Linux To Allow Limiting Tiger Lake SoC PL4 Package Maximum Power Limit
The Power Limit4 (PL4) support allows limiting the SoC's maximum power limit at a package level. The user can mandate the maximum Wattage the SoC is allowed in order to prevent power spikes from tripping any power adapter, battery over-current protection, or other limitations.
The user can control the PL4 power limit in Watts via the RAPL (Runtime Average Power Limiting) sysfs interface. RAPL has already allowed power limiting while this PL4 support is about providing the limit at a package-level.
The PL4 support for Linux is just being enabled at this time for the upcoming Tiger Lake SoCs. It looks like this feature may potentially work for prior SoCs, but for lack of testing this is just being enabled for Tiger Lake at this time.
The patch providing this Linux PowerCap PL4 support is currently in the power management "bleeding-edge" Git branch while still has time to be queued for "-next" ahead of Linux 5.9.