Android4.0 声卡配置-高通msm8916移植

一个正常的UAC设备插入Android 7.0是默认打开UAC配置的，打印的log如下：

[ 2367.490491] usb -3.2: new full-speed USB device number  using xhci_hcd
[ 2367.580010] usb -3.2: New USB device found, idVendor=0d8c, idProduct=
[ 2367.580018] usb -3.2: New USB device strings: Mfr=, Product=, SerialNumber=
[ 2367.580023] usb -3.2: Product: USB PnP Audio Device
[ 2367.580027] usb -3.2: Manufacturer: C-Media Electronics Inc.
[ 2367.581679] input: C-Media Electronics Inc. USB PnP Audio Device as /devices/pci0000:/::14.0/usb3/-/-3.2/-3.2:1.2/:0D8C:0132.0004/input/input18
[ 2367.581999] hid-generic :0D8C:0132.0004: input,hidraw3: USB HID v1. Device [C-Media Electronics Inc. USB PnP Audio Device] on usb-::14.0-3.2/input2
[ 2367.913280] usbcore: registered new interface driver snd-usb-audio

而Android4.0是没有默认打开，是需要进行相应的配置的；这里可以看到其驱动程序为snd-usb-audio，依据这个关键词在内核中查找到如下内容：

 root@ubuntu:/home/lh/work/git/ML16/kernel# grep "registered new interface driver" ./ -rn
 ./drivers/usb/core/driver.c::        pr_info("%s: registered new interface driver %s\n",

需要在 /kernel/arch/arm/configs目录下增加msm8916_defconfig和msm8916-perf_defconfig配置;

在AndroidBoard.mk就已经定义了我们kernel配置文件的属性：

CONFIG_SND_USB_AUDIO=y就行了，因为sound/usb/中的makefile包含了:

在sound/usb/card.c

 static struct usb_driver usb_audio_driver = {
     .name =     "snd-usb-audio",
     .probe =    usb_audio_probe,
     .disconnect =   usb_audio_disconnect,
     .suspend =  usb_audio_suspend,
     .resume =   usb_audio_resume,
     .id_table = usb_audio_ids,
     .supports_autosuspend = ,
 };

根据probe方法snd_usb_audio_probe调用了snd_usb_apply_boot_quirk和snd_card_register，查到了：

 static int usb_audio_probe(struct usb_interface *intf,
                const struct usb_device_id *id)
 {
     struct snd_usb_audio *chip;
     chip = snd_usb_audio_probe(interface_to_usbdev(intf), intf, id);
     if (chip) {
         usb_set_intfdata(intf, chip);
         return ;
     } else
         return -EIO;
 }

 // linux-3.4.y/sound/usb/quirks.c
 int snd_usb_apply_boot_quirk(struct usb_device *dev,
                  struct usb_interface *intf,
                  const struct snd_usb_audio_quirk *quirk)
 {
     u32 id = USB_ID(le16_to_cpu(dev->descriptor.idVendor),
             le16_to_cpu(dev->descriptor.idProduct));

     switch (id) {
     case USB_ID(0x041e, 0x3000):
         /* SB Extigy needs special boot-up sequence */
         /* if more models come, this will go to the quirk list. */
         return snd_usb_extigy_boot_quirk(dev, intf);

     case USB_ID(0x041e, 0x3020):
         /* SB Audigy 2 NX needs its own boot-up magic, too */
         return snd_usb_audigy2nx_boot_quirk(dev);

     case USB_ID(0x10f5, 0x0200):
         /* C-Media CM106 / Turtle Beach Audio Advantage Roadie */
         return snd_usb_cm106_boot_quirk(dev);

     case USB_ID(0x0d8c, 0x0102):
         /* C-Media CM6206 / CM106-Like Sound Device */
     case USB_ID(0x0ccd, 0x00b1): /* Terratec Aureon 7.1 USB */
         return snd_usb_cm6206_boot_quirk(dev);

     case USB_ID(0x133e, 0x0815):
         /* Access Music VirusTI Desktop */
         return snd_usb_accessmusic_boot_quirk(dev);

     case USB_ID(0x17cc, 0x1000): /* Komplete Audio 6 */
     case USB_ID(0x17cc, 0x1010): /* Traktor Audio 6 */
     case USB_ID(0x17cc, 0x1020): /* Traktor Audio 10 */
         return snd_usb_nativeinstruments_boot_quirk(dev);
     case USB_ID(0x0763, 0x2012):  /* M-Audio Fast Track Pro USB */
         return snd_usb_fasttrackpro_boot_quirk(dev);
     }

