Power Management For Linux 3.20: SFI CPUFreq, Skylake P-State, New AMD ACPI Driver

Written by Michael Larabel in Linux Kernel on 11 February 2015 at 09:11 AM EST. Add A Comment
Rafael Wysocki sent in another hearty ACPI+PM pull request for the next revision to the Linux kernel.

First up, the ACPI and power management pull request for Linux 3.20 has a new SFI CPUfreq driver. SFI is short for the Simple Firmware Interface and is a way of firmware to expose static tables to the operating system. SFI was devised by Intel and initially supported by their Moorestown platform. SFI has been supported by the Linux kernel for some time while this new driver is for reading the SFI tables for CPUfreq and works with hardware like the Intel Atom Z34xx and Z35xx SoCs.

Another big Intel change for Linux 3.20 is Skylake support within the P-State scaling driver. There's also been other fixes and improvements to this commonly used Intel CPU frequency scaling driver.

On the AMD side there's a new ACPI driver for AMD SoCs that is similar to Intel's LPSS low-power subsystem driver. The AMD ACPI2Platform device support is for the upcoming Carrizo APUs and newer. Ken Xue at AMD did the work, "This new feature is to interpret AMD specific ACPI device to platform device such as I2C, UART found on AMD CZ and later chipsets. It is based on example INTEL LPSS. Now, it can support AMD I2C & UART."

There's also core ACPI / ACPICA updates and fixes, ACPI-based IOAPIC hotplug support, CPUFreq core fixes, a new Tegra Activity Monitor devfreq driver, and other assorted work. More details on the ACPI / power management changes for Linux 3.20 can be found via this pull request.
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