AMD SB-TSI Sensor Driver Set To Appear With Linux 5.11

There are a lot of changes coming with Linux 5.11 and on the AMD side includes the likes of VanGogh and Dimgrey Cavefish graphics support, AMD EPYC Zen 3 support in the AMD_Energy driver, AMD RAPL Zen1/Zen2/Zen3 PowerCap support, an AMD SoC PMC driver, and the AMD Sensor Fusion Hub driver for Ryzen laptops is finally being mainlined... Another new addition was queued up this weekend by way of hwmon-next and that's the AMD SB-TSI sensor driver.

Going back to early in 2020 we reported on Google engineers working on this AMD SB-TSI code for the Sideband Temperature Sensor Interface. This is about reading the AMD SoC temperature connected to a BMC.

SB-TSI has been part of the public AMD Zen documentation while thanks to Google in cooperation with AMD there is this SB-TSI temperature sensor support coming.

SB Temperature Sensor Interface (SB-TSI) is an SMBus compatible interface that reports AMD SoC's Ttcl (normalized temperature), and resembles a typical 8-pin remote temperature sensor's I2C interface to BMC.

This commit adds basic support using this interface to read CPU temperature, and read/write high/low CPU temp thresholds.

The sbtsi_temp driver is added as part of the hardware monitoring "hwmon" code set to go into the kernel once the merge window opens for Linux 5.11, which will be as soon as tomorrow if no additional Linux 5.10 release candidate is warranted later today. This documentation covers more details on this sideband temperature monitoring interface for those interested.

The Linux kernel already supports the AMD Zen CPU temperature monitoring via the k10temp driver. This "sbtsi_temp" driver work will likely be useful for the likes of OpenBMC for temperature monitoring. It should come as little surprise at this stage and given our past articles, but AMD has been working to improve their OpenBMC support and acknowledge the growing customer interest in open-source firmware stacks.