Prepares the kernel for the Power State Change Reason (PSCR) recorder,
which will store shutdown and reboot reasons in persistent storage.

Instead of using string-based reason descriptions, which are often too
large to fit within limited storage spaces (e.g., RTC clocks with only 8
bits of battery-backed storage), we introduce `enum psc_reason`. This
enumerates predefined reasons for power state changes, making it
efficient to store and retrieve shutdown causes.

Key changes:
- Introduced `enum psc_reason`, defining structured reasons for power state
  changes.
- Replaced string-based shutdown reasons with `psc_reason` identifiers.
- Implemented `get_psc_reason()` and `set_psc_reason()` for tracking the
  last shutdown cause.
- Added `psc_reason_to_str()` to map enum values to human-readable strings.
- Updated `hw_protection_trigger()` to use `psc_reason` instead of string
  parameters.
- Updated all consumers of `hw_protection_trigger()` to pass an appropriate
  `psc_reason` value instead of a string.
- All structured logs now go through a single `pr_emerg()` in
  `__hw_protection_trigger()`, providing consistent output:
    HARDWARE PROTECTION <action>: <reason-code> (<reason-string>)

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Matti Vaittinen <mazziesaccount@gmail.com>
Acked-by: Mark Brown <broonie@kernel.org>
Acked-by: Tzung-Bi Shih <tzungbi@kernel.org>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
---
changes v12:
- drop Tested-by: Faruque Ansari and Francesco Valla; the end-to-end
  recording flow they tested has been reworked (multi-provider) and the
  recorder driver is no longer part of the series - re-testing is welcome
changes v10
- regulator_handle_critical: set pscr = PSCR_UNKNOWN for default case
- add Acked-by: Daniel Lezcano ..
changes v9:
- Remove redundant pr_crit() messages before hw_protection_trigger()
- Replace psc_reason_to_str() switch with static const string array
- Mark psc_last_reason as static
changes v8:
- add Acked/Reviewed-by.
changes v6:
- added in this version
(cherry picked from commit 29591d88486c392e2264de73c4e90106f181b33c)
---
 drivers/platform/chrome/cros_ec_lpc.c |   2 +-
 drivers/regulator/core.c              |  16 ++--
 drivers/regulator/irq_helpers.c       |   9 ++-
 drivers/thermal/thermal_core.c        |   3 +-
 include/linux/reboot.h                |  78 +++++++++++++++++-
 kernel/reboot.c                       | 112 +++++++++++++++++++++++++-
 6 files changed, 198 insertions(+), 22 deletions(-)

diff --git a/drivers/platform/chrome/cros_ec_lpc.c b/drivers/platform/chrome/cros_ec_lpc.c
index 78cfff80cdea..00e98d12ddbc 100644
--- a/drivers/platform/chrome/cros_ec_lpc.c
+++ b/drivers/platform/chrome/cros_ec_lpc.c
@@ -455,7 +455,7 @@ static void cros_ec_lpc_acpi_notify(acpi_handle device, u32 value, void *data)
 		blocking_notifier_call_chain(&ec_dev->panic_notifier, 0, ec_dev);
 		kobject_uevent_env(&ec_dev->dev->kobj, KOBJ_CHANGE, (char **)env);
 		/* Begin orderly shutdown. EC will force reset after a short period. */
-		__hw_protection_trigger("CrOS EC Panic", -1, HWPROT_ACT_SHUTDOWN);
+		__hw_protection_trigger(PSCR_EC_PANIC, -1, HWPROT_ACT_SHUTDOWN);
 		/* Do not query for other events after a panic is reported */
 		return;
 	}
diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index dc5d67767336..2075cf838bd4 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -5532,26 +5532,26 @@ EXPORT_SYMBOL_GPL(regulator_bulk_free);
 static void regulator_handle_critical(struct regulator_dev *rdev,
 				      unsigned long event)
 {
-	const char *reason = NULL;
+	enum psc_reason pscr;
 
 	if (!rdev->constraints->system_critical)
 		return;
 
 	switch (event) {
 	case REGULATOR_EVENT_UNDER_VOLTAGE:
-		reason = "System critical regulator: voltage drop detected";
+		pscr = PSCR_UNDER_VOLTAGE;
 		break;
 	case REGULATOR_EVENT_OVER_CURRENT:
-		reason = "System critical regulator: over-current detected";
+		pscr = PSCR_OVER_CURRENT;
 		break;
 	case REGULATOR_EVENT_FAIL:
-		reason = "System critical regulator: unknown error";
+		pscr = PSCR_REGULATOR_FAILURE;
+		break;
+	default:
+		pscr = PSCR_UNKNOWN;
 	}
 
