usb-audio: support more than two channels of audio

This commit adds support for 5.1 and 7.1 audio playback.  This commit
adds a new property to usb-audio:

* multi=on|off
  Whether to enable the 5.1 and 7.1 audio support.  When off (default)
  it continues to emulate the old stereo-only device.  When on, it
  emulates a slightly different audio device that supports 5.1 and 7.1
  audio.

Signed-off-by: Kővágó, Zoltán <DirtY.iCE.hu@gmail.com>
Message-id: 98e96606228afa907fa238eac26573d5af63434a.1570996490.git.DirtY.iCE.hu@gmail.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

1 files changed, 366 insertions, 53 deletions

diff --git a/hw/usb/dev-audio.c b/hw/usb/dev-audio.c
index 74c99b1..e42bdfb 100644
--- a/hw/usb/dev-audio.c
+++ b/hw/usb/dev-audio.c
@@ -37,11 +37,15 @@
 #include "desc.h"
 #include "audio/audio.h"
 
+static void usb_audio_reinit(USBDevice *dev, unsigned channels);
+
 #define USBAUDIO_VENDOR_NUM     0x46f4 /* CRC16() of "QEMU" */
 #define USBAUDIO_PRODUCT_NUM    0x0002
 
 #define DEV_CONFIG_VALUE        1 /* The one and only */
 
+#define USBAUDIO_MAX_CHANNELS(s) (s->multi ? 8 : 2)
+
 /* Descriptor subtypes for AC interfaces */
 #define DST_AC_HEADER           1
 #define DST_AC_INPUT_TERMINAL   2
@@ -80,6 +84,27 @@ static const USBDescStrings usb_audio_stringtable = {
     [STRING_REAL_STREAM]        = "Audio Output - 48 kHz Stereo",
 };
 
+/*
+ * A USB audio device supports an arbitrary number of alternate
+ * interface settings for each interface.  Each corresponds to a block
+ * diagram of parameterized blocks.  This can thus refer to things like
+ * number of channels, data rates, or in fact completely different
+ * block diagrams.  Alternative setting 0 is always the null block diagram,
+ * which is used by a disabled device.
+ */
+enum usb_audio_altset {
+    ALTSET_OFF    = 0x00,         /* No endpoint */
+    ALTSET_STEREO = 0x01,         /* Single endpoint */
+    ALTSET_51     = 0x02,
+    ALTSET_71     = 0x03,
+};
+
+static unsigned altset_channels[] = {
+    [ALTSET_STEREO] = 2,
+    [ALTSET_51]     = 6,
+    [ALTSET_71]     = 8,
+};
+
 #define U16(x) ((x) & 0xff), (((x) >> 8) & 0xff)
 #define U24(x) U16(x), (((x) >> 16) & 0xff)
 #define U32(x) U24(x), (((x) >> 24) & 0xff)
@@ -87,7 +112,8 @@ static const USBDescStrings usb_audio_stringtable = {
 /*
  * A Basic Audio Device uses these specific values
  */
-#define USBAUDIO_PACKET_SIZE     192
+#define USBAUDIO_PACKET_SIZE_BASE 96
+#define USBAUDIO_PACKET_SIZE(channels) (USBAUDIO_PACKET_SIZE_BASE * channels)
 #define USBAUDIO_SAMPLE_RATE     48000
 #define USBAUDIO_PACKET_INTERVAL 1
 
