[BUG] Redmi Book Pro 16 2024: platform_profile exposes unsupported performance modes on 7.1.x

Hello,

I am testing Linux kernel support on a Xiaomi Redmi Book Pro 16 2024
(TM2309) with an Intel Core Ultra 7 155H (Meteor Lake).

I believe there is a problem/regression in the platform_profile
handling on the 7.1.x Arch kernel.

Hardware:

Laptop: Xiaomi Redmi Book Pro 16 2024
Model: TM2309
CPU: Intel Core Ultra 7 155H (Meteor Lake)
BIOS: RMAMT6B0P0B0B
BIOS date: 06/10/2025

I reproduced the behavior on Linux 7.1.7 and again after updating to
Linux 7.1.8.

Kernel versions tested:

Linux 7.1.7-arch1-1
Linux 7.1.8-arch1-3

Reference kernel:

Linux 6.18.44-1-lts

The important difference is that Linux 7.1.x registers a
platform_profile interface and exposes four profiles, but two of those
profiles cannot actually be written.

On Linux 7.1.8-arch1-3:

$ uname -r
7.1.8-arch1-3

$ cat /sys/firmware/acpi/platform_profile
balanced

$ cat /sys/firmware/acpi/platform_profile_choices
low-power balanced balanced-performance performance

Testing the available profiles:

$ echo low-power | sudo tee /sys/firmware/acpi/platform_profile
low-power

$ cat /sys/firmware/acpi/platform_profile
low-power

This works.

$ echo balanced | sudo tee /sys/firmware/acpi/platform_profile
balanced

$ cat /sys/firmware/acpi/platform_profile
balanced

This also works.

However:

$ echo balanced-performance | sudo tee /sys/firmware/acpi/platform_profile
balanced-performance
tee: /sys/firmware/acpi/platform_profile: Operation not supported

The profile remains:

$ cat /sys/firmware/acpi/platform_profile
balanced

The same happens with performance:

$ echo performance | sudo tee /sys/firmware/acpi/platform_profile
performance
tee: /sys/firmware/acpi/platform_profile: Operation not supported

$ cat /sys/firmware/acpi/platform_profile
balanced

Therefore the advertised profiles are:

Works:
- low-power
- balanced

Fails:
- balanced-performance
- performance

power-profiles-daemon detects the platform_profile backend on 7.1.8:

$ powerprofilesctl

  performance:
    CpuDriver:  intel_pstate
    PlatformDriver:     platform_profile
    Degraded:   no

* balanced:
    CpuDriver:  intel_pstate
    PlatformDriver:     platform_profile

  power-saver:
    CpuDriver:  intel_pstate
    PlatformDriver:     platform_profile

Attempting to activate performance through power-profiles-daemon
consequently fails because the underlying platform_profile write
returns -EOPNOTSUPP.

The same behavior was already present on Linux 7.1.7.

Important comparison with Linux 6.18.44-1-lts:

$ uname -r
6.18.44-1-lts

On the LTS kernel:

$ ls -l /sys/firmware/acpi/platform_profile*
ls: cannot access '/sys/firmware/acpi/platform_profile*': No such file
or directory

Neither platform_profile nor platform_profile_choices is exposed
through /sys/firmware/acpi.

However, the relevant kernel modules are present:

$ lsmod | grep -E "redmi|wmi|platform_profile|processor_thermal"

processor_thermal_soc_slider
platform_profile
redmi_wmi
...

The platform_profile module is present:

$ modinfo platform_profile

filename:
/lib/modules/6.18.44-1-lts/kernel/drivers/acpi/platform_profile.ko.zst

srcversion:
1286B64F09D8B6244885873

The processor thermal SoC slider module is also present:

$ modinfo processor_thermal_soc_slider

filename:
/lib/modules/6.18.44-1-lts/kernel/drivers/thermal/intel/int340x_thermal/processor_thermal_soc_slider.ko.zst

srcversion:
583E680621918305EF374CD

The Redmi WMI driver is present on both kernels, but has different
source versions:

Linux 6.18.44:

filename:
/lib/modules/6.18.44-1-lts/kernel/drivers/platform/x86/redmi-wmi.ko.zst

srcversion:
369C9F3502463ADD78FDC0F

Linux 7.1.8:

filename:
/lib/modules/7.1.8-arch1-3/kernel/drivers/platform/x86/redmi-wmi.ko.zst

srcversion:
E64350B38255B1100E64863

On both kernels the system is correctly identified:

DMI:
XIAOMI Redmi Book Pro 16 2024/TM2309
BIOS RMAMT6B0P0B0B 06/10/2025

The Redmi WMI device is also detected:

input: Redmibook WMI keys

There are no obvious redmi_wmi errors in dmesg.

The relevant kernel configuration is enabled on the LTS kernel:

CONFIG_ACPI=y
CONFIG_ACPI_PLATFORM_PROFILE=m
CONFIG_X86_INTEL_PSTATE=y

The platform_profile module is therefore available on LTS, but no
/sys/firmware/acpi/platform_profile interface is registered there.

This makes the 7.1.x behavior particularly interesting: the newer
kernel registers a platform_profile interface and advertises four
modes, but performance and balanced-performance return -EOPNOTSUPP
when written.

My questions are:

1. Is this expected behavior for the Redmi Book Pro 16 2024, or should
unsupported platform profiles be filtered out instead of being exposed
through platform_profile_choices?

2. Could this be related to changes in:
   - drivers/platform/x86/redmi-wmi.c
   - drivers/thermal/intel/int340x_thermal/processor_thermal_soc_slider.c
   - drivers/acpi/platform_profile.c
   - the platform_profile registration/selection logic
   - ACPI platform profile handling

3. Why does the 7.1.x kernel expose the platform_profile interface on
this machine while 6.18.44 does not, despite platform_profile and
processor_thermal_soc_slider being present on the LTS kernel?

4. Is there a known regression or intended behavior change between
these kernel versions that could explain this?

For reference, the ACPI errors seen during boot are unrelated-looking
USB _PLD/_UPC errors involving the RUCC method:

ACPI Error: Missing argument(s) for method [RUCC]
AE_AML_TOO_FEW_ARGUMENTS

These errors occur on both kernels and do not appear to be directly
related to platform_profile.

I can provide complete dmesg output, kernel configuration, ACPI
tables, or perform a git bisect if that would help identify the
change.

Thank you.
Martiya Aryan Mehr