T480S Heads firmware lack ACPI P-state tables.

[James333666999]

Without commit 91173, T480S systems running Heads firmware lack ACPI P-state tables. This primarily affects:

Xen hypervisor frequency scaling (the original reported issue)
Operating systems that rely on ACPI _PSS/_PCT/_PPC tables for CPU power management

outlined here: https://ticket.coreboot.org/issues/623
Fix availble: https://review.coreboot.org/c/coreboot/+/91173

[tlaurion]

Pr would have been welcome.

From https://review.coreboot.org/c/coreboot/+/91173, see download. Option "Format Patch" shows command line:
git fetch https://review.coreboot.org/coreboot refs/changes/73/91173/2 && git format-patch -1 --stdout FETCH_HEAD

To create additional patch for coreboot 25.09, patches are under patches/coreboot-25.09/, we we need to redirect to last patch+1 name with proper description.

cd ~
git clone https://github.com/linuxboot/heads
cd heads
./docker_repro.sh make BOARD=EOL_t480s-maximized
cd build/x86/coreboot-25.09/
git fetch https://review.coreboot.org/coreboot refs/changes/73/91173/2 && git format-patch -1 --stdout FETCH_HEAD > ../../../patches/coreboot-25.09/0013-sklkbl_thinkpad-Enable_ACPI_P-state_table_generation.patch
cd ~/heads
./docker_repro.sh make BOARD=EOL_t480s-maximized real.remove_canary_files-extract_patch_rebuild_what_changed
./docker_repro.sh make BOARD=EOL_t480s-maximized
[...]
INFO: Applying patch file: patches/coreboot-25.09/0013-sklkbl_thinkpad-Enable_ACPI_P-state_table_generation.patch
Checking patch build/x86/coreboot-25.09/src/mainboard/lenovo/sklkbl_thinkpad/devicetree.cb...
Applied patch build/x86/coreboot-25.09/src/mainboard/lenovo/sklkbl_thinkpad/devicetree.cb cleanly.
[...]

Test rom