The Linux hardware monitoring “k10temp” driver drops support for reporting CPU voltage and current information for AMD Zen-based processors due to a lack of documentation to properly support the functionality.
Earlier in 2020, this long-standing AMD hwmon temperature driver added support for core / SoC current and voltage reporting with Zen processors based on the work of the community and some best assumptions around correct registers. But now that support is being dropped due to a lack of accuracy in some configurations and the possibility that it could even damage the hardware.
Last week the main hwmon pull request was for the Linux 5.11 cycle, while it was sent today as a secondary update with the only change being the removal of this k10temp current / voltage reporting.
The backing is removed as it turns out [it] was not worth the effort. ”
The actual Git commit removing k10temp support further explains:
Voltages and currents are reported by Zen CPUs. However, the way to do this is not documented, changes from CPU to CPU and the raw data is not calibrated. Calibration information is available, but again not documented. This results in a less than perfect user experience, to the concern that loading the driver could potentially damage the hardware (by reporting voltages out of range). Effective support for voltage and current reporting is not sustainable. Let drop.
For those who just want power stats, the “AMD_Energy” driver is also available with the main kernel, but at the moment only power details are displayed on EPYC CPUs after initial Ryzen support was eliminated there. Hopefully AMD will publish the necessary documentation in 2021 so that this k10temp support can be properly restored.