Increase "Report Count" limit in HID descriptor parser

[wulf]

Summary

Increase "Report Count" value limit in HID descriptor parser from 255 to 256 to fix usage/report size calculation of Microsoft`s "Touch Hardware Quality Assurance" certificate blob[1] found in many touchscreens.

Some devices like WaveShare touchscreens require reading of THQA report at initialization stage to start event generation so it would be nice to provide usbd_req_get_report() with proper report length. Also it should fix infamous "hid_get_item: Number of items(256) truncated to 255" boot message.

It may make sense to bump the limit to 1k or even more to fix e.g. some gaming keyboards HID-descriptor parsing[2]

While here, join several "c->flags = dval" lines in to single line.

[1] https://docs.microsoft.com/en-us/windows-hardware/design/component-guidelines/touch-and-pen-support
[2] https://unix.stackexchange.com/questions/401722/new-trueos-install-keyboard-doesnt-work-right

Test Plan

Attach touchscreen and see "hid_get_item: Number of items(256) truncated to 255" warning gone.

[• hselasky]

Looks good! Maybe you should bump the __FreeBSD_version due to changing a structure size. What about MFC-ing?

[• hselasky]

Did you check that enumerating loops of loc.count use a 32-bit variable aswell. I'm not sure if there are any such in the kernel.

[wulf]

Maybe you should bump the __FreeBSD_version due to changing a structure size.

No need. hid_data is private structure

What about MFC-ing?

Will do

Did you check that enumerating loops of loc.count use a 32-bit variable aswell. I'm not sure if there are any such in the kernel.

All existing in-tree drivers except wmt(4) use hid_locate() wrapper which is still artificially limited to 255 usages of the same type with defining of "index" input parameter as uint8_t. As these drivers call hid_locate() with index=0 or index=1 only, I see no reason to break KPI with extending the limit just now. Internally hid_locate() uses 32-bit variables so possible growth of number of returned usages should not do any harm.