ACPI Support Continues To Be Improved In Linux

There's a number of ACPI updates that are being shown off and will likely make their debut in the Linux 3.9 kernel for improving the power management support.

Support for the Advanced Configuration and Power Interface (ACPI) continues to see improvements with each succeeding Linux kernel release and it's getting into shape compared to Microsoft Windows' support for the device configuration and power management specification. The Linux kernel is also seeing less power regressions recently and power consumption levels under Linux are generally doing well compared to Windows.

In the past few days there's been a number of ACPI-patches being presented on the Linux kernel mailing list, most (if not all) should then appear in the Linux 3.9 kernel.

ACPI / PM: Export power states of ACPI devices via sysfs - Rafael Wysocki is making it possible for user-space scripts/applications to easily find out the current power state of a given device with ACPI power management through sysfs. "Make it possible to retrieve the current power state of a device with ACPI power management from user space via sysfs by adding a new attribute power_state to the sysfs directory associated with the struct acpi_device object representing the device's ACPI node."

ACPI / PM: Export power resources information to user space - This patch-set from Rafael builds upon the earlier mentioned patch, but for exposing more ACPI power resources to user-space, namely via sysfs.

acpi-cpufreq and powernow-k8 fixes - There's a set of six patches to take care of fixes for acpi-cpufreq and powernow-k8. What's worthy of being pointed out with these patches is they come from Borislav Petkov. Boris is a long-time Linux kernel developer who was responsible for much of AMD's Linux kernel contributions, but he was laid off last October when AMD got rid of some Linux kernel developers and closed their Operating System Research Center. While Petkov is no longer employed by AMD, he's still working on areas of the kernel that benefit the company. (Upon some research, it looks like he might now be employed by SUSE.)

ACPI / PM: Initial power state checking and power state setting changes - More power management work by Rafael. These four patches "make the determination of the initial device power state more robust and change the way ACPI device power states are changed to be more in line with the spec."

PCI, ACPI: pci root bus hotplug support / pci match_driver - Kernel improvements for hot-plugging and hot-remove are coming thanks to work by Yinghai Lu.

ACPI / PM: Fixes related to the D3cold power state - Two D3cold power state fixes.

These are just the notable ACPI / power management work that's been shown off in the past week on the Linux kernel mailing list.