Intel Has 50 Patches For ACPI/Power In Linux 3.3

The fun for the Linux 3.3 kernel merge window is not over quite yet; Intel this morning published 50 patches for integration into this next Linux kernel that affect ACPI and power management, primarily around ACPI 5.0 support for the Linux kernel.

The 50 patches for the 3.3 pull were submitted by Len Brown, the Intel OSTC developer who is also the ACPI sub-system maintainer for the Linux kernel. These new patches were largely authored by him and other Intel engineers, among others.

Among the notable changes in the ACPI pull is much work on ACPI 5.0, Turbostat support for Intel Ivy Bridge, a more robust Intel idle driver (especially for systems dealing with KVM virtualization), ACPICA (ACPI Component Architecture) updates, and APEI (ACPI Platform Error Interface) updates. From patch 20 for ACPICA, "this version contains full support for the ACPI 5.0 specification." There's also a fix that will allow some new motherboards (select P67/H67/Z68 motherboards) that can suspend but are not able to wake-up on Linux 3.2 and earlier, to now wake-up properly.

ACPI 5.0 support improvements under Linux 3.3 include supporting FADT version 5, implementing the hardware-reduced option, a new interface for drivers to access AML mutex objects, support for all new resource descriptors, and other new functionality of the ACPI 5.0 specification. The ACPI 5.0 specification was published in November of 2011. Per the change-log spec on ACPI 5.0, reduced hardware support is described as "allows for ACPI systems without the usual ACPI hardware. This support is enabled by a flag in the revision 5 FADT. If it is set, ACPICA will not attempt to initialize or use any of the usual ACPI hardware." New tables define by ACPI 5.0 include the boot graphics resource, dynamic root of trust for measurement, firmware performance data, generic timer description, memory power state, platform communications channel, platform memory topology, and RAS feature table. There also other ACPI 5.0 changes as mentioned in the aforelinked spec. The Advanced Configuration and Power Interface 5.0 specification in full can be downloaded from acpi.info.

With the ACPI 5.0 specification being only a few months old, ACPI 5.0 hardware isn't yet widespread, but more hardware is certainly coming. With new products around the Intel Ivy Bridge launch will likely be an onslaught of motherboards targeting the ACPI 5.0 specification. With the Linux 3.3 kernel this support is obviously bettered, but now out of reach for the Ubuntu 12.04 LTS and its Linux 3.2 kernel, unless the support is (unlikely) back-ported to the stable branch. This would mean there's now risk of power-related issues under Ubuntu 12.04 LTS for new hardware, beyond the graphics worries, but we'll wait and see how it plays out.

The ACPI / power management patch series for the Linux 3.3 kernel can be found on the kernel mailing list. Linux 3.3 is shaping up quite nicely with many new features (see the Linux 3.3 articles for details) and just a little bit of time left to the merge window.

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