[PATCH v2 5/5] platform profile: Make legacy ACPI aggregate interface optional

[Daniel Lezcano <daniel.lezcano@oss.qualcomm.com>]

The aggregate attributes under /sys/firmware/acpi/ are retained
for backwards compatibility. Firmware-independent userspace can already
discover providers through /sys/class/platform-profile/ and control each
provider using its choices and profile attributes.

Add PLATFORM_PROFILE_LEGACY, a boolean depending on PLATFORM_PROFILE and
ACPI, to control the legacy aggregate sysfs interface. Default it to y so
existing userspace continues to work when updating its configuration.

Compile the ACPI adapter and legacy sysfs callbacks only when the option
is enabled. Keep common aggregation helpers in the core because kernel
hotkey users still need platform_profile_cycle(). Class devices and their
notifications remain available regardless of the legacy option.

Document the compatibility option and recommend individual class devices
for new userspace. No daemon changes are included in this kernel series.
Move the legacy ABI documentation to obsolete/, retain its original
creation dates and attribute descriptions, identify the replacement class
attributes, and update its MAINTAINERS entry.

Mark the legacy ABI deprecated and document removal after the 2028 LTS
kernel, conditional on userspace migration. Keep the enabled default
until class-device support has been released and deployed in userspace.
Emit one shared pr_notice_once() when either legacy attribute is read or
the profile is written, identifying actual legacy use rather than warning
merely because the compatibility code was loaded.

Validate ARM64 without ACPI and x86 module builds with the option enabled
and disabled. With ACPI active and the option disabled, QEMU tests confirm
that the legacy attributes are absent while class controls, notifications,
kernel cycling and concurrent registration/removal continue to work.

Assisted-by: OpenCode:gpt-6.1-sol
Signed-off-by: Daniel Lezcano <daniel.lezcano@oss.qualcomm.com>
---
 .../{testing => obsolete}/sysfs-platform_profile   | 12 ++++
 .../userspace-api/sysfs-platform_profile.rst       | 17 +++--
 MAINTAINERS                                        |  2 +-
 drivers/platform/Kconfig                           | 23 ++++++-
 drivers/platform/profile/Makefile                  |  2 +-
 drivers/platform/profile/core.c                    | 72 ++++++++++++++++++----
 drivers/platform/profile/profile.h                 |  2 +-
 7 files changed, 109 insertions(+), 21 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-platform_profile b/Documentation/ABI/obsolete/sysfs-platform_profile
similarity index 70%
rename from Documentation/ABI/testing/sysfs-platform_profile
rename to Documentation/ABI/obsolete/sysfs-platform_profile
index 125324ab53a9..c001c8641a3a 100644
--- a/Documentation/ABI/testing/sysfs-platform_profile
+++ b/Documentation/ABI/obsolete/sysfs-platform_profile
@@ -2,6 +2,12 @@ What:		/sys/firmware/acpi/platform_profile_choices
 Date:		October 2020
 Contact:	Hans de Goede <hdegoede@redhat.com>
 Description:	This file contains a space-separated list of profiles supported for this device.
+		Available with CONFIG_PLATFORM_PROFILE_LEGACY on active ACPI
+		systems for backwards compatibility. New userspace should use
+		/sys/class/platform-profile/platform-profile-X/choices instead.
+		This interface is deprecated, with removal intended after the
+		2028 LTS kernel once userspace migration is complete. Accessing
+		either legacy attribute emits a one-time deprecation notice.
 
 		Drivers must use the following standard profile-names:
 
@@ -27,6 +33,12 @@ 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.
 
+		This legacy interface requires CONFIG_PLATFORM_PROFILE_LEGACY.
+		Individual class devices remain available without that option.
+		Use /sys/class/platform-profile/platform-profile-X/profile
+		instead. This interface is deprecated, with removal intended
+		after the 2028 LTS kernel once userspace migration is complete.
+
 		This file can be monitored for changes by polling for POLLPRI,
 		POLLPRI will be signalled on any changes, independent of those
 		changes coming from a userspace write; or coming from another
diff --git a/Documentation/userspace-api/sysfs-platform_profile.rst b/Documentation/userspace-api/sysfs-platform_profile.rst
index a85ede3fb8e5..a3fc1ee20832 100644
--- a/Documentation/userspace-api/sysfs-platform_profile.rst
+++ b/Documentation/userspace-api/sysfs-platform_profile.rst
@@ -26,11 +26,20 @@ 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
+On ACPI systems with ``CONFIG_PLATFORM_PROFILE_LEGACY`` enabled,
+``/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.
+New userspace should select profiles through the individual provider class
+devices. These remain available when the legacy interface is disabled and
+on non-ACPI systems. Kernel profile cycling also remains available without
+the legacy interface.
+
+The legacy aggregate interface is deprecated. Removal is intended after the
+2028 LTS kernel, once userspace has migrated to released software using the
+class devices. Compatibility remains enabled by default during the migration;
+the date alone does not trigger removal. Accessing either legacy attribute
+emits a one-time kernel notice directing userspace to the class interface.
 
