插着USB mic开机时，系统没有声音问题

Platform: Rockchip
OS: Android 7.1.2
Kernel: 4.4

1.问题描述：当插上USB mic录音设备开机时，系统没有声音。开机后再接上USB mic，此时声音就正常。

2.问题分析：

接着usb mic开机时，MT100:/ # cat /proc/asound/cards
cat /proc/asound/cards
0 [Device ]: USB-Audio - USB Audio Device
USB Audio Device at usb-ff540000.usb-1.1, full speed
1 [rockchipes8323c]: rockchip_es8323 - rockchip,es8323-codec
rockchip,es8323-codec
开机后再接usb mic时，MT100:/ # cat /proc/asound/cards
cat /proc/asound/cards
0 [rockchipes8323c]: rockchip_es8323 - rockchip,es8323-codec
rockchip,es8323-codec
1 [Device ]: USB-Audio - USB Audio Device
USB Audio Device at usb-ff540000.usb-1.1, full speed

可见，这种情况是由于USB声卡被优先挂载，导致系统声卡不出声音。

3.解决方案：将usb声卡注册顺序延后

diff --git a/sound/usb/card.c b/sound/usb/card.c
old mode 100644
new mode 100755
index 83336bb..f3323ed
--- a/sound/usb/card.c
+++ b/sound/usb/card.c
@@ -83,6 +83,11 @@ static int device_setup[SNDRV_CARDS]; /* device parameter for this card */
 static bool ignore_ctl_error;
 static bool autoclock = true;
 
+#define CONFIG_SND_RK_SOC
+#ifdef CONFIG_SND_RK_SOC
+#define USB_AUDIO_CARD_NUM     3
+#endif
+
 module_param_array(index, int, NULL, 0444);
 MODULE_PARM_DESC(index, "Index value for the USB audio adapter.");
 module_param_array(id, charp, NULL, 0444);
@@ -369,9 +374,14 @@ static int snd_usb_audio_create(struct usb_interface *intf,
                dev_err(&dev->dev, "unknown device speed %d
", snd_usb_get_speed(dev));
                return -ENXIO;
        }
-
-       err = snd_card_new(&intf->dev, index[idx], id[idx], THIS_MODULE,
+       
+       #ifdef CONFIG_SND_RK_SOC
+       err = snd_card_new(&intf->dev, USB_AUDIO_CARD_NUM, id[idx], THIS_MODULE,
+                          0, &card);
+       #else
+               err = snd_card_new(&intf->dev, index[idx], id[idx], THIS_MODULE,
                           0, &card);
+       #endif     
        if (err < 0) {
                dev_err(&dev->dev, "cannot create card instance %d
", idx);
                return err;

加上以上修改，即可解决此问题。

 usb声卡注册的设备号固定注册为3，不占用系统默认的0即可。