CODEWITHSUNDEEP
linuxhidlibusb
sandun dhammika
sandun dhammika

Reputation: 921

Remove input driver bound to the HID interface

I'm playing with some driver code for a special kind of keyboard. And this keyboard does have special modes. According to the specification those modes could only be enabled by sending and getting feature reports.

I'm using 'hid.c' file and user mode to send HID reports. But both 'hid_read' and 'hid_get_feature_report' failed with error number -1.

I already tried detaching keyboard from kernel drivers using libusb, but when I do that, 'hid_open' fails. I guess this is due to that HID interface already using by 'input' or some driver by the kernel. So I may not need to unbind kernel hidraw driver, instead I should try unbinding the keyboard ('input') driver top of 'hidraw' driver. Am I correct?

And any idea how I could do that? And how to find what are drivers using which drivers and which low level driver bind to which driver?

Upvotes: 2

Views: 854

Answers (1)

sandun dhammika
sandun dhammika

Reputation: 921

I found the answer to this myself. The answer is to dig this project and find it's hid implementation on libusb. Or you could directly receive the report.

int HID_API_EXPORT hid_get_feature_report(hid_device *dev, unsigned char *data, size_t length)
{
    int res = -1;
    int skipped_report_id = 0;
    int report_number = data[0];

    if (report_number == 0x0) {
        /* Offset the return buffer by 1, so that the report ID
           will remain in byte 0. */
        data++;
        length--;
        skipped_report_id = 1;
    }
    res = libusb_control_transfer(dev->device_handle,
        LIBUSB_REQUEST_TYPE_CLASS|LIBUSB_RECIPIENT_INTERFACE|LIBUSB_ENDPOINT_IN,
        0x01/*HID get_report*/,
        (3/*HID feature*/ << 8) | report_number,
        dev->interface,
        (unsigned char *)data, length,
        1000/*timeout millis*/);

    if (res < 0)
        return -1;

    if (skipped_report_id)
        res++;

    return res;
}

I'm sorry I can't post my actual code due to some legal reasons. However the above code is from hidapi implementation.

So even you work with an old kernel , you still have the chance to make your driver working. This answers to this question too: https://stackoverflow.com/questions/30565999/kernel-version-2-6-32-does-not-support-hidiocgfeature

Upvotes: 1

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