 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
@@ -70,7 +79,7 @@ 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, when
-ACPI is active.
+ACPI is active and ``CONFIG_PLATFORM_PROFILE_LEGACY`` is enabled.
 
 This is to ensure there is no ambiguity on what the profile names mean when
 all handlers don't support a profile.
diff --git a/MAINTAINERS b/MAINTAINERS
index 929e1e095f17..47b7724f20ea 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -283,10 +283,10 @@ S:	Supported
 Q:	https://patchwork.kernel.org/project/linux-acpi/list/
 B:	https://bugzilla.kernel.org
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm
+F:	Documentation/ABI/obsolete/sysfs-platform_profile
 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/
diff --git a/drivers/platform/Kconfig b/drivers/platform/Kconfig
index 395b75f2edf0..7270f24a3b6e 100644
--- a/drivers/platform/Kconfig
+++ b/drivers/platform/Kconfig
@@ -9,12 +9,31 @@ config PLATFORM_PROFILE
 
 	  The core exposes per-provider controls under /sys/class/platform-profile/.
 	  A provider driver must register before profile attributes become
-	  available. ACPI is not required; on ACPI systems the legacy system-wide
-	  interface under /sys/firmware/acpi/ is also provided.
+	  available. ACPI is not required. The legacy system-wide interface under
+	  /sys/firmware/acpi/ can be enabled separately for existing userspace.
 
 	  To compile this as a module, choose M here: the module will be called
 	  platform_profile.
 
+config PLATFORM_PROFILE_LEGACY
+	bool "Legacy ACPI platform profile sysfs interface (DEPRECATED)"
+	depends on PLATFORM_PROFILE && ACPI
+	default y
+	help
+	  Expose platform_profile and platform_profile_choices under
+	  /sys/firmware/acpi/ for compatibility with existing userspace. These
+	  attributes aggregate the profiles of all registered providers.
+
+	  This interface is deprecated and is intended for removal after the
+	  2028 LTS kernel, once userspace has migrated to the class interface.
+	  It remains enabled by default until replacement userspace releases
+	  are available and have had time to reach users.
+
+	  New userspace should use the individual devices under
+	  /sys/class/platform-profile/ instead. Disabling this option removes
+	  the legacy sysfs interface but retains class devices and kernel
+	  profile cycling. If unsure, say Y to preserve compatibility.
+
 source "drivers/platform/mips/Kconfig"
 
 source "drivers/platform/loongarch/Kconfig"
diff --git a/drivers/platform/profile/Makefile b/drivers/platform/profile/Makefile
index ae95ba09383c..787fc9bc961a 100644
--- a/drivers/platform/profile/Makefile
+++ b/drivers/platform/profile/Makefile
@@ -2,4 +2,4 @@
 obj-$(CONFIG_PLATFORM_PROFILE) += platform_profile.o
 
 platform_profile-y := core.o
-platform_profile-$(CONFIG_ACPI) += acpi.o
+platform_profile-$(CONFIG_PLATFORM_PROFILE_LEGACY) += acpi.o
diff --git a/drivers/platform/profile/core.c b/drivers/platform/profile/core.c
index 320a5a964fea..1bffca947157 100644
--- a/drivers/platform/profile/core.c
+++ b/drivers/platform/profile/core.c
@@ -25,12 +25,16 @@ static DEFINE_MUTEX(profile_lock);
 /* Serialize registration and sysfs updates without blocking sysfs callbacks. */
 static DEFINE_MUTEX(profile_registration_lock);
 static LIST_HEAD(profile_handlers);
+#ifdef CONFIG_PLATFORM_PROFILE_LEGACY
 static struct kobject *compat_kobj;
+#endif
 
 static void profile_notify(void)
 {
+#ifdef CONFIG_PLATFORM_PROFILE_LEGACY
 	if (compat_kobj)
 		sysfs_notify(compat_kobj, NULL, "platform_profile");
+#endif
 }
 
 static int profile_update(void);
@@ -304,6 +308,12 @@ static int _aggregate_choices(struct device *dev, void *arg)
 	return 0;
 }
 
