[PATCH v2 0/2] ACPI: platform_profile: fix legacy sysfs with multiple handlers

[Antheas Kapenekakis <lkml@antheas.dev>]

On the Asus Z13 (2025), a device that would need the amd-pmf quirk that
was removed on the platform_profile refactor, we see the following output
from the sysfs platform profile:

$ cat /sys/firmware/acpi/platform_profile_choices
balanced performance

I.e., the quiet profile is missing. Which is a major regression in terms of
power efficiency and affects both tuned, and ppd (it also affected my
software but I fixed that on Saturday). This would affect any laptop that
loads both amd-pmf and asus-wmi (around 15 models give or take?) and only
get worse in 2025, as more laptops start to integrate amd-pmf.

The problem stems from the fact that wmi handlers use different
profiles than amd-pmf, which can load alongside them, and block their
choices. This patch series is a mitigation of this issue, by making pmf
accept all profiles through the legacy sysfs, and by making it a secondary
handler.

While we can argue about whether the secondary handler concept is
necessary, alternatives such as renaming profiles in current drivers will
break existing scripts that are tested for a particular manufacturer, and
allowing amd-pmf override options may cause unforseen regressions in
other wmi drivers.

+CC Luke

Changelog since V1:
    - merge patches 1 and 3 as per Rafael
    - simplify secondary comment about secondary and make it last

Behavior with this patch applied and asus-wmi, amd-pmf
(maintains interop with 6.13):

$ cat /sys/firmware/acpi/platform_profile_choices
quiet balanced performance

And writing quiet to it results in the profile being applied to both
platform profile handlers.

$ echo low-power > /sys/firmware/acpi/platform_profile
bash: echo: write error: Operation not supported
$ echo quiet > /sys/firmware/acpi/platform_profile
$ cat /sys/class/platform-profile/platform-profile-*/{name,profile}
asus-wmi
amd-pmf
quiet
quiet

Agreed ABI still works:
$ echo quiet > /sys/class/platform-profile/platform-profile-0/profile
$ echo quiet > /sys/class/platform-profile/platform-profile-1/profile
bash: echo: write error: Operation not supported
$ echo low-power > /sys/class/platform-profile/platform-profile-0/profile
bash: echo: write error: Operation not supported
$ echo low-power > /sys/class/platform-profile/platform-profile-1/profile

Antheas Kapenekakis (2):
  ACPI: platform_profile: Add handlers that do not occlude power options
  ACPI: platform_profile: make amd-pmf a secondary handler

 drivers/acpi/platform_profile.c    | 57 +++++++++++++++++++++++++-----
 drivers/platform/x86/amd/pmf/spc.c |  3 ++
 drivers/platform/x86/amd/pmf/sps.c |  8 +++++
 include/linux/platform_profile.h   |  5 +++
 4 files changed, 65 insertions(+), 8 deletions(-)

-- 
2.48.1