今天幫ML裏的哥們試一個configfs的問題， 又重新認識了一下USB interface。原來，一個function可以有多個interface的，
以前一直認爲只有一個。看下面的cat /sys/kernel/debug/usb/devices 輸出。
T: Bus=01 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 3 Spd=480 MxCh= 0
D: Ver= 2.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS=64 #Cfgs= 1
P: Vendor=1d6b ProdID=0104 Rev= 4.07
S: Manufacturer=Foo Inc.
S: Product=Bar Gadget
S: SerialNumber=0123456789
C:* #Ifs= 5 Cfg#= 1 Atr=80 MxPwr= 2mA
A: FirstIf#= 0 IfCount= 3 Cls=01(audio) Sub=00 Prot=20
A: FirstIf#= 3 IfCount= 2 Cls=02(comm.) Sub=06 Prot=00
I:* If#= 0 Alt= 0 #EPs= 0 Cls=01(audio) Sub=01 Prot=20 Driver=snd-usb-audio
I:* If#= 1 Alt= 0 #EPs= 0 Cls=01(audio) Sub=02 Prot=20 Driver=snd-usb-audio
I: If#= 1 Alt= 1 #EPs= 1 Cls=01(audio) Sub=02 Prot=20 Driver=snd-usb-audio
E: Ad=01(O) Atr=05(Isoc) MxPS= 192 Ivl=1ms
I:* If#= 2 Alt= 0 #EPs= 0 Cls=01(audio) Sub=02 Prot=20 Driver=snd-usb-audio
I: If#= 2 Alt= 1 #EPs= 1 Cls=01(audio) Sub=02 Prot=20 Driver=snd-usb-audio
E: Ad=81(I) Atr=05(Isoc) MxPS= 192 Ivl=1ms
I:* If#= 3 Alt= 0 #EPs= 1 Cls=02(comm.) Sub=06 Prot=00 Driver=cdc_ether
E: Ad=83(I) Atr=03(Int.) MxPS= 16 Ivl=32ms
I: If#= 4 Alt= 0 #EPs= 0 Cls=0a(data ) Sub=00 Prot=00 Driver=cdc_ether
I:* If#= 4 Alt= 1 #EPs= 2 Cls=0a(data ) Sub=00 Prot=00 Driver=cdc_ether
E: Ad=82(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E: Ad=02(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
這個device是用configfs做成的，有audio 和NCM兩個function，一共5個interface （#Ifs= 5 ）
Audio有3個Interface， NCM有2個。看有幾個interface，不能只是看有幾個interface descriptor，
因爲，一個interface裏可能有AlternateSetting，這樣這個interface裏可能就有2個interface
descriptor。 上面打星號（*）就是當前使能的interface，可以看到interace #4，當前的setting就是
AlternateSetting。 當前使能的interface，就是最後用set_interface選擇的。看最下面catc的圖
lsusb的輸出
root@imx6qdlsolo:~# lsusb -d 1d6b:0104 -v
Bus 001 Device 004: ID 1d6b:0104 Linux Foundation Multifunction Composite Gadget
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 2.00
bDeviceClass 0
bDeviceSubClass 0
bDeviceProtocol 0
bMaxPacketSize0 64
idVendor 0x1d6b Linux Foundation
idProduct 0x0104 Multifunction Composite Gadget
bcdDevice 4.07
iManufacturer 1 Foo Inc.
