浅析usbhid中usbhid_fixup_report_descriptor修正知名报告描述符错误

hid_probe
==>usb_hid_configure
==*>hid_get_class_descriptor(dev, interface->desc.bInterfaceNumber, HID_DT_REPORT, rdesc, rsize) 读取鼠标或键盘的报告描述符report descriptor简写为rdesc
==*>usbhid_fixup_report_descriptor(le16_to_cpu(dev->descriptor.idVendor),
            le16_to_cpu(dev->descriptor.idProduct), rdesc,
            rsize, rdesc_quirks_param);
// usbhid_fixup_report_descriptor函数
// 描述该vid+pid的report descriptor是否在rdesc黑名单里边,
// 如果在,那么该硬件产品存在报告描述符知名bug,使用hid_rdesc_blacklist和
// insmod usbhid.ko rdesc_quirks=vid:pid:quirks驱动插入时动态提供的rdesc_quirks_param修正数组中的[luther.gliethtp]
// 正确数值替换hid_get_class_descriptor读取到rdesc内存中的错误数值
// rdesc_quirks_param所有数值都在/sys/module/usbhid/parameters/rdesc_quirks文件中[luther.gliethtp]
/**
 * usbhid_fixup_report_descriptor: check if report descriptor needs fixup
 *
 * Description:
 *    Walks the hid_rdesc_blacklist[] array and checks whether the device
 *    is known to have broken report descriptor that needs to be fixed up
 *    prior to entering the HID parser
 *
 * Returns: nothing
 */
void usbhid_fixup_report_descriptor(const u16 idVendor, const u16 idProduct,
                    char *rdesc, unsigned rsize, char **quirks_param)
{
    int n, m;
    u16 paramVendor, paramProduct;
    u32 quirks;

    /* static rdesc quirk entries */
    for (n = 0; hid_rdesc_blacklist[n].idVendor; n++)
        if (hid_rdesc_blacklist[n].idVendor == idVendor &&
                hid_rdesc_blacklist[n].idProduct == idProduct)
            __usbhid_fixup_report_descriptor(hid_rdesc_blacklist[n].quirks,
                    rdesc, rsize);

    /* runtime rdesc quirk entries handling */
    for (n = 0; quirks_param[n] && n < MAX_USBHID_BOOT_QUIRKS; n++) {
        m = sscanf(quirks_param[n], "0x%hx:0x%hx:0x%x",
                ¶mVendor, ¶mProduct, &quirks);

        if (m != 3)
            printk(KERN_WARNING
                "Could not parse HID quirk module param %s\n",
                quirks_param[n]);
        else if (paramVendor == idVendor && paramProduct == idProduct)
            __usbhid_fixup_report_descriptor(quirks, rdesc, rsize);
    }

}