-	if (!reason)
-		return;
-
-	hw_protection_trigger(reason,
+	hw_protection_trigger(pscr,
 			      rdev->constraints->uv_less_critical_window_ms);
 }
 
diff --git a/drivers/regulator/irq_helpers.c b/drivers/regulator/irq_helpers.c
index 5b3cfac28667..712e0ce840e7 100644
--- a/drivers/regulator/irq_helpers.c
+++ b/drivers/regulator/irq_helpers.c
@@ -64,15 +64,16 @@ static void regulator_notifier_isr_work(struct work_struct *work)
 reread:
 	if (d->fatal_cnt && h->retry_cnt > d->fatal_cnt) {
 		if (!d->die)
-			return hw_protection_trigger("Regulator HW failure? - no IC recovery",
+			return hw_protection_trigger(PSCR_REGULATOR_FAILURE,
 						     REGULATOR_FORCED_SAFETY_SHUTDOWN_WAIT_MS);
+
 		ret = d->die(rid);
 		/*
 		 * If the 'last resort' IC recovery failed we will have
 		 * nothing else left to do...
 		 */
 		if (ret)
-			return hw_protection_trigger("Regulator HW failure. IC recovery failed",
+			return hw_protection_trigger(PSCR_REGULATOR_FAILURE,
 						     REGULATOR_FORCED_SAFETY_SHUTDOWN_WAIT_MS);
 
 		/*
@@ -263,13 +264,13 @@ static irqreturn_t regulator_notifier_isr(int irq, void *data)
 	if (d->fatal_cnt && h->retry_cnt > d->fatal_cnt) {
 		/* If we have no recovery, just try shut down straight away */
 		if (!d->die) {
-			hw_protection_trigger("Regulator failure. Retry count exceeded",
+			hw_protection_trigger(PSCR_REGULATOR_FAILURE,
 					      REGULATOR_FORCED_SAFETY_SHUTDOWN_WAIT_MS);
 		} else {
 			ret = d->die(rid);
 			/* If die() failed shut down as a last attempt to save the HW */
 			if (ret)
-				hw_protection_trigger("Regulator failure. Recovery failed",
+				hw_protection_trigger(PSCR_REGULATOR_FAILURE,
 						      REGULATOR_FORCED_SAFETY_SHUTDOWN_WAIT_MS);
 		}
 	}
diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
index 28a20d4b475c..df8fa11f78dc 100644
--- a/drivers/thermal/thermal_core.c
+++ b/drivers/thermal/thermal_core.c
@@ -319,11 +319,10 @@ static void thermal_zone_device_halt(struct thermal_zone_device *tz,
 	 * Its a must for forced_emergency_poweroff_work to be scheduled.
 	 */
 	int poweroff_delay_ms = CONFIG_THERMAL_EMERGENCY_POWEROFF_DELAY_MS;
-	const char *msg = "Temperature too high";
 
 	dev_emerg(&tz->device, "%s: critical temperature reached\n", tz->type);
 
-	__hw_protection_trigger(msg, poweroff_delay_ms, action);
+	__hw_protection_trigger(PSCR_OVER_TEMPERATURE, poweroff_delay_ms, action);
 }
 
 void thermal_zone_device_critical(struct thermal_zone_device *tz)
diff --git a/include/linux/reboot.h b/include/linux/reboot.h
index aa08c3bbbf59..08a7549bbc40 100644
--- a/include/linux/reboot.h
+++ b/include/linux/reboot.h
@@ -178,6 +178,73 @@ void ctrl_alt_del(void);
 extern void orderly_poweroff(bool force);
 extern void orderly_reboot(void);
 
