Temperature monitoring for the first gen Ryzen chips has been in the kernel for about a year. The patch for second gen is there but narrowly missed the 5.0 release window, so it should land in the first release after 5.0.

Intel is a bit faster about this but it's not like they have perfect day 1 kernel support either. i.e. temperature monitoring drivers for both first gen Ryzen and Coffee Lake landed in 4.15. At the time Ryzen was almost a year old and Coffee Lake was about half a year old.

http://lkml.iu.edu/hypermail/linux/kernel/1811.0/01237.html?...