+#ifdef CONFIG_PLATFORM_PROFILE_LEGACY
+static void profile_legacy_notice(void)
+{
+	pr_notice_once("The ACPI platform_profile sysfs interface is deprecated and planned for removal after the 2028 LTS kernel once userspace has migrated; use /sys/class/platform-profile/ instead\n");
+}
+
 /**
  * _remove_hidden_choices - Remove hidden choices from aggregate data
  * @dev: The device
@@ -342,6 +352,8 @@ static ssize_t platform_profile_choices_show(struct kobject *kobj,
 	};
 	int err;
 
+	profile_legacy_notice();
+
 	scoped_cond_guard(mutex_intr, return -ERESTARTSYS, &profile_lock) {
 		err = profile_walk_handlers(&data, _aggregate_choices);
 		if (err)
@@ -359,6 +371,7 @@ static ssize_t platform_profile_choices_show(struct kobject *kobj,
 
 	return _commmon_choices_show(data.aggregate, buf);
 }
+#endif
 
 /**
  * _aggregate_profiles - Aggregate the profiles across providers
@@ -403,6 +416,7 @@ static int _store_and_notify(struct device *dev, void *data)
 	return _notify_class_profile(dev, NULL);
 }
 
+#ifdef CONFIG_PLATFORM_PROFILE_LEGACY
 /**
  * platform_profile_show - Show the current aggregate profile
  * @kobj: The kobject
@@ -418,6 +432,8 @@ static ssize_t platform_profile_show(struct kobject *kobj,
 	enum platform_profile_option profile = PLATFORM_PROFILE_LAST;
 	int err;
 
+	profile_legacy_notice();
+
 	scoped_cond_guard(mutex_intr, return -ERESTARTSYS, &profile_lock) {
 		err = profile_walk_handlers(&profile, _aggregate_profiles);
 		if (err)
@@ -451,6 +467,8 @@ static ssize_t platform_profile_store(struct kobject *kobj,
 	int ret;
 	int i;
 
+	profile_legacy_notice();
+
 	/* Scan for a matching profile */
 	i = sysfs_match_string(profile_names, buf);
 	if (i < 0 || i == PLATFORM_PROFILE_CUSTOM)
@@ -502,6 +520,44 @@ static int profile_update(void)
 	return 0;
 }
 
+static int profile_compat_init(void)
+{
+	int err;
+
+	compat_kobj = platform_profile_compat_kobj();
+	if (!compat_kobj)
+		return 0;
+
+	err = sysfs_create_group(compat_kobj, &platform_profile_group);
+	if (err)
+		kobject_put(compat_kobj);
+
+	return err;
+}
+
+static void profile_compat_exit(void)
+{
+	if (compat_kobj) {
+		sysfs_remove_group(compat_kobj, &platform_profile_group);
+		kobject_put(compat_kobj);
+	}
+}
+#else
+static int profile_update(void)
+{
+	return 0;
+}
+
+static int profile_compat_init(void)
+{
+	return 0;
+}
+
+static void profile_compat_exit(void)
+{
+}
+#endif
+
 /**
  * platform_profile_notify - Notify the provider and aggregate sysfs interfaces
  * @dev: The class device
@@ -728,24 +784,16 @@ static int __init platform_profile_init(void)
 	if (err)
 		return err;
 
-	compat_kobj = platform_profile_compat_kobj();
-	if (compat_kobj) {
-		err = sysfs_create_group(compat_kobj, &platform_profile_group);
-		if (err) {
-			kobject_put(compat_kobj);
-			class_unregister(&platform_profile_class);
-		}
-	}
+	err = profile_compat_init();
+	if (err)
+		class_unregister(&platform_profile_class);
 
 	return err;
 }
 
 static void __exit platform_profile_exit(void)
 {
-	if (compat_kobj) {
-		sysfs_remove_group(compat_kobj, &platform_profile_group);
-		kobject_put(compat_kobj);
-	}
+	profile_compat_exit();
 	class_unregister(&platform_profile_class);
 }
 subsys_initcall_sync(platform_profile_init);
diff --git a/drivers/platform/profile/profile.h b/drivers/platform/profile/profile.h
index 910c9f7da6a0..362eb8cc4592 100644
--- a/drivers/platform/profile/profile.h
+++ b/drivers/platform/profile/profile.h
@@ -5,7 +5,7 @@
 #include <linux/kconfig.h>
 #include <linux/kobject.h>
 
-#ifdef CONFIG_ACPI
+#ifdef CONFIG_PLATFORM_PROFILE_LEGACY
 struct kobject *platform_profile_compat_kobj(void);
 #else
 static inline struct kobject *platform_profile_compat_kobj(void)