I am building an USB adapter for an old game controller. So far everything is working fine. My HID descriptor looks like this:
0x05, 0x01, /* USAGE_PAGE (Generic Desktop) */
0x09, 0x05, /* USAGE (Game Pad) */
0xa1, 0x01, /* COLLECTION (Application) */
0xa1, 0x03, /* COLLECTION (Report) */
0x85, 0x01, /* REPORT_ID (1) */
0x05, 0x09, /* USAGE_PAGE (Button) */
0x19, 0x01, /* USAGE_MINIMUM (Button 1) */
0x29, 0x0e, /* USAGE_MAXIMUM (Button 14) */
0x15, 0x00, /* LOGICAL_MINIMUM (0) */
0x25, 0x01, /* LOGICAL_MAXIMUM (1) */
0x95, 0x0e, /* REPORT_COUNT (14) */
0x75, 0x01, /* REPORT_SIZE (1) */
0x81, 0x02, /* INPUT (Data,Var,Abs) */
0x95, 0x01, /* REPORT_COUNT (1) */
0x75, 0x02, /* REPORT_SIZE (2) */
0x81, 0x03, /* INPUT (Cnst) */
0xa1, 0x00, /* COLLECTION (Physical) */
0x05, 0x01, /* USAGE_PAGE (Generic Desktop) */
0x09, 0x30, /* USAGE (X) */
0x09, 0x31, /* USAGE (Y) */
0x15, 0x00, /* LOGICAL_MINIMUM (0) */
0x25, 0x64, /* LOGICAL_MAXIMUM (100) */
0x75, 0x08, /* REPORT_SIZE (8) */
0x95, 0x02, /* REPORT_COUNT (2) */
0x81, 0x02, /* INPUT (Data,Var,Abs) */
0xc0, /* END_COLLECTION */
0xc0, /* END_COLLECTION */
0xc0 /* END_COLLECTION */
Now I want to add support for up to 4 of these controllers. If I understand the
HID spec correctly, one way to do this is to repeat the descriptor 4 times, each time with a different report ID. (I know I could probably just have multiple USB interfaces with the HID class, but I'd rather not do it that way; my USB code would get a great deal more complicated.)
When I tried this Linux refused to recognize the device as a gamepad. The HID
driver (hid-generic) is loaded, and the descriptor seems to be parsed correctly, but there is no device file in /dev/input/.
EDIT:
I tested my code on Windows 7, and it looks like this problem is indeed Linux specific. So I am reformulating my original question:
How do I need to modify my HID descriptor, so it works on both Windows and Linux?
When plugging the device in, dmesg reports this:
usb 3-6: new low-speed USB device number 8 using xhci_hcd
usb 3-6: ep 0x81 - rounding interval to 64 microframes, ep desc says 80 microframes
input: XYZ Adapter as /devices/pci0000:00/0000:00:14.0/usb3/3-6/3-6:1.0/0003:16C0:05DC.0009/input/input20
hid-generic 0003:16C0:05DC.0009: input,hidraw4: USB HID v1.01 Gamepad [XYZ Adapter] on usb-0000:00:14.0-6/input0
This is identical to what it says when plugging in the working 1-controller version. The device appears in lsusb, with the correct IDs/descriptors.
Best Answer
After some hours of poking around in debugfs and the kernel sources, I figured it out.
As it turns out the descriptor was fine, the problem was that udev (for whatever reason) decided the create the device file with root-only access. After fixing this, my device now appears as a 56-button 8-axis gamepad, which is not quite what I wanted, but still close enough.