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Hugh Blemings's Blog, A Diary and Miscellaneous ramblings

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Detaching Kernel Drivers w/libusb

Done some tinkering with libusb this last week or so in order to get the USBmicro boards that Jeremy and I bought going.

More on the reason for the tinkering later but in the process I discovered the kernels HID driver happily seizes the device on plugin - not unreasonable as the device identifies itself as a HID device.

After unsuccessfully going down the route of trying to tell the kernel HID driver to ignore it, I found that libusb has a couple of functions that are intended to deal with this very situation.

It may be poor reading of the docs or search skills on my part, but I wasn't able to find a definitive reference on how to actually use them, so here's the sequence that worked for me, edited for brevity:

    struct usb_bus          *bus_list;
    struct usb_device       *dev = NULL;
    struct usb_dev_handle   *handle;


        /* Look for the first u4xx device we can find then try and open */
    if((dev = find_u4xx(bus_list)) == NULL) {
        return NULL; 
    }

        /* Try and get a handle to the device */
    if((handle = usb_open(dev)) == NULL) {
        return NULL;
    }

        /* The kernel's HID driver will seize the USBMicro device as it
           says it's a HID device - we need to tell the kernel to 
           let go of it */
    if (usb_detach_kernel_driver_np(handle, 0) < 0) {
          /* If this fails, usually just means that no kernel driver
             had attached itself to the device so just ignore/warn */
    }
    
        /* Set the configuration */
    if(usb_set_configuration(handle, 1) != 0) {
        usb_close(handle);
        return NULL;
    }
  
        /* Clain interface - gather would need to this for each
           interface if the device has more than one */
    if (usb_claim_interface(handle, 0) != 0) {
        usb_close(handle);
        return NULL;
    }

    /* etc. etc. */

I'll post the actual code shortly, want to clean it up a wee bit first. It'll end up here but I'll post to that effect when it's up.

[/hacking] permanent link