AMD P-State Fixes & Other Power Management Changes For Linux 6.6

The ACPI and power management updates were merged last week for the Linux 6.6 kernel.

The Linux 6.5 kernel cycle was notable in that AMD P-State EPP "active" is the default for modern Ryzen systems moving forward over ACPI CPUFreq. After that default change in Linux 6.5 and other big AMD P-State additions in prior kernels, for Linux 6.6 on the AMD side it's mostly about fixing a few bugs from the increased amd-pstate exposure. The Intel P-State driver has also seen some fixes for the Linux 6.6 merge window.

The ACPI and power management updates for Linux 6.6 aren't especially exciting but still some of the fixes are worthwhile. Highlights on the power management side include:

- Improvements to the TEO CPU idle code by Rafael Wysocki to significantly reduce the number of cases where the governor requests stopping the tick when the selected idle state is shallow. Wysocki mentioned this rework to avoid calling tick_nohz_get_sleep_length() too often as it's likely to become quite expensive (time consuming) moving forward.

- A fix to the amd-pstate-ut code to avoid a possible kernel panic when loading the driver.

- A fix to the amdp-state-ut code to return the correct highest_perf value. Due to platforms supporting AMD Preferred Core handling, the amd-pstate-ut driver to this point didn't return a properly handled value.

- The cpupower utility that lives within the Linux kernel source tree has added turbo boost support and other new AMD P-State features.

- An Intel P-State fix over incorrect CPU frequencies reported since Linux 5.18+.

- A rework to the hibernation memory snapshotting to avoid storing pages filled with zeroes in the hibernation image files. This was observed by Google engineers on Chrome OS of having many zero pages stored in the hibernation image file, in some cases 2GB+ of zero filled pages or ~36% of the overall image file size.

- Various other fixes and clean-ups.

More details on the power management changes for Linux 6.6 via this pull.

Wysocki also submitted the ACPI changes for Linux 6.6 that include ACPICA code updates, a backlight=native mode DMI quirk for Apple iMac12,1 and iMac12,2 devices, LoongArch fixes, an ACPI thermal driver clean-up, and other fixes.