iProduct 2 Bar Gadget
iSerial 3 0123456789
bNumConfigurations 1
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 298
bNumInterfaces 5
bConfigurationValue 1
iConfiguration 4 CDC ECM + audio
bmAttributes 0x80
(Bus Powered)
MaxPower 2mA
Interface Association:
bLength 8
bDescriptorType 11
bFirstInterface 0
bInterfaceCount 3
bFunctionClass 1 Audio
bFunctionSubClass 0
bFunctionProtocol 32
iFunction 5 Source/Sink
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 0
bAlternateSetting 0
bNumEndpoints 0
bInterfaceClass 1 Audio
bInterfaceSubClass 1 Control Device
bInterfaceProtocol 32
iInterface 6 Topology Control
AudioControl Interface Descriptor:
bLength 9
bDescriptorType 36
bDescriptorSubtype 1 (HEADER)
bcdADC 2.00
bCategory 8
wTotalLength 74
bmControl 0x00
AudioControl Interface Descriptor:
bLength 8
bDescriptorType 36
bDescriptorSubtype 10 (CLOCK_SOURCE)
bClockID 6
bmAttributes 0x01 Internal fixed Clock
bmControls 0x01
Clock Frequency Control (read-only)
bAssocTerminal 0
iClockSource 7 48000Hz
AudioControl Interface Descriptor:
bLength 8
bDescriptorType 36
bDescriptorSubtype 10 (CLOCK_SOURCE)
bClockID 5
bmAttributes 0x01 Internal fixed Clock
bmControls 0x01
Clock Frequency Control (read-only)
bAssocTerminal 0
iClockSource 8 48000Hz
AudioControl Interface Descriptor:
bLength 17
bDescriptorType 36
bDescriptorSubtype 2 (INPUT_TERMINAL)
bTerminalID 1
wTerminalType 0x0101 USB Streaming
bAssocTerminal 0
bCSourceID 5
bNrChannels 2
bmChannelConfig 0x00000003
Front Left (FL)
Front Right (FR)
bmControls 0x0003
Copy Protect Control (read/write)
iChannelNames 0
iTerminal 9 USBH Out
AudioControl Interface Descriptor:
bLength 17
bDescriptorType 36
bDescriptorSubtype 2 (INPUT_TERMINAL)
bTerminalID 2
wTerminalType 0x0200 Input Undefined
bAssocTerminal 0
bCSourceID 6
bNrChannels 2
bmChannelConfig 0x00000003
Front Left (FL)
Front Right (FR)
bmControls 0x0003
Copy Protect Control (read/write)
iChannelNames 0
iTerminal 10 USBD Out
AudioControl Interface Descriptor:
bLength 12
bDescriptorType 36
bDescriptorSubtype 3 (OUTPUT_TERMINAL)
bTerminalID 4
wTerminalType 0x0101 USB Streaming
bAssocTerminal 0
bSourceID 2
bCSourceID 6
bmControls 0x0003
Copy Protect Control (read/write)
iTerminal 11 USBH In
AudioControl Interface Descriptor:
bLength 12
bDescriptorType 36
bDescriptorSubtype 3 (OUTPUT_TERMINAL)
bTerminalID 3
wTerminalType 0x0300 Output Undefined
bAssocTerminal 0
bSourceID 1
bCSourceID 5
bmControls 0x0003
Copy Protect Control (read/write)
iTerminal 12 USBD In
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 1
bAlternateSetting 0
bNumEndpoints 0
bInterfaceClass 1 Audio
bInterfaceSubClass 2 Streaming
bInterfaceProtocol 32
iInterface 13 Playback Inactive
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 1
bAlternateSetting 1
bNumEndpoints 1
bInterfaceClass 1 Audio
bInterfaceSubClass 2 Streaming
bInterfaceProtocol 32
iInterface 14 Playback Active
AudioStreaming Interface Descriptor:
bLength 16
bDescriptorType 36
bDescriptorSubtype 1 (AS_GENERAL)
bTerminalLink 1
bmControls 0x00
bFormatType 1
bmFormats 0x00000001
PCM
bNrChannels 2
bmChannelConfig 0x00000003
Front Left (FL)
Front Right (FR)
iChannelNames 0
AudioStreaming Interface Descriptor:
bLength 6
bDescriptorType 36
bDescriptorSubtype 2 (FORMAT_TYPE)
bFormatType 1 (FORMAT_TYPE_I)
bSubslotSize 2
bBitResolution 16
