The eventfd_signal() function is the equivalent to a write to an eventfd file descriptor: it bumps the internal counter and wakes up processes waiting for it.
eventfd_signal() is meant to be used by kernel drivers. DRM drivers will call it through linuxkpi.
This is a requirement to the following patch to drm-kmod:
https://github.com/freebsd/drm-kmod/pull/358
Sponsored by: The FreeBSD Foundation