     return ;
 }

snd_usb_audio_probe：

 /*
  * probe the active usb device
  *
  * note that this can be called multiple times per a device, when it
  * includes multiple audio control interfaces.
  *
  * thus we check the usb device pointer and creates the card instance
  * only at the first time.  the successive calls of this function will
  * append the pcm interface to the corresponding card.
  */
 static struct snd_usb_audio *
 snd_usb_audio_probe(struct usb_device *dev,
             struct usb_interface *intf,
             const struct usb_device_id *usb_id)
 {
     const struct snd_usb_audio_quirk *quirk = (const struct snd_usb_audio_quirk *)usb_id->driver_info;
     int i, err;
     struct snd_usb_audio *chip;
     struct usb_host_interface *alts;
     int ifnum;
     u32 id;

     alts = &intf->altsetting[];
     ifnum = get_iface_desc(alts)->bInterfaceNumber;
     id = USB_ID(le16_to_cpu(dev->descriptor.idVendor),
             le16_to_cpu(dev->descriptor.idProduct));
     if (quirk && quirk->ifnum >=  && ifnum != quirk->ifnum)
         goto __err_val;

     if (snd_usb_apply_boot_quirk(dev, intf, quirk) < )
         goto __err_val;

     /*
      * found a config.  now register to ALSA
      */

     /* check whether it's already registered */
     chip = NULL;
     mutex_lock(&register_mutex);
     for (i = ; i < SNDRV_CARDS; i++) {
         if (usb_chip[i] && usb_chip[i]->dev == dev) {
             if (usb_chip[i]->shutdown) {
                 snd_printk(KERN_ERR "USB device is in the shutdown state, cannot create a card instance\n");
                 goto __error;
             }
             chip = usb_chip[i];
             chip->probing = ;
             break;
         }
     }
     if (! chip) {
         /* it's a fresh one.
          * now look for an empty slot and create a new card instance
          */
         for (i = ; i < SNDRV_CARDS; i++)
             if (enable[i] && ! usb_chip[i] &&
                 (vid[i] == - || vid[i] == USB_ID_VENDOR(id)) &&
                 (pid[i] == - || pid[i] == USB_ID_PRODUCT(id))) {
                 if (snd_usb_audio_create(dev, i, quirk, &chip) < ) {
                     goto __error;
                 }
                 snd_card_set_dev(chip->card, &intf->dev);
                 chip->pm_intf = intf;
                 break;
             }
         if (!chip) {
             printk(KERN_ERR "no available usb audio device\n");
             goto __error;
         }
     }

     /*
      * For devices with more than one control interface, we assume the
      * first contains the audio controls. We might need a more specific
      * check here in the future.
      */
     if (!chip->ctrl_intf)
         chip->ctrl_intf = alts;

     chip->txfr_quirk = ;
     err = ; /* continue */
     if (quirk && quirk->ifnum != QUIRK_NO_INTERFACE) {
         /* need some special handlings */
         if ((err = snd_usb_create_quirk(chip, intf, &usb_audio_driver, quirk)) < )
             goto __error;
     }

     if (err > ) {
         /* create normal USB audio interfaces */
         if (snd_usb_create_streams(chip, ifnum) <  ||
             snd_usb_create_mixer(chip, ifnum, ignore_ctl_error) < ) {
             goto __error;
         }
     }

     /* we are allowed to call snd_card_register() many times */
     if (snd_card_register(chip->card) < ) {
         goto __error;
     }

     usb_chip[chip->index] = chip;
     chip->num_interfaces++;
     chip->probing = ;
     mutex_unlock(&register_mutex);
     return chip;

  __error:
     if (chip) {
         if (!chip->num_interfaces)
             snd_card_free(chip->card);
         chip->probing = ;
     }
     mutex_unlock(&register_mutex);
  __err_val:
     return NULL;
 }

probe依次调用了：

 snd_usb_apply_boot_quirk
 snd_usb_audio_create
 snd_usb_create_quirk
 snd_usb_create_streams
  snd_usb_create_stream
   snd_usb_parse_audio_interface 这里根据usb的信息解析成pcm参数（如声道数量，采样率等等）

 snd_usb_create_mixer
 snd_card_register

总结：

UAC设备的参数是通过USB描述符确定的。比如声道是bNrChannels，位深是bBitResolution，采样率是bSamFreqType。截取其中一段说明：

bNrChannels
bSubframeSize
bBitResolution
bSamFreqType             Discrete
tSamFreq[ ]
tSamFreq[ ]
tSamFreq[ ]
tSamFreq[ ]
tSamFreq[ ]
tSamFreq[ ]
tSamFreq[ ]        

声道1，位深16，波特率8000~48000。