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x01 EP 1 OUT
bmAttributes 5
Transfer Type Isochronous
Synch Type Asynchronous
Usage Type Data
wMaxPacketSize 0x00c0 1x 192 bytes
bInterval 4
AudioControl Endpoint Descriptor:
bLength 8
bDescriptorType 37
bDescriptorSubtype 1 (EP_GENERAL)
bmAttributes 0x00
bmControls 0x00
bLockDelayUnits 0 Undefined
wLockDelay 0
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 2
bAlternateSetting 0
bNumEndpoints 0
bInterfaceClass 1 Audio
bInterfaceSubClass 2 Streaming
bInterfaceProtocol 32
iInterface 15 Capture Inactive
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 2
bAlternateSetting 1
bNumEndpoints 1
bInterfaceClass 1 Audio
bInterfaceSubClass 2 Streaming
bInterfaceProtocol 32
iInterface 16 Capture Active
AudioStreaming Interface Descriptor:
bLength 16
bDescriptorType 36
bDescriptorSubtype 1 (AS_GENERAL)
bTerminalLink 4
bmControls 0x00
bFormatType 1
bmFormats 0x00000001
PCM
bNrChannels 2
bmChannelConfig 0x00000003
Front Left (FL)
Front Right (FR)
iChannelNames 0
AudioStreaming Interface Descriptor:
bLength 6
bDescriptorType 36
bDescriptorSubtype 2 (FORMAT_TYPE)
bFormatType 1 (FORMAT_TYPE_I)
bSubslotSize 2
bBitResolution 16
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 5
Transfer Type Isochronous
Synch Type Asynchronous
Usage Type Data
wMaxPacketSize 0x00c0 1x 192 bytes
bInterval 4
AudioControl Endpoint Descriptor:
bLength 8
bDescriptorType 37
bDescriptorSubtype 1 (EP_GENERAL)
bmAttributes 0x00
bmControls 0x00
bLockDelayUnits 0 Undefined
wLockDelay 0
Interface Association:
bLength 8
bDescriptorType 11
bFirstInterface 3
bInterfaceCount 2
bFunctionClass 2 Communications
bFunctionSubClass 6 Ethernet Networking
bFunctionProtocol 0
iFunction 21 CDC ECM
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 3
bAlternateSetting 0
bNumEndpoints 1
bInterfaceClass 2 Communications
bInterfaceSubClass 6 Ethernet Networking
bInterfaceProtocol 0
iInterface 18 CDC Ethernet Control Model (ECM)
CDC Header:
bcdCDC 1.10
CDC Union:
bMasterInterface 3
bSlaveInterface 4
CDC Ethernet:
iMacAddress 19 de3cab45bb77
bmEthernetStatistics 0x00000000
wMaxSegmentSize 1514
wNumberMCFilters 0x0000
bNumberPowerFilters 0
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x83 EP 3 IN
bmAttributes 3
Transfer Type Interrupt
Synch Type None
Usage Type Data
wMaxPacketSize 0x0010 1x 16 bytes
bInterval 9
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 4
bAlternateSetting 0
bNumEndpoints 0
bInterfaceClass 10 CDC Data
bInterfaceSubClass 0
bInterfaceProtocol 0
iInterface 0
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 4
bAlternateSetting 1
bNumEndpoints 2
bInterfaceClass 10 CDC Data
bInterfaceSubClass 0
bInterfaceProtocol 0
iInterface 20 CDC Ethernet Data
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x82 EP 2 IN
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0200 1x 512 bytes
bInterval 0
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x02 EP 2 OUT
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0200 1x 512 bytes
bInterval 0
Device Qualifier (for other device speed):
bLength 10
bDescriptorType 6
bcdUSB 2.00
bDeviceClass 0
bDeviceSubClass 0
bDeviceProtocol 0
bMaxPacketSize0 64
bNumConfigurations 1
can't get debug descriptor: Resource temporarily unavailable
Device Status: 0x0001
Self Powered
Catc的picture
