[PATCH v1 4/4] platform profile: Document firmware-independent profile selection

[Daniel Lezcano]

Describe the firmware-neutral aggregate interface, retained ACPI
compatibility paths and unchanged device-based provider API. Document
hidden choices, mixed profiles and the sequential application of
aggregate writes.

Correct the per-provider attribute reference and extend existing ACPI
maintainer coverage to the extracted core and its interfaces.

Assisted-by: OpenCode:gpt-6.1-sol
Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxxxxxxxx>
---
 .../ABI/testing/sysfs-class-platform-profile  |  2 +-
 .../ABI/testing/sysfs-kernel-platform_profile | 30 ++++++++++++++
 .../ABI/testing/sysfs-platform_profile        |  7 +++-
 .../userspace-api/sysfs-platform_profile.rst  | 41 ++++++++++++++-----
 MAINTAINERS                                   |  6 +++
 include/linux/platform_profile.h              |  3 ++
 6 files changed, 77 insertions(+), 12 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-kernel-platform_profile

diff --git a/Documentation/ABI/testing/sysfs-class-platform-profile b/Documentation/ABI/testing/sysfs-class-platform-profile
index fcab26894ec3..75e0f6e2c128 100644
--- a/Documentation/ABI/testing/sysfs-class-platform-profile
+++ b/Documentation/ABI/testing/sysfs-class-platform-profile
@@ -35,7 +35,7 @@ Date:		March 2025
 KernelVersion:	6.14
 Description:	Reading this file gives the current selected profile for this
 		device. Writing this file with one of the strings from
-		platform_profile_choices changes the profile to the new value.
+		choices changes the profile to the new value.
 
 		This file can be monitored for changes by polling for POLLPRI,
 		POLLPRI will be signaled on any changes, independent of those
diff --git a/Documentation/ABI/testing/sysfs-kernel-platform_profile b/Documentation/ABI/testing/sysfs-kernel-platform_profile
new file mode 100644
index 000000000000..c64a175873e2
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-kernel-platform_profile
@@ -0,0 +1,30 @@
+What:		/sys/kernel/platform_profile/choices
+Date:		October 2026
+Description:	Space-separated list of standard profiles supported across all
+		registered platform profile providers. Profile names have the
+		meanings documented in sysfs-class-platform-profile.
+
+		The file is read-only and is present while at least one provider
+		is registered. Reading fails with EINVAL when providers have no
+		common choices. Hidden choices may contribute to the common
+		choices when multiple providers are registered; with a single
+		provider only its visible choices are listed.
+
+What:		/sys/kernel/platform_profile/profile
+Date:		October 2026
+Description:	Reading returns the current profile when all providers agree,
+		or "custom" when they have different profiles or a provider
+		reports a custom configuration.
+
+		Writing a profile listed in choices applies it to all providers.
+		"custom" cannot be written. Changes are applied sequentially;
+		an error does not roll back providers already updated.
+
+		The file is read-write and is present while at least one provider
+		is registered. It can be monitored with poll() for POLLPRI.
+		Notifications cover successful userspace writes and changes
+		reported by providers, for example after a firmware hotkey event.
+
+		On ACPI systems this interface shares its state with the legacy
+		/sys/firmware/acpi/platform_profile interface. The interface is
+		also available without ACPI support or with ACPI disabled.
diff --git a/Documentation/ABI/testing/sysfs-platform_profile b/Documentation/ABI/testing/sysfs-platform_profile
index 125324ab53a9..ee32e222af64 100644
--- a/Documentation/ABI/testing/sysfs-platform_profile
+++ b/Documentation/ABI/testing/sysfs-platform_profile
@@ -2,6 +2,8 @@ What:		/sys/firmware/acpi/platform_profile_choices
 Date:		October 2020
 Contact:	Hans de Goede <hdegoede@xxxxxxxxxx>
 Description:	This file contains a space-separated list of profiles supported for this device.
+		This is the ACPI compatibility interface for the system-wide
+		/sys/kernel/platform_profile/choices attribute.
 
 		Drivers must use the following standard profile-names:
 
@@ -23,7 +25,10 @@ Description:	This file contains a space-separated list of profiles supported for
 What:		/sys/firmware/acpi/platform_profile
 Date:		October 2020
 Contact:	Hans de Goede <hdegoede@xxxxxxxxxx>
-Description:	Reading this file gives the current selected profile for this
+Description:	This interface shares its state with
+		/sys/kernel/platform_profile/profile.
+
+		Reading this file gives the current selected profile for this
 		device. Writing this file with one of the strings from
 		platform_profile_choices changes the profile to the new value.
 
diff --git a/Documentation/userspace-api/sysfs-platform_profile.rst b/Documentation/userspace-api/sysfs-platform_profile.rst
index 6613e188242a..37b98e5075db 100644
--- a/Documentation/userspace-api/sysfs-platform_profile.rst
+++ b/Documentation/userspace-api/sysfs-platform_profile.rst
@@ -1,6 +1,8 @@
-=====================================================================
-Platform Profile Selection (e.g. /sys/firmware/acpi/platform_profile)
-=====================================================================
+.. SPDX-License-Identifier: GPL-2.0
+
+==========================
+Platform Profile Selection
+==========================
 
 On modern systems the platform performance, temperature, fan and other
 hardware related characteristics are often dynamically configurable. The
@@ -15,6 +17,21 @@ operation or towards performance.
 The purpose of the platform_profile attribute is to offer a generic sysfs
 API for selecting the platform profile of these automatic mechanisms.
 
