DIMM Temperature Driver & PECI-CPUTemp Updated For Sapphire Rapids

Consulting firm 9elements sent out a set of patches this week to the peci-cputemp and dimmtemp drivers for supporting Intel Sapphire Rapids platforms, including for the up to eight socket configuration capable this generation.

While Intel Xeon Scalable "Sapphire Rapids" (SPR) already works with the long-used coretemp driver, one of the patches adds SPR support to the peci-cputemp driver. PECI-CPUTemp as a reminder provides digital thermal sensor readings of the CPU package and CPU cores that can then be accessed via the PECI (Platform Environment Control Interface) interface. This provides a lot of information to the hardware monitoring (HWMON) subsystem from Tthrottle, Tcontrol, Tjmax, and more information. Surprisingly Intel hadn't gotten to Sapphire Rapids support for peci-cputemp but now thanks to 9elements that should soon change upstream.

The other change is enabling Sapphire Rapids support for the PECI dimmtemp driver for reporting DDR5 DIMM memory temperatures. With Sapphire Rapids able to handle up to eight CPUs and each with 16 DIMMs, the dimmtemp driver had to be updated since at present can only handle up to 32 DIMMs in total. 9elements was able to go as far as verifying the DIMM Temperature driver for Linux can at least work for a four socket Sapphire Rapids system with 64 DIMMs present.

These new PECI hardware monitoring improvements for Sapphire Rapids are now out for review on the kernel mailing list and will likely be picked up in time for the v6.6 kernel cycle.