions to
activate and deactivate an endpoint (which call usb_set_interface()),
and to start and stop its URBs. It also has function pointers to be
called when data was received or is about to be sent, and pointer to
a sync slave (another snd_usb_endpoint) that is informed when data has
been received.

A snd_usb_endpoint knows about its state and implements a refcounting,
so only the first user will actually start the URBs and only the last
one to stop it will tear them down again.

With this sort of abstraction, the actual streaming is decoupled from
the pcm handling, which makes the "implicit feedback" mechanisms easy to
implement.

In order to split changes properly, this patch only adds the new
implementation but leaves the old one around, so the the driver doesn't
change its behaviour. The switch to actually use the new code is
submitted separately.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 1 insertions, 0 deletions

diff --git a/sound/usb/usbaudio.h b/sound/usb/usbaudio.h
index a16c21d2d7ed..b8233ebe250f 100644
--- a/sound/usb/usbaudio.h
+++ b/sound/usb/usbaudio.h
@@ -47,6 +47,7 @@ struct snd_usb_audio {
         int num_suspended_intf;
 
         struct list_head pcm_list;      /* list of pcm streams */
+        struct list_head ep_list;       /* list of audio-related endpoints */
         int pcm_devs;
 
         struct list_head midi_list;     /* list of midi interfaces */