Yet I can still not read CPU core temperatures of my ryzen 2600 on Linux (5.0-rc2). I am not sure what is going on but I think next time I'll go with Intel again. I read this may be related to some NDA by AMD but not sure.
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?...
I've had a Ryzen 1700 since they first came out so I was following the Linux support for that fairly closely at the time, mostly by browsing Phoronix fairly frequently. Thankfully after a few months I didn't need to because things were working pretty well by then, other than the thermal monitoring that took quite a while to land. Linux and brand new hardware rarely seem to get along well regardless of the vendor unfortunately.
It could be a nice way to learn a tool like Binary Ninja or IDA (pro).
It's probably some DeviceIoControl call. Once you know the call 12-bit (I think?) ID from userland code, it should be relatively straightforward to follow the driver code to see where it ends up and what hardware registers it uses.
Or maybe it's just something through ACPI?