Michael Larabel of Phoronix reports that FreeBSD developers have figured out temperature monitoring on the AMD Zen/Ryzen processor. You may also see a detailed bug report from the FreeBSD mailing list below.
While Linux users of AMD’s new Zen-based Ryzen/Threadripper/Epyc processors are still waiting for thermal driver support to hit the mainline Linux kernel, FreeBSD developers have already managed to produce the Zen “Family 17h” CPU thermal monitoring support on their own.

From this FreeBSD bug report, developers have managed to get the AMD CPU temperature monitoring working for Zen processors under Linux with their existing temperature driver.

Original post: http://www.phoronix.com/scan.php?page=news_item&px=AMD-Zen-FreeBSD-Temps
FreeBSD Bugzilla:  https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=218264
Discussion: https://www.phoronix.com/forums/forum/software/bsd-mac-os-x-hurd-others/974991-freebsd-developers-tackle-amd-zen-ryzen-temperature-monitoring-before-linux