AMD CPU "k10temp" Linux Driver Updated To Report Negative Temperatures

The AMD k10temp Linux driver is used for CPU temperature reporting with all modern AMD Ryzen/EPYC processors plus going back all the way to many earlier FX / Athlon / Sempron / Opteron / Phenom CPUs starting with the Family 10h line-up. While this driver has been in the Linux kernel for years, it's carried a limitation until now that it can't handle reporting negative temperatures. That is changing thanks to new patches from AMD.

Due to trivial if statements, Tctl and Tdie temperatures less than zero have been reset to zero. Presumably this was done on the basis of imagining such negative temperature readings are inaccurate. However, in certain cases like extreme overclocking with liquid nitrogen and select industrial applications and the like, negative temperatures are possible.

This patch from AMD engineer Baskaran Kannan updates the k10temp driver to allow negative temperatures by dropping the prior "if less than zero" checks.

I was quite curious myself why AMD is working on negative temperature support for Linux... No, they aren't doing some wild LN2 overclocking or catering to some Linux enthusiasts. Rather, the patch notes that "there are industrial processors which work below zero." Presumably said industrial Linux users encountered this bug though the AMD patch doesn't note the specific industrial applications enjoying sub-zero AMD-powered Linux systems.

Given the simplicity of the patch, it should get picked up for the Linux 6.5 merge window if not earlier as a fix for the ongoing v6.4 cycle.