Win10 compatibility.

[perlindgren]

There seems to be some compatibility issue with Win10 and the generated descriptor(s).

#[gen_hid_descriptor(
    (collection = APPLICATION, usage = 0x01, usage_page = 0xff00) = {
        #[item_settings data] data=input;
    }
)]

#[allow(dead_code)]
struct Data {
    data: u8,
}

The generated descriptor looks like this.

data [
    0x6, 0x0, 0xff,      // USEGE PAGE Vendor
    0x9, 0x1,             // USAGE Vendor
    0xa1, 0x1,           // Collection (Application)
    0x15, 0x0,          // Logical minimum
    0x26, 0xff, 0x0,   // Logical maximum
    0x75, 0x8,          // Report size 8
    0x95, 0x1,          // Report count 1
    0x81, 0x0,          // Input
    0xc0,                 // End application collection
]

This works well under Linux (tested under arch) and OSX. Hower under Win10 the device is not properly detected/configured (USB Device Viewer shows the descriptors correctly but claims the devic to be in low power state.

Adding a usage before Input solves the issue.

data [
    0x6, 0x0, 0xff,      // USEGE PAGE Vendor
    0x9, 0x1,             // USAGE Vendor
    0xa1, 0x1,           // Collection (Application)
    0x15, 0x0,          // Logical minimum
    0x26, 0xff, 0x0,   // Logical maximum
    0x75, 0x8,          // Report size 8
    0x95, 0x1,          // Report count 1
    0x09, 0x01,        // USAGE Vendor <---- manually added here
    0x81, 0x0,          // Input
    0xc0,                 // End application collection
]

Either MS is out of specs (the wrapping usage should be inherited) or Linux/OSX just playing nice guessing, not sure.

Maybe there is already some workaround for this problem that I missed. If not, perhaps a syntax extension to the #[item_settings usage = 0x01, ...] would be possible. Or maybe let the proc macro always emit inherited usage from the wrapping collection (in this case).

Admittedly I'm a USB novice, so not sure what's best here. /Per