Many ACPI & Power Management Changes For Linux 3.18 Kernel
Written by Michael Larabel in Linux Kernel on 7 October 2014 at 08:26 AM EDT. Add A Comment
Rafael Wysocki sent out his first aligned set of changes of ACPI core and power management changes he's planning on volleying over to Linus Torvalds for the Linux 3.18 kernel merge window.

There's many ACPI/PM changes as usual per kernel cycle and they affect a few thousand lines of code (anticipated 3.18 merge window ACPI/PM pull: 130 files changed, 3968 insertions, 1528 deletions). Those curious about all of the ACPI/PM changes or if they have one of their issues fixed, you can see Rafael's mailing list post that is basically a pre-pull message to ensure all patches have been queued up.

Some notable changes from the pull include CPUfreq supporting per-policy driver data, ACPI properly supporting _OSI("Darwin"), and a generic CPU idle ARM64 driver. Matthew Garrett explained the Darwin OSI change for OS X hardware, "Apple hardware queries _OSI("Darwin") in order to determine whether the system is running OS X, and changes firmware behaviour based on the answer. The most obvious difference in behaviour is that Thunderbolt hardware is forcibly powered down unless the system is running OS X. The obvious solution would be to simply add Darwin to the list of supported _OSI strings, but this causes problems. Recent Apple hardware includes two separate methods for checking _OSI strings. The first will check whether Darwin is supported, and if so will exit. The second will check whether Darwin is supported, but will then continue to check for further operating systems. If a further operating system is found then later firmware code will assume that the OS is not OS X. This results in the unfortunate situation where the Thunderbolt controller is available at boot time but remains powered down after suspend."
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