@@ -121,7 +147,7 @@ static const USBDescIface desc_iface[] = {
                     0x01,                       /*  u8  bTerminalID */
                     U16(0x0101),                /* u16  wTerminalType */
                     0x00,                       /*  u8  bAssocTerminal */
-                    0x02,                       /* u16  bNrChannels */
+                    0x02,                       /*  u8  bNrChannels */
                     U16(0x0003),                /* u16  wChannelConfig */
                     0x00,                       /*  u8  iChannelNames */
                     STRING_INPUT_TERMINAL,      /*  u8  iTerminal */
@@ -156,14 +182,14 @@ static const USBDescIface desc_iface[] = {
         },
     },{
         .bInterfaceNumber              = 1,
-        .bAlternateSetting             = 0,
+        .bAlternateSetting             = ALTSET_OFF,
         .bNumEndpoints                 = 0,
         .bInterfaceClass               = USB_CLASS_AUDIO,
         .bInterfaceSubClass            = USB_SUBCLASS_AUDIO_STREAMING,
         .iInterface                    = STRING_NULL_STREAM,
     },{
         .bInterfaceNumber              = 1,
-        .bAlternateSetting             = 1,
+        .bAlternateSetting             = ALTSET_STEREO,
         .bNumEndpoints                 = 1,
         .bInterfaceClass               = USB_CLASS_AUDIO,
         .bInterfaceSubClass            = USB_SUBCLASS_AUDIO_STREAMING,
@@ -199,7 +225,7 @@ static const USBDescIface desc_iface[] = {
             {
                 .bEndpointAddress      = USB_DIR_OUT | 0x01,
                 .bmAttributes          = 0x0d,
-                .wMaxPacketSize        = USBAUDIO_PACKET_SIZE,
+                .wMaxPacketSize        = USBAUDIO_PACKET_SIZE(2),
                 .bInterval             = 1,
                 .is_audio              = 1,
                 /* Stereo Headphone Class-specific
@@ -247,17 +273,274 @@ static const USBDesc desc_audio = {
     .str  = usb_audio_stringtable,
 };
 
