On Friday, January 13, 2012 12:16:51 Andy Walls wrote:

Hans Verkuil [off-list ref] wrote:

quoted

Hi!

I've made a video4linux driver for the USB Keene FM Transmitter. See:

http://www.amazon.co.uk/Keene-Electronics-USB-FM-Transmitter/dp/B003GCHPDY/ref=sr_1_1?ie=UTF8&qid=1326450476&sr=8-1

The driver code is here:

http://git.linuxtv.org/hverkuil/media_tree.git/shortlog/refs/heads/keene

Unfortunately this device has exactly the same USB ID as the Logitech
AudioHub
USB speaker (http://www.logitech.com/en-us/439/3503).

The AudioHub has HID support for volume keys, but the FM transmitter
needs
a custom V4L2 driver instead.

I've attached the full lsusb -v output of both devices, but this is the
diff of
the two:

$ diff keene.txt audiohub.txt -u

--- keene.txt   2012-01-13 11:10:48.265399953 +0100
+++ audiohub.txt        2012-01-13 11:09:45.185398935 +0100

@@ -1,5 +1,5 @@

-Bus 007 Device 009: ID 046d:0a0e Logitech, Inc. 
+Bus 003 Device 004: ID 046d:0a0e Logitech, Inc. 

Device Descriptor:
  bLength                18
  bDescriptorType         1

@@ -12,7 +12,7 @@
  idProduct          0x0a0e 
  bcdDevice            1.00
  iManufacturer           1 HOLTEK 
-  iProduct                2 B-LINK USB Audio  
+  iProduct                2 AudioHub Speaker
  iSerial                 0 
  bNumConfigurations      1
  Configuration Descriptor:

@@ -22,9 +22,8 @@
    bNumInterfaces          3
    bConfigurationValue     1
    iConfiguration          0 
-    bmAttributes         0xa0
+    bmAttributes         0x80
      (Bus Powered)
-      Remote Wakeup
    MaxPower              500mA
    Interface Descriptor:
      bLength                 9

@@ -152,7 +151,7 @@
          bCountryCode            0 Not supported
          bNumDescriptors         1
          bDescriptorType        34 Report
-          wDescriptorLength      22
+          wDescriptorLength      31
         Report Descriptors: 
           ** UNAVAILABLE **
      Endpoint Descriptor:

As you can see, the differences are very small.

In my git tree I worked around it by adding the USB ID to the ignore
list
if the Keene driver is enabled, and ensuring that the Keene driver is
disabled by default.

But is there a better method to do this? At least the iProduct strings
are
different, is that something that can be tested in hid-core.c?

Regards,

Hans

Maybe it doesn't matter, but what do the Report Descriptors look like?

http://www.slashdev.ca/2010/05/08/get-usb-report-descriptor-with-linux/

Attached the new lsusb outputs, this time with the report descriptor.

Note that if I plug in the Keene transmitter, then no input device is
created:

Jan 13 14:25:12 tschai kernel: [ 1686.020166] usb 7-4: new full-speed USB device number 3 using ohci_hcd
Jan 13 14:25:12 tschai kernel: [ 1686.248735] generic-usb 0003:046D:0A0E.0009: hiddev0,hidraw4: USB HID v1.10 Device [HOLTEK  B-LINK USB Audio  ] on usb-0000:00:16.0-4/input2

Compare that to what happens when the audiohub is plugged in:

Jan 13 14:25:49 tschai kernel: [ 1722.820125] usb 3-4: new high-speed USB device number 6 using ehci_hcd
Jan 13 14:25:49 tschai kernel: [ 1722.973529] hub 3-4:1.0: USB hub found
Jan 13 14:25:49 tschai kernel: [ 1722.973960] hub 3-4:1.0: 4 ports detected
Jan 13 14:25:49 tschai kernel: [ 1723.250629] usb 3-4.4: new full-speed USB device number 7 using ehci_hcd
Jan 13 14:25:49 tschai kernel: [ 1723.390888] input: HOLTEK  AudioHub Speaker as /devices/pci0000:00/0000:00:16.2/usb3/3-4/3-4.4/3-4.4:1.2/input/input12
Jan 13 14:25:49 tschai kernel: [ 1723.391176] generic-usb 0003:046D:0A0E.000A: input,hidraw4: USB HID v1.10 Device [HOLTEK  AudioHub Speaker] on usb-0000:00:16.2-4.4/input2

I'm no expert on usb and HID, so I hope someone can point me to a better solution.

Regards,

	Hans