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* u_audio.h -- interface to USB gadget "ALSA sound card" utilities
* Copyright (C) 2016
* Author: Ruslan Bilovol <>
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* GNU General Public License for more details.
#ifndef __U_AUDIO_H
#define __U_AUDIO_H
#include <linux/usb/composite.h>
struct uac_params {
/* playback */
int p_chmask; /* channel mask */
int p_srate; /* rate in Hz */
int p_ssize; /* sample size */
/* capture */
int c_chmask; /* channel mask */
int c_srate; /* rate in Hz */
int c_ssize; /* sample size */
int req_number; /* number of preallocated requests */
struct g_audio {
struct usb_function func;
struct usb_gadget *gadget;
struct usb_ep *in_ep;
struct usb_ep *out_ep;
/* Max packet size for all in_ep possible speeds */
unsigned int in_ep_maxpsize;
/* Max packet size for all out_ep possible speeds */
unsigned int out_ep_maxpsize;
/* The ALSA Sound Card it represents on the USB-Client side */
struct snd_uac_chip *uac;
struct uac_params params;
static inline struct g_audio *func_to_g_audio(struct usb_function *f)
return container_of(f, struct g_audio, func);
static inline uint num_channels(uint chanmask)
uint num = 0;
while (chanmask) {
num += (chanmask & 1);
chanmask >>= 1;
return num;
* g_audio_setup - initialize one virtual ALSA sound card
* @g_audio: struct with filled params, in_ep_maxpsize, out_ep_maxpsize
* @pcm_name: the id string for a PCM instance of this sound card
* @card_name: name of this soundcard
* This sets up the single virtual ALSA sound card that may be exported by a
* gadget driver using this framework.
* Context: may sleep
* Returns zero on success, or a negative error on failure.
int g_audio_setup(struct g_audio *g_audio, const char *pcm_name,
const char *card_name);
void g_audio_cleanup(struct g_audio *g_audio);
int u_audio_start_capture(struct g_audio *g_audio);
void u_audio_stop_capture(struct g_audio *g_audio);
int u_audio_start_playback(struct g_audio *g_audio);
void u_audio_stop_playback(struct g_audio *g_audio);
#endif /* __U_AUDIO_H */