A Bit Late: Linux PCH Temperature Support Mistakenly Missing From The Intel C620 Series

While Intel is normally very punctual with their Linux hardware support and ensure that the full capabilities of the hardware are exposed under Linux, especially when it comes to server and workstation hardware, occasionally oversights are made.

The latest blemish is a Linux user discovering that the PCH temperature reading support wasn't there for his workstation with a Lewisburg C620 series chipset running dual Xeon Gold CPUs. The Intel C620 series have been around for more than three years and used by Skylake-SP / Cascade Lake SP. For being found with the original Xeon Scalable processors it's a bit surprising that missing PCH temperature monitoring support went unnoticed this long, but for the Linux 5.11 kernel that will see its stable release in early 2021 that issue has been corrected.

Andres Freund noted that while the chipset temperature sensor support was missing on Linux, the datasheet for Lewisburg matched the existing Intel PCH thermal driver support.

Thus after three years, adding the 0xA1B1 ID and the other basic additions to the intel_pch_thermal driver support, the temperature sensor is now working. The patch is just nine lines of new code to which Andres concluded with the patch message, "I suspect there's some other PCI IDs missing. But I hope somebody at Intel would have an easier time figuring that out than I..."

This Lewisburg addition to intel_pch_thermal is currently within the thermal-next code until the Linux 5.11 merge window.