-/*
- * A USB audio device supports an arbitrary number of alternate
- * interface settings for each interface.  Each corresponds to a block
- * diagram of parameterized blocks.  This can thus refer to things like
- * number of channels, data rates, or in fact completely different
- * block diagrams.  Alternative setting 0 is always the null block diagram,
- * which is used by a disabled device.
- */
-enum usb_audio_altset {
-    ALTSET_OFF  = 0x00,         /* No endpoint */
-    ALTSET_ON   = 0x01,         /* Single endpoint */
+/* multi channel compatible desc */
+
+static const USBDescIface desc_iface_multi[] = {
+    {
+        .bInterfaceNumber              = 0,
+        .bNumEndpoints                 = 0,
+        .bInterfaceClass               = USB_CLASS_AUDIO,
+        .bInterfaceSubClass            = USB_SUBCLASS_AUDIO_CONTROL,
+        .bInterfaceProtocol            = 0x04,
+        .iInterface                    = STRING_USBAUDIO_CONTROL,
+        .ndesc                         = 4,
+        .descs = (USBDescOther[]) {
+            {
+                /* Headphone Class-Specific AC Interface Header Descriptor */
+                .data = (uint8_t[]) {
+                    0x09,                       /*  u8  bLength */
+                    USB_DT_CS_INTERFACE,        /*  u8  bDescriptorType */
+                    DST_AC_HEADER,              /*  u8  bDescriptorSubtype */
+                    U16(0x0100),                /* u16  bcdADC */
+                    U16(0x38),                  /* u16  wTotalLength */
+                    0x01,                       /*  u8  bInCollection */
+                    0x01,                       /*  u8  baInterfaceNr */
+                }
+            },{
+                /* Generic Stereo Input Terminal ID1 Descriptor */
+                .data = (uint8_t[]) {
+                    0x0c,                       /*  u8  bLength */
+                    USB_DT_CS_INTERFACE,        /*  u8  bDescriptorType */
+                    DST_AC_INPUT_TERMINAL,      /*  u8  bDescriptorSubtype */
+                    0x01,                       /*  u8  bTerminalID */
+                    U16(0x0101),                /* u16  wTerminalType */
+                    0x00,                       /*  u8  bAssocTerminal */
+                    0x08,                       /*  u8  bNrChannels */
+                    U16(0x063f),                /* u16  wChannelConfig */
+                    0x00,                       /*  u8  iChannelNames */
+                    STRING_INPUT_TERMINAL,      /*  u8  iTerminal */
+                }
+            },{
+                /* Generic Stereo Feature Unit ID2 Descriptor */
+                .data = (uint8_t[]) {
+                    0x19,                       /*  u8  bLength */
+                    USB_DT_CS_INTERFACE,        /*  u8  bDescriptorType */
+                    DST_AC_FEATURE_UNIT,        /*  u8  bDescriptorSubtype */
+                    0x02,                       /*  u8  bUnitID */
+                    0x01,                       /*  u8  bSourceID */
+                    0x02,                       /*  u8  bControlSize */
+                    U16(0x0001),                /* u16  bmaControls(0) */
+                    U16(0x0002),                /* u16  bmaControls(1) */
+                    U16(0x0002),                /* u16  bmaControls(2) */
+                    U16(0x0002),                /* u16  bmaControls(3) */
+                    U16(0x0002),                /* u16  bmaControls(4) */
+                    U16(0x0002),                /* u16  bmaControls(5) */
+                    U16(0x0002),                /* u16  bmaControls(6) */
+                    U16(0x0002),                /* u16  bmaControls(7) */
+                    U16(0x0002),                /* u16  bmaControls(8) */
+                    STRING_FEATURE_UNIT,        /*  u8  iFeature */
+                }
+            },{
+                /* Headphone Ouptut Terminal ID3 Descriptor */
+                .data = (uint8_t[]) {
+                    0x09,                       /*  u8  bLength */
+                    USB_DT_CS_INTERFACE,        /*  u8  bDescriptorType */
+                    DST_AC_OUTPUT_TERMINAL,     /*  u8  bDescriptorSubtype */
+                    0x03,                       /*  u8  bUnitID */
+                    U16(0x0301),                /* u16  wTerminalType (SPK) */
+                    0x00,                       /*  u8  bAssocTerminal */
+                    0x02,                       /*  u8  bSourceID */
+                    STRING_OUTPUT_TERMINAL,     /*  u8  iTerminal */
+                }
+            }
+        },
+    },{
+        .bInterfaceNumber              = 1,
+        .bAlternateSetting             = ALTSET_OFF,
+        .bNumEndpoints                 = 0,
+        .bInterfaceClass               = USB_CLASS_AUDIO,
+        .bInterfaceSubClass            = USB_SUBCLASS_AUDIO_STREAMING,
+        .iInterface                    = STRING_NULL_STREAM,
+    },{
+        .bInterfaceNumber              = 1,
+        .bAlternateSetting             = ALTSET_STEREO,
+        .bNumEndpoints                 = 1,
+        .bInterfaceClass               = USB_CLASS_AUDIO,
+        .bInterfaceSubClass            = USB_SUBCLASS_AUDIO_STREAMING,
+        .iInterface                    = STRING_REAL_STREAM,
+        .ndesc                         = 2,
+        .descs = (USBDescOther[]) {
+            {
+                /* Headphone Class-specific AS General Interface Descriptor */
+                .data = (uint8_t[]) {
+                    0x07,                       /*  u8  bLength */
+                    USB_DT_CS_INTERFACE,        /*  u8  bDescriptorType */
+                    DST_AS_GENERAL,             /*  u8  bDescriptorSubtype */
+                    0x01,                       /*  u8  bTerminalLink */
+                    0x00,                       /*  u8  bDelay */
+                    0x01, 0x00,                 /* u16  wFormatTag */
+                }
+            },{
+                /* Headphone Type I Format Type Descriptor */
+                .data = (uint8_t[]) {
+                    0x0b,                       /*  u8  bLength */
+                    USB_DT_CS_INTERFACE,        /*  u8  bDescriptorType */
+                    DST_AS_FORMAT_TYPE,         /*  u8  bDescriptorSubtype */
+                    0x01,                       /*  u8  bFormatType */
+                    0x02,                       /*  u8  bNrChannels */
+                    0x02,                       /*  u8  bSubFrameSize */
+                    0x10,                       /*  u8  bBitResolution */
+                    0x01,                       /*  u8  bSamFreqType */
+                    U24(USBAUDIO_SAMPLE_RATE),  /* u24  tSamFreq */
+                }
+            }
+        },
+        .eps = (USBDescEndpoint[]) {
+            {
+                .bEndpointAddress      = USB_DIR_OUT | 0x01,
+                .bmAttributes          = 0x0d,
+                .wMaxPacketSize        = USBAUDIO_PACKET_SIZE(2),
+                .bInterval             = 1,
+                .is_audio              = 1,
+                /* Stereo Headphone Class-specific
