Re: [PATCH 0/3] ACPI: platform_profile: fix legacy sysfs with multiple handlers

[Mario Limonciello <mario.limonciello@amd.com>]

On 2/24/2025 13:50, Antheas Kapenekakis wrote:
> 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?).

To me this raises a fundamental question.  What is really different 
between quiet and low-power?  quiet just affects fan curves and 
low-power affects power?

One could argue that changing power will indirectly affect fan performance.

Because it makes me wonder if we really should just make them permanent 
aliases.

> 
> The problem stems from the fact that asus-wmi uses quiet, and amd-pmf uses
> low-power. While it is not clear to me what the amd-pmf module is supposed
> to do here, and perhaps some autodetection should be done and make it bail,
> if we assume it should be kept, then there is a small refactor that is
> needed to maintain the existing ABI interface.
> 
> This is the subject of this patch series.
> 
> Essentially, we introduce the concept of a "secondary" handler. Secondary
> handlers work exactly the same, except for the fact they are able to
> receive all profile names through the sysfs interface. The expectation
> here would be that the handlers choose the closest appropriate profile
> they have, and this is what I did for the amd-pmf handler.
> 
> In their own platform_profile namespace, these handlers still work normally
> and only accept the profiles from their probe functions, with -ENOSUP for
> the rest.
> 
> In the absence of a primary handler, the options of all secondary handlers
> are unioned in the legacy sysfs, which prevents them from hiding each
> other's options.
> 
> With this patch series applied, the sysfs interface will look like this:
> 
> $ 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 (3):
>    ACPI: platform_profile: Add support for secondary handlers
>    ACPI: platform_profile: add all options to amd-pmf as a secondary
>      handler
>    ACPI: platform_profile: Do not hide options missing in secondary
>      handlers
> 
>   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   |  7 ++++
>   4 files changed, 67 insertions(+), 8 deletions(-)
>