+
+/**
+ * enum psc_reason - Enumerates reasons for power state changes.
+ *
+ * This enum defines various reasons why a system might transition into a
+ * shutdown, reboot, or kexec state. While originally intended for hardware
+ * protection events, `psc_reason` can be extended to track other system
+ * transitions, such as controlled reboots triggered by software or
+ * maintenance operations.
+ *
+ * The values in this enumeration provide structured and standardized
+ * identifiers that replace free-form string descriptions. They are designed
+ * to be stored efficiently, making them suitable for use in environments
+ * with limited storage, such as battery-backed RTC registers, non-volatile
+ * memory, or bootloader communication mechanisms.
+ *
+ * Importantly, the order of these values **must remain stable**, as
+ * bootloaders, user-space tools, or post-mortem investigation utilities
+ * may rely on their numerical representation for consistent behavior.
+ *
+ * @PSCR_UNKNOWN: Unknown or unspecified reason for the power state change.
+ *	This value serves as a default when no explicit cause is recorded.
+ *
+ * @PSCR_UNDER_VOLTAGE: Shutdown or reboot triggered due to supply voltage
+ *      dropping below a safe threshold. This helps prevent instability or
+ *      corruption caused by insufficient power.
+ *
+ * @PSCR_OVER_CURRENT: System shutdown or reboot due to excessive current draw,
+ *      which may indicate a short circuit, an overloaded power rail, or other
+ *      hardware faults requiring immediate action.
+ *
+ * @PSCR_REGULATOR_FAILURE: A critical failure in a voltage regulator, causing
+ *      improper power delivery. This may be due to internal component failure,
+ *      transient conditions, or external load issues requiring mitigation.
+ *
+ * @PSCR_OVER_TEMPERATURE: System shutdown or reboot due to excessive thermal
+ *	conditions. This attempts to prevent hardware damage when temperature
+ *	sensors detect unsafe levels, often impacting CPUs, GPUs, or power
+ *	components.
+ *
+ * @PSCR_EC_PANIC: Shutdown or reboot triggered by an Embedded Controller (EC)
+ *	panic. The EC is a microcontroller responsible for low-level system
+ *	management, including power sequencing, thermal control, and battery
+ *	management. An EC panic may indicate critical firmware issues, power
+ *	management errors, or an unrecoverable hardware fault requiring
+ *	immediate response.
+ *
+ * @PSCR_REASON_COUNT: Number of defined power state change reasons. This
+ *	value is useful for range checking and potential future extensions
+ *	while maintaining compatibility.
+ */
+enum psc_reason {
+	PSCR_UNKNOWN,
+	PSCR_UNDER_VOLTAGE,
+	PSCR_OVER_CURRENT,
+	PSCR_REGULATOR_FAILURE,
+	PSCR_OVER_TEMPERATURE,
+	PSCR_EC_PANIC,
+
+	/* Number of reasons */
+	PSCR_REASON_COUNT,
+};
+
+#define PSCR_MAX_REASON	(PSCR_REASON_COUNT - 1)
+
+const char *psc_reason_to_str(enum psc_reason reason);
+
 /**
  * enum hw_protection_action - Hardware protection action
  *
@@ -191,13 +258,13 @@ extern void orderly_reboot(void);
  */
 enum hw_protection_action { HWPROT_ACT_DEFAULT, HWPROT_ACT_SHUTDOWN, HWPROT_ACT_REBOOT };
 
-void __hw_protection_trigger(const char *reason, int ms_until_forced,
+void __hw_protection_trigger(enum psc_reason reason, int ms_until_forced,
 			     enum hw_protection_action action);
 
 /**
  * hw_protection_trigger - Trigger default emergency system hardware protection action
  *
- * @reason:		Reason of emergency shutdown or reboot to be printed.
+ * @reason:		Reason of emergency shutdown or reboot.
  * @ms_until_forced:	Time to wait for orderly shutdown or reboot before
  *			triggering it. Negative value disables the forced
  *			shutdown or reboot.
@@ -206,11 +273,16 @@ void __hw_protection_trigger(const char *reason, int ms_until_forced,
  * hardware from further damage. The exact action taken is controllable at
  * runtime and defaults to shutdown.
  */
-static inline void hw_protection_trigger(const char *reason, int ms_until_forced)
+static inline void hw_protection_trigger(enum psc_reason reason,
+					 int ms_until_forced)
 {
 	__hw_protection_trigger(reason, ms_until_forced, HWPROT_ACT_DEFAULT);
 }
 
+enum psc_reason get_psc_reason(void);
+enum psc_reason get_psc_first_reason(void);
+void set_psc_reason(enum psc_reason reason);
+
 /*
  * Emergency restart, callable from an interrupt handler.
  */
diff --git a/kernel/reboot.c b/kernel/reboot.c
index 695c33e75efd..29c68441fa53 100644
--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -13,6 +13,7 @@
 #include <linux/kexec.h>
 #include <linux/kmod.h>
 #include <linux/kmsg_dump.h>
+#include <linux/power/power_on_reason.h>
 #include <linux/reboot.h>
 #include <linux/suspend.h>
 #include <linux/syscalls.h>
@@ -49,6 +50,8 @@ int reboot_default = 1;
 int reboot_cpu;
 enum reboot_type reboot_type = BOOT_ACPI;
 int reboot_force;
+static enum psc_reason psc_last_reason = PSCR_UNKNOWN;
+static enum psc_reason psc_first_reason = PSCR_UNKNOWN;
 
 struct sys_off_handler {
 	struct notifier_block nb;
@@ -1010,10 +1013,108 @@ static void hw_failure_emergency_schedule(enum hw_protection_action action,
 			      msecs_to_jiffies(action_delay_ms));
 }
 
