Re: OOPS after connection Droids MuIn USB display

[Erik Slagter]

Yeah, I've found it!

As I mentioned earlier, the device appears to have a control interface 
and no data interface. The current usb cdc-acm code doesn't account for 
this and so yields a oops because data_interface is null.

I've "fixed" it very dirtily by changing these lines:

if (call_interface_num > 0) {
    dev_dbg(&intf->dev, "No union descriptor, using call management 
descriptor\n");
data_interface = usb_ifnum_to_if(usb_dev, (data_interface_num = 
call_interface_num));

into:

if (call_interface_num > 0) {
    dev_dbg(&intf->dev, "No union descriptor, using call management 
descriptor\n");
data_interface = usb_ifnum_to_if(usb_dev, 0);

I can't give an exact patch because the source is full of added debug 
printk's now ;-)

As far as I understand it, this change results in data_interface to be 
set equal to control_interface and later on this gets dealed with properly.

And now it not only no longer oopses, it actually works!

If you're planning to make a quirk of it, the USB ID is 04d8:000b 
"Microchip Technology, Inc. PIC18F2550 (32K Flashable 10 Channel, 10 Bit 
A/D USB Microcontroller"

lsusb says:

Bus 002 Device 018: ID 04d8:000b Microchip Technology, Inc. PIC18F2550 
(32K Flashable 10 Channel, 10 Bit A/D USB Microcontroller)
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass            2 Communications
  bDeviceSubClass         2 Abstract (modem)
  bDeviceProtocol         1 AT-commands (v.25ter)
  bMaxPacketSize0        64
  idVendor           0x04d8 Microchip Technology, Inc.
  idProduct          0x000b PIC18F2550 (32K Flashable 10 Channel, 10 
Bit A/D USB Microcontroller)
  bcdDevice            0.00
  iManufacturer           1 DROIDS
  iProduct                2 VCOM
  iSerial                 0
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength           53
    bNumInterfaces          1
    bConfigurationValue     1
    iConfiguration          0
    bmAttributes         0xa0
      (Bus Powered)
      Remote Wakeup
    MaxPower              500mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           3
      bInterfaceClass         2 Communications
      bInterfaceSubClass      2 Abstract (modem)
      bInterfaceProtocol      1 AT-commands (v.25ter)
      iInterface              0
      CDC Header:
        bcdCDC               1.10
      CDC Call Management:
        bmCapabilities       0x01
          call management
        bDataInterface          1
      CDC ACM:
        bmCapabilities       0x06
          sends break
          line coding and serial state
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x83  EP 3 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0008  1x 8 bytes
        bInterval              10
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x84  EP 4 IN
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0040  1x 64 bytes        bInterval 
      10
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x04  EP 4 OUT
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0040  1x 64 bytes
        bInterval              10
Device Status:     0x0001
  Self Powered

Thanks.

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