There is a comment in drivers/input/evdev.c which says:
/* EV_SYN==0 is EV_CNT, _not_ SYN_CNT, see EVIOCGBIT */
That is, EVIOCGBIT(0, ...) should return a bit mask with supported
event types instead of SYN_* event codes.
* defs.h (evdev_ev): New prototype.
* evdev.c: Include "xlat/evdev_ev.h" and remove "xlat/evdev_sync.h".
(bit_ioctl) <case EV_SYN>: Replace EV_SYN with 0, use evdev_ev
with XT_SORTED in decode_bitset invocation instead.
* ioctl.c: Do not include "xlat/evdev_ev.h".
(evdev_decode_number): Print nr == 0x20 as "0" instead of "EV_SYN".
* tests/ioctl_evdev.c (main): Use 0 instead of EV_SYN in EVIOCGBIT
output.
* xlat/evdev_sync.in: Remove.
Co-Authored-by: Dmitry V. Levin <ldv@altlinux.org> Fixes: v4.10~89 "Add decoding for evdev ioctls"