+                   AS Audio Data Endpoint Descriptor */
+                .extra = (uint8_t[]) {
+                    0x07,                       /*  u8  bLength */
+                    USB_DT_CS_ENDPOINT,         /*  u8  bDescriptorType */
+                    DST_EP_GENERAL,             /*  u8  bDescriptorSubtype */
+                    0x00,                       /*  u8  bmAttributes */
+                    0x00,                       /*  u8  bLockDelayUnits */
+                    U16(0x0000),                /* u16  wLockDelay */
+                },
+            },
+        }
+    },{
+        .bInterfaceNumber              = 1,
+        .bAlternateSetting             = ALTSET_51,
+        .bNumEndpoints                 = 1,
+        .bInterfaceClass               = USB_CLASS_AUDIO,
+        .bInterfaceSubClass            = USB_SUBCLASS_AUDIO_STREAMING,
+        .iInterface                    = STRING_REAL_STREAM,
+        .ndesc                         = 2,
+        .descs = (USBDescOther[]) {
+            {
+                /* Headphone Class-specific AS General Interface Descriptor */
+                .data = (uint8_t[]) {
+                    0x07,                       /*  u8  bLength */
+                    USB_DT_CS_INTERFACE,        /*  u8  bDescriptorType */
+                    DST_AS_GENERAL,             /*  u8  bDescriptorSubtype */
+                    0x01,                       /*  u8  bTerminalLink */
+                    0x00,                       /*  u8  bDelay */
+                    0x01, 0x00,                 /* u16  wFormatTag */
+                }
+            },{
+                /* Headphone Type I Format Type Descriptor */
+                .data = (uint8_t[]) {
+                    0x0b,                       /*  u8  bLength */
+                    USB_DT_CS_INTERFACE,        /*  u8  bDescriptorType */
+                    DST_AS_FORMAT_TYPE,         /*  u8  bDescriptorSubtype */
+                    0x01,                       /*  u8  bFormatType */
+                    0x06,                       /*  u8  bNrChannels */
+                    0x02,                       /*  u8  bSubFrameSize */
+                    0x10,                       /*  u8  bBitResolution */
+                    0x01,                       /*  u8  bSamFreqType */
+                    U24(USBAUDIO_SAMPLE_RATE),  /* u24  tSamFreq */
+                }
+            }
+        },
+        .eps = (USBDescEndpoint[]) {
+            {
+                .bEndpointAddress      = USB_DIR_OUT | 0x01,
+                .bmAttributes          = 0x0d,
+                .wMaxPacketSize        = USBAUDIO_PACKET_SIZE(6),
+                .bInterval             = 1,
+                .is_audio              = 1,
+                /* Stereo Headphone Class-specific
+                   AS Audio Data Endpoint Descriptor */
+                .extra = (uint8_t[]) {
+                    0x07,                       /*  u8  bLength */
+                    USB_DT_CS_ENDPOINT,         /*  u8  bDescriptorType */
+                    DST_EP_GENERAL,             /*  u8  bDescriptorSubtype */
+                    0x00,                       /*  u8  bmAttributes */
+                    0x00,                       /*  u8  bLockDelayUnits */
+                    U16(0x0000),                /* u16  wLockDelay */
+                },
+            },
+        }
+    },{
+        .bInterfaceNumber              = 1,
+        .bAlternateSetting             = ALTSET_71,
+        .bNumEndpoints                 = 1,
+        .bInterfaceClass               = USB_CLASS_AUDIO,
+        .bInterfaceSubClass            = USB_SUBCLASS_AUDIO_STREAMING,
+        .iInterface                    = STRING_REAL_STREAM,
+        .ndesc                         = 2,
+        .descs = (USBDescOther[]) {
+            {
+                /* Headphone Class-specific AS General Interface Descriptor */
+                .data = (uint8_t[]) {
+                    0x07,                       /*  u8  bLength */
+                    USB_DT_CS_INTERFACE,        /*  u8  bDescriptorType */
+                    DST_AS_GENERAL,             /*  u8  bDescriptorSubtype */
+                    0x01,                       /*  u8  bTerminalLink */
+                    0x00,                       /*  u8  bDelay */
+                    0x01, 0x00,                 /* u16  wFormatTag */
+                }
+            },{
+                /* Headphone Type I Format Type Descriptor */
+                .data = (uint8_t[]) {
+                    0x0b,                       /*  u8  bLength */
+                    USB_DT_CS_INTERFACE,        /*  u8  bDescriptorType */
+                    DST_AS_FORMAT_TYPE,         /*  u8  bDescriptorSubtype */
+                    0x01,                       /*  u8  bFormatType */
+                    0x08,                       /*  u8  bNrChannels */
+                    0x02,                       /*  u8  bSubFrameSize */
+                    0x10,                       /*  u8  bBitResolution */
+                    0x01,                       /*  u8  bSamFreqType */
+                    U24(USBAUDIO_SAMPLE_RATE),  /* u24  tSamFreq */
+                }
+            }
+        },
+        .eps = (USBDescEndpoint[]) {
+            {
+                .bEndpointAddress      = USB_DIR_OUT | 0x01,
+                .bmAttributes          = 0x0d,
+                .wMaxPacketSize        = USBAUDIO_PACKET_SIZE(8),
+                .bInterval             = 1,
+                .is_audio              = 1,
+                /* Stereo Headphone Class-specific
+                   AS Audio Data Endpoint Descriptor */
+                .extra = (uint8_t[]) {
+                    0x07,                       /*  u8  bLength */
+                    USB_DT_CS_ENDPOINT,         /*  u8  bDescriptorType */
+                    DST_EP_GENERAL,             /*  u8  bDescriptorSubtype */
+                    0x00,                       /*  u8  bmAttributes */
+                    0x00,                       /*  u8  bLockDelayUnits */
+                    U16(0x0000),                /* u16  wLockDelay */
+                },
+            },
+        }
+    }
+};
+
+static const USBDescDevice desc_device_multi = {
+    .bcdUSB                        = 0x0100,
+    .bMaxPacketSize0               = 64,
+    .bNumConfigurations            = 1,
+    .confs = (USBDescConfig[]) {
+        {
+            .bNumInterfaces        = 2,
+            .bConfigurationValue   = DEV_CONFIG_VALUE,
+            .iConfiguration        = STRING_CONFIG,
+            .bmAttributes          = USB_CFG_ATT_ONE | USB_CFG_ATT_SELFPOWER,
+            .bMaxPower             = 0x32,
+            .nif = ARRAY_SIZE(desc_iface_multi),
+            .ifs = desc_iface_multi,
+        }
+    },
+};
+
+static const USBDesc desc_audio_multi = {
+    .id = {
+        .idVendor          = USBAUDIO_VENDOR_NUM,
+        .idProduct         = USBAUDIO_PRODUCT_NUM,
+        .bcdDevice         = 0,
+        .iManufacturer     = STRING_MANUFACTURER,
+        .iProduct          = STRING_PRODUCT,
+        .iSerialNumber     = STRING_SERIALNUMBER,
+    },
+    .full = &desc_device_multi,
+    .str  = usb_audio_stringtable,
 };
 
