[PATCH v2 4/5] platform profile: Document firmware-independent profile selection

[Daniel Lezcano]

Describe the existing per-provider class devices as the firmware-neutral
userspace interface. Explain that providers can use any firmware transport
or implement profiles in software, without an ACPI companion or firmware
node on their parent device.

Retain the ACPI paths as compatibility interfaces for aggregate selection.
Clarify that non-ACPI userspace selects individual providers and document
the sequential application of aggregate writes and their partial-failure
behavior. No new userspace ABI is introduced.

Correct the per-provider choices 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 +-
 .../userspace-api/sysfs-platform_profile.rst  | 46 ++++++++++++++-----
 MAINTAINERS                                   |  5 ++
 include/linux/platform_profile.h              |  3 ++
 4 files changed, 43 insertions(+), 13 deletions(-)

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/userspace-api/sysfs-platform_profile.rst b/Documentation/userspace-api/sysfs-platform_profile.rst
index 6613e188242a..a85ede3fb8e5 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 firmware-independent userspace interface is available under
+``/sys/class/platform-profile/platform-profile-X/``, with ``name``,
+``choices`` and ``profile`` attributes for each registered provider.
+
+On ACPI systems, ``/sys/firmware/acpi/platform_profile_choices`` and
+``/sys/firmware/acpi/platform_profile`` remain available as compatibility
+interfaces for aggregate profile selection across registered providers.
+On non-ACPI systems, userspace selects profiles through the individual
+provider class devices.
+
 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 ``/sys/firmware/acpi`` interfaces, when
+ACPI is active.
 
 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.
@@ -71,10 +89,14 @@ by writing to the ``profile`` attribute of the driver's class device.
 
 This will allow users to set different profiles for different drivers on the
 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.
+ACPI aggregate interface will display the profile 'custom' to indicate that
+the profiles are not the same.
+
+While the ACPI ``platform_profile`` attribute has the value ``custom``,
+writing a common profile from ``platform_profile_choices`` to it will set
+the profile for all drivers. ``custom`` cannot be written to this aggregate
+interface.
 
-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.
+Aggregate 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..929e1e095f17 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -285,10 +285,14 @@ 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-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 +300,7 @@ 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