Two years ago [1]the AMD Linux CPU temperature driver was updated to handle negative temperature reporting . That's for some users with exotic cooling systems and then also use within some industrial applications where the systems may be subject to sub-zero temperatures. The AMD sbtsi_temp driver is also now being similarly updated for handling freezing CPU temperatures.

The sbtsi_temp Linux driver is for the Sideband Interface (SBI) temperature sensor interface (SB-TSI). The AMD Sideband Interface is predominantly used for EPYC server processors and other select AMD SoCs. While the AMD k10temp CPU driver has already supported the expanded/negative temperature range, sbtsi_temp is only seeing that similar support now and is set to be merged for the upcoming Linux 6.18 cycle.

[2]

Cisco engineer Chuande Chen was the one working out this AMD CPU extended temperature range support for sbtsi_temp. Chuande explained with [3]the driver patch :

"Many AMD CPUs can support this feature now. We would get a wrong CPU DIE temperature if don't consider this. In low-temperature environments, the CPU die temperature can drop below zero. So many platforms would like to make extended temperature range as their default configuration.

Default temperature range (0C to 255.875C).

Extended temperature range (-49C to +206.875C).

Ref Doc: AMD V3000 PPR (Doc ID #56558)."

The engineer didn't elaborate on Cisco's low-temperature deployments of EPYC hardware. In any case this patch is queued up in the hardware monitoring "HWMON" subsystem's "hwmon-next" branch. Now that the patch is there it should be submitted as part of the Linux 6.18 kernel merge window in October and in turn will be out in stable form come December.



[1] https://www.phoronix.com/news/AMD-k10temp-Negative-Temps

[2] https://www.phoronix.com/image-viewer.php?id=2025&image=amd_ryzen_frozen_lrg

[3] https://git.kernel.org/pub/scm/linux/kernel/git/groeck/linux-staging.git/commit/?h=hwmon-next&id=612ecee07edcf235627b7c82a67a0fe4a2f61d13