usb.core.Device.detach_kernel_driver() could unbind TinyUSB class drivers

[samblenny]

The current implementation of usb.core.Device.detach_kernel_driver() looks like this:

void common_hal_usb_core_device_detach_kernel_driver(usb_core_device_obj_t *self, mp_int_t interface) {
    #if CIRCUITPY_USB_KEYBOARD_WORKFLOW
    usb_keyboard_detach(self->device_address, interface);
    #endif
}

So, it's only aware of the possibility of the CircuitPython core having claimed keyboards.

For better compatibility with desktop PyUSB, the detach implementation could be extended to unbind TinyUSB class drivers. For more about TinyUSB class driver binding, check out the enum_parse_configuration_desc() implementation in tinyusb/src/host/usbh.c.

It's not clear to me at the moment whether TinyUSB provides a way to unbind drivers independently of removing a device. See process_removed_device() implementation in usbh.c for how undbinding works during device removal.

[samblenny]

An alternate approach would be to upstream a new TinyUSB configuration option to disable its class drivers since CircuitPython doesn't use them. Doing it that way might save a fair chunk of code space in the firmware image.

[edit: no, actually that's not a viable idea because the supervisor uses the hub and HID class drivers for keyboard input]

[samblenny]

As I read more of the code, it seems like CircuitPython actually uses the Hub and HID class drivers to implement the supervisor's HID keyboard input feature. But, as far as I can tell:

1. No other class drivers are enabled
2. The usb_keyboard_detach() function is a bit of a misnomer because it actually controls the TinyUSB HID driver. So, it's not limited to just keyboards

If I read the code correctly, common_hal_usb_core_device_detach_kernel_driver() should actually be working just fine to unbind all the enabled TinyUSB class drivers that aren't hubs (only HID and Hub are enabled).

So, basically, the premise of this issue was probably wrong. I now think that detach_kernel_driver() should work fine for HID gamepads and mice. Gonna close this.