+/**
+ * get_psc_reason - Retrieve the last recorded power state change reason.
+ *
+ * This function returns the most recent power state change reason stored
+ * in `psc_last_reason`. The value is set using `set_psc_reason()` when a
+ * shutdown, reboot, or kexec event occurs.
+ *
+ * The reason can be used for system diagnostics, post-mortem analysis, or
+ * debugging unexpected power state changes. Bootloaders or user-space tools
+ * may retrieve this value to determine why the system last transitioned to
+ * a new power state.
+ *
+ * Return: A value from `enum psc_reason`, indicating the last known power
+ * state change reason.
+ */
+enum psc_reason get_psc_reason(void)
+{
+	return READ_ONCE(psc_last_reason);
+}
+EXPORT_SYMBOL_GPL(get_psc_reason);
+
+/**
+ * get_psc_first_reason - Retrieve the first power state change reason.
+ *
+ * Returns the first meaningful (non-PSCR_UNKNOWN) reason recorded during this
+ * boot, i.e. the root cause, as opposed to get_psc_reason() which returns the
+ * most recent one. A later event (a watchdog pretimeout, a kernel panic, ...)
+ * updates the last reason but leaves this one untouched, so a recorder using
+ * the "first" record policy can preserve the original cause.
+ *
+ * Return: A value from `enum psc_reason`.
+ */
+enum psc_reason get_psc_first_reason(void)
+{
+	return READ_ONCE(psc_first_reason);
+}
+EXPORT_SYMBOL_GPL(get_psc_first_reason);
+
+/**
+ * set_psc_reason - Set the reason for the last power state change.
+ *
+ * @reason: A value from `enum psc_reason` indicating the cause of the power
+ *          state change.
+ *
+ * This function records the reason for a shutdown, reboot, or kexec event
+ * by storing it in `psc_last_reason`. It ensures that the value remains
+ * consistent within the running system, allowing retrieval via
+ * `get_psc_reason()` for diagnostics, logging, or post-mortem analysis.
+ *
+ * Persistence Consideration:
+ * - This function **does not persist** the recorded reason across power cycles.
+ * - After a system reset or complete power loss, the recorded reason is lost.
+ * - To store power state change reasons persistently, additional tools such as
+ *   the Power State Change Reason Recorder (PSCRR) framework should be used.
+ */
+void set_psc_reason(enum psc_reason reason)
+{
+	WRITE_ONCE(psc_last_reason, reason);
+
+	/*
+	 * Latch the first meaningful reason of this boot as the root cause, so
+	 * that a later event overwriting the last reason does not hide it from
+	 * a recorder using the "first" record policy.
+	 */
+	if (reason != PSCR_UNKNOWN &&
+	    READ_ONCE(psc_first_reason) == PSCR_UNKNOWN)
+		WRITE_ONCE(psc_first_reason, reason);
+}
+EXPORT_SYMBOL_GPL(set_psc_reason);
+
+static const char * const pscr_reason_strs[] = {
+	[PSCR_UNKNOWN]            = POWER_ON_REASON_UNKNOWN,
+	[PSCR_UNDER_VOLTAGE]      = POWER_ON_REASON_BROWN_OUT,
+	[PSCR_OVER_CURRENT]       = POWER_ON_REASON_OVER_CURRENT,
+	[PSCR_REGULATOR_FAILURE]  = POWER_ON_REASON_REGULATOR_FAILURE,
+	[PSCR_OVER_TEMPERATURE]   = POWER_ON_REASON_OVER_TEMPERATURE,
+	[PSCR_EC_PANIC]           = POWER_ON_REASON_EC_PANIC,
+};
+
+/**
+ * psc_reason_to_str - Converts a power state change reason enum to a string.
+ * @reason: The `psc_reason` enum value to be converted.
+ *
+ * This function provides a human-readable string representation of the power
+ * state change reason, making it easier to interpret logs and debug messages.
+ *
+ * Return:
+ * - A string corresponding to the given `psc_reason` value.
+ * - `"Invalid"` if the value is not recognized.
+ */
+const char *psc_reason_to_str(enum psc_reason reason)
+{
+	if (reason < 0 || reason >= PSCR_REASON_COUNT)
+		return "Invalