Intel's Newest Linux Driver Is For Radio Frequency Interference Mitigation
Intel's RFIM INT340X thermal driver is for Radio Frequency Interference Mitigation. This driver is used for tweaking the fully integrated voltage regulator (FIVR) and DDR frequencies in order to avoid radio frequency interference with WiFi and 5G wireless.
For modern laptops and other small form factor devices using Intel SoCs, this driver can have the SoC's integrated voltage regulator switch frequencies by a small percent to avoid the noise harmonic interference with 5G/WiFi. The driver can tweak the IVR operation just enough that it doesn't interfere but without impacting the performance of the voltage regulator.
The driver also changes the DDR data rates if there is strong radio frequency interference from the memory. This functionality though is toggled by the BIOS on supported systems as "real-time DDR RFI mitigation" or similarly named option.
The new RFIM Linux driver exposes new FIVR and DVFS features via sysfs for tuning this behavior by Linux user-space. At least for now this RFIM driver appears to only support current Intel Tiger Lake and future Alder Lake hardware.
This RFIM driver has been queued into the thermal-next code ahead of the Linux 5.11 merge window. This thermal pull is also introducing the support for Intel workload hints for INT340X thermal/power tuning.