+The framework is independent of the firmware interface used by a provider.
+Drivers can implement profile selection using ACPI, an embedded controller,
+or another platform-specific mechanism. The core does not discover providers
+or interpret firmware descriptions.
+
+The system-wide interface is ``/sys/kernel/platform_profile/``, containing
+``choices`` and ``profile`` attributes. These attributes are present while
+at least one provider is registered. Per-provider interfaces are available
+under ``/sys/class/platform-profile/``.
+
+On ACPI systems, ``/sys/firmware/acpi/platform_profile_choices`` and
+``/sys/firmware/acpi/platform_profile`` remain available as compatibility
+interfaces. They operate on the same providers as the system-wide interface,
+and changes are notified through both interfaces.
+
 Note that this API is only for selecting the platform profile, it is
 NOT a goal of this API to allow monitoring the resulting performance
 characteristics. Monitoring performance is best done with device/vendor
@@ -52,13 +69,14 @@ Multiple driver support
 =======================
 When multiple drivers on a system advertise a platform profile handler, the
 platform profile handler core will only advertise the profiles that are
-common between all drivers to the ``/sys/firmware/acpi`` interfaces.
+common between all drivers to the system-wide interface and its ACPI
+compatibility interface.
 
 This is to ensure there is no ambiguity on what the profile names mean when
 all handlers don't support a profile.
 
-Individual drivers will register a 'platform_profile' class device that has
-similar semantics as the ``/sys/firmware/acpi/platform_profile`` interface.
+Individual drivers register a ``platform-profile`` class device with
+``name``, ``choices`` and ``profile`` attributes.
 
 To discover which driver is associated with a platform profile handler the
 user can read the ``name`` attribute of the class device.
@@ -74,7 +92,10 @@ same system. If the selected profile by individual drivers differs the
 platform profile handler core will display the profile 'custom' to indicate
 that the profiles are not the same.
 
-While the ``platform_profile`` attribute has the value ``custom``, writing a
-common profile from ``platform_profile_choices`` to the platform_profile
-attribute of the platform profile handler core will set the profile for all
-drivers.
+While the system-wide ``profile`` attribute has the value ``custom``, writing
+a common profile from ``choices`` to it will set the profile for all drivers.
+``custom`` cannot be written to the system-wide interface.
+
+Profile changes are applied to providers sequentially. If a provider returns
+an error, providers updated earlier are not rolled back. Userspace can read
+the per-provider interfaces to determine their resulting state.
diff --git a/MAINTAINERS b/MAINTAINERS
index 8014b9f8253e..778275ff20b6 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -285,10 +285,15 @@ B:	https://bugzilla.kernel.org
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm
 F:	Documentation/ABI/testing/configfs-acpi
 F:	Documentation/ABI/testing/sysfs-bus-acpi
+F:	Documentation/ABI/testing/sysfs-class-platform-profile
+F:	Documentation/ABI/testing/sysfs-kernel-platform_profile
+F:	Documentation/ABI/testing/sysfs-platform_profile
 F:	Documentation/firmware-guide/acpi/
+F:	Documentation/userspace-api/sysfs-platform_profile.rst
 F:	arch/x86/kernel/acpi/
 F:	arch/x86/pci/acpi.c
 F:	drivers/acpi/
+F:	drivers/platform/profile/
 F:	drivers/pci/*/*acpi*
 F:	drivers/pci/*acpi*
 F:	drivers/pnp/pnpacpi/
@@ -296,6 +301,7 @@ F:	include/acpi/
 F:	include/linux/acpi.h
 F:	include/linux/fwnode.h
 F:	include/linux/fw_table.h
+F:	include/linux/platform_profile.h
 F:	lib/fw_table.c
 F:	rust/helpers/acpi.c
 F:	rust/kernel/acpi.rs
diff --git a/include/linux/platform_profile.h b/include/linux/platform_profile.h
index 855b28340e95..f23f9827eac6 100644
--- a/include/linux/platform_profile.h
+++ b/include/linux/platform_profile.h
@@ -2,6 +2,9 @@
 /*
  * Platform profile sysfs interface
  *
+ * Providers may use any firmware interface or implement profiles in software.
+ * The parent device does not need an ACPI companion or a firmware node.
+ *
  * See Documentation/userspace-api/sysfs-platform_profile.rst for more
  * information.
  */
-- 
2.43.0