 /*
@@ -300,10 +583,11 @@ struct streambuf {
     uint32_t cons;
 };
 
-static void streambuf_init(struct streambuf *buf, uint32_t size)
+static void streambuf_init(struct streambuf *buf, uint32_t size,
+                           uint32_t channels)
 {
     g_free(buf->data);
-    buf->size = size - (size % USBAUDIO_PACKET_SIZE);
+    buf->size = size - (size % USBAUDIO_PACKET_SIZE(channels));
     buf->data = g_malloc(buf->size);
     buf->prod = 0;
     buf->cons = 0;
@@ -315,21 +599,21 @@ static void streambuf_fini(struct streambuf *buf)
     buf->data = NULL;
 }
 
-static int streambuf_put(struct streambuf *buf, USBPacket *p)
+static int streambuf_put(struct streambuf *buf, USBPacket *p, uint32_t channels)
 {
     uint32_t free = buf->size - (buf->prod - buf->cons);
 
-    if (free < USBAUDIO_PACKET_SIZE) {
+    if (free < USBAUDIO_PACKET_SIZE(channels)) {
         return 0;
     }
-    if (p->iov.size != USBAUDIO_PACKET_SIZE) {
+    if (p->iov.size != USBAUDIO_PACKET_SIZE(channels)) {
         return 0;
     }
 
     usb_packet_copy(p, buf->data + (buf->prod % buf->size),
-                    USBAUDIO_PACKET_SIZE);
-    buf->prod += USBAUDIO_PACKET_SIZE;
-    return USBAUDIO_PACKET_SIZE;
+                    USBAUDIO_PACKET_SIZE(channels));
+    buf->prod += USBAUDIO_PACKET_SIZE(channels);
+    return USBAUDIO_PACKET_SIZE(channels);
 }
 
 static uint8_t *streambuf_get(struct streambuf *buf, size_t *len)
@@ -357,14 +641,15 @@ typedef struct USBAudioState {
         enum usb_audio_altset altset;
         struct audsettings as;
         SWVoiceOut *voice;
-        bool mute;
-        uint8_t vol[2];
+        Volume vol;
         struct streambuf buf;
+        uint32_t channels;
     } out;
 
     /* properties */
     uint32_t debug;
-    uint32_t buffer;
+    uint32_t buffer_user, buffer;
+    bool multi;
 } USBAudioState;
 
 #define TYPE_USB_AUDIO "usb-audio"
@@ -397,10 +682,15 @@ static int usb_audio_set_output_altset(USBAudioState *s, int altset)
 {
     switch (altset) {
     case ALTSET_OFF:
-        streambuf_init(&s->out.buf, s->buffer);
         AUD_set_active_out(s->out.voice, false);
         break;
-    case ALTSET_ON:
+    case ALTSET_STEREO:
+    case ALTSET_51:
+    case ALTSET_71:
+        if (s->out.channels != altset_channels[altset]) {
+            usb_audio_reinit(USB_DEVICE(s), altset_channels[altset]);
+        }
+        streambuf_init(&s->out.buf, s->buffer, s->out.channels);
         AUD_set_active_out(s->out.voice, true);
         break;
     default:
@@ -431,33 +721,33 @@ static int usb_audio_get_control(USBAudioState *s, uint8_t attrib,
 
     switch (aid) {
     case ATTRIB_ID(MUTE_CONTROL, CR_GET_CUR, 0x0200):
-        data[0] = s->out.mute;
+        data[0] = s->out.vol.mute;
         ret = 1;
         break;
     case ATTRIB_ID(VOLUME_CONTROL, CR_GET_CUR, 0x0200):
-        if (cn < 2) {
-            uint16_t vol = (s->out.vol[cn] * 0x8800 + 127) / 255 + 0x8000;
+        if (cn < USBAUDIO_MAX_CHANNELS(s)) {
+            uint16_t vol = (s->out.vol.vol[cn] * 0x8800 + 127) / 255 + 0x8000;
             data[0] = vol;
             data[1] = vol >> 8;
             ret = 2;
         }
         break;
     case ATTRIB_ID(VOLUME_CONTROL, CR_GET_MIN, 0x0200):
-        if (cn < 2) {
+        if (cn < USBAUDIO_MAX_CHANNELS(s)) {
             data[0] = 0x01;
             data[1] = 0x80;
             ret = 2;
         }
         break;
     case ATTRIB_ID(VOLUME_CONTROL, CR_GET_MAX, 0x0200):
-        if (cn < 2) {
+        if (cn < USBAUDIO_MAX_CHANNELS(s)) {
             data[0] = 0x00;
             data[1] = 0x08;
             ret = 2;
         }
         break;
     case ATTRIB_ID(VOLUME_CONTROL, CR_GET_RES, 0x0200):
-        if (cn < 2) {
+        if (cn < USBAUDIO_MAX_CHANNELS(s)) {
             data[0] = 0x88;
             data[1] = 0x00;
             ret = 2;
@@ -479,16 +769,17 @@ static int usb_audio_set_control(USBAudioState *s, uint8_t attrib,
 
     switch (aid) {
     case ATTRIB_ID(MUTE_CONTROL, CR_SET_CUR, 0x0200):
-        s->out.mute = data[0] & 1;
+        s->out.vol.mute = data[0] & 1;
         set_vol = true;
         ret = 0;
         break;
     case ATTRIB_ID(VOLUME_CONTROL, CR_SET_CUR, 0x0200):
-        if (cn < 2) {
+        if (cn < USBAUDIO_MAX_CHANNELS(s)) {
             uint16_t vol = data[0] + (data[1] << 8);
 
             if (s->debug) {
-                fprintf(stderr, "usb-audio: vol %04x\n", (uint16_t)vol);
+                fprintf(stderr, "usb-audio: cn %d vol %04x\n", cn,
+                        (uint16_t)vol);
             }
 
             vol -= 0x8000;
@@ -497,7 +788,7 @@ static int usb_audio_set_control(USBAudioState *s, uint8_t attrib,
                 vol = 255;
             }
 
-            s->out.vol[cn] = vol;
+            s->out.vol.vol[cn] = vol;
             set_vol = true;
             ret = 0;
         }
@@ -506,11 +797,14 @@ static int usb_audio_set_control(USBAudioState *s, uint8_t attrib,
 
     if (set_vol) {
         if (s->debug) {
-            fprintf(stderr, "usb-audio: mute %d, lvol %3d, rvol %3d\n",
-                    s->out.mute, s->out.vol[0], s->out.vol[1]);
+            int i;
+            fprintf(stderr, "usb-audio: mute %d", s->out.vol.mute);
+            for (i = 0; i < USBAUDIO_MAX_CHANNELS(s); ++i) {
+                fprintf(stderr, ", vol[%d] %3d", i, s->out.vol.vol[i]);
+            }
+            fprintf(stderr, "\n");
         }
-        AUD_set_volume_out(s->out.voice, s->out.mute,
-                           s->out.vol[0], s->out.vol[1]);
+        audio_set_volume_out(s->out.voice, &s->out.vol);
     }
 
     return ret;
@@ -603,7 +897,7 @@ static void usb_audio_handle_dataout(USBAudioState *s, USBPacket *p)
         return;
     }
 
-    streambuf_put(&s->out.buf, p);
+    streambuf_put(&s->out.buf, p, s->out.channels);
     if (p->actual_length < p->iov.size && s->debug > 1) {
         fprintf(stderr, "usb-audio: output overrun (%zd bytes)\n",
                 p->iov.size - p->actual_length);
@@ -645,6 +939,9 @@ static void usb_audio_unrealize(USBDevice *dev, Error **errp)
 static void usb_audio_realize(USBDevice *dev, Error **errp)
 {
     USBAudioState *s = USB_AUDIO(dev);
+    int i;
+
+    dev->usb_desc = s->multi ? &desc_audio_multi : &desc_audio;
 
     usb_desc_create_serial(dev);
     usb_desc_init(dev);
@@ -652,18 +949,35 @@ static void usb_audio_realize(USBDevice *dev, Error **errp)
     AUD_register_card(TYPE_USB_AUDIO, &s->card);
 
     s->out.altset        = ALTSET_OFF;
-    s->out.mute          = false;
-    s->out.vol[0]        = 240; /* 0 dB */
-    s->out.vol[1]        = 240; /* 0 dB */
+    s->out.vol.mute      = false;
+    for (i = 0; i < USBAUDIO_MAX_CHANNELS(s); ++i) {
+        s->out.vol.vol[i] = 240; /* 0 dB */
+    }
+
+    usb_audio_reinit(dev, 2);
+}
+
+static void usb_audio_reinit(USBDevice *dev, unsigned channels)
+{
+    USBAudioState *s = USB_AUDIO(dev);
+
+    s->out.channels      = channels;
+    if (!s->buffer_user) {
+        s->buffer = 32 * USBAUDIO_PACKET_SIZE(s->out.channels);
+    } else {
+        s->buffer = s->buffer_user;
+    }
+
+    s->out.vol.channels  = s->out.channels;
     s->out.as.freq       = USBAUDIO_SAMPLE_RATE;
-    s->out.as.nchannels  = 2;
+    s->out.as.nchannels  = s->out.channels;
     s->out.as.fmt        = AUDIO_FORMAT_S16;
     s->out.as.endianness = 0;
-    streambuf_init(&s->out.buf, s->buffer);
+    streambuf_init(&s->out.buf, s->buffer, s->out.channels);
 
     s->out.voice = AUD_open_out(&s->card, s->out.voice, TYPE_USB_AUDIO,
                                 s, output_callback, &s->out.as);
-    AUD_set_volume_out(s->out.voice, s->out.mute, s->out.vol[0], s->out.vol[1]);
+    audio_set_volume_out(s->out.voice, &s->out.vol);
     AUD_set_active_out(s->out.voice, 0);
 }
 
@@ -675,8 +989,8 @@ static const VMStateDescription vmstate_usb_audio = {
 static Property usb_audio_properties[] = {
     DEFINE_AUDIO_PROPERTIES(USBAudioState, card),
     DEFINE_PROP_UINT32("debug", USBAudioState, debug, 0),
-    DEFINE_PROP_UINT32("buffer", USBAudioState, buffer,
-                       32 * USBAUDIO_PACKET_SIZE),
+    DEFINE_PROP_UINT32("buffer", USBAudioState, buffer_user, 0),
+    DEFINE_PROP_BOOL("multi", USBAudioState, multi, false),
     DEFINE_PROP_END_OF_LIST(),
 };
 
@@ -689,7 +1003,6 @@ static void usb_audio_class_init(ObjectClass *klass, void *data)
     dc->props         = usb_audio_properties;
     set_bit(DEVICE_CATEGORY_SOUND, dc->categories);
     k->product_desc   = "QEMU USB Audio Interface";
-    k->usb_desc       = &desc_audio;
     k->realize        = usb_audio_realize;
     k->handle_reset   = usb_audio_handle_reset;
     k->handle_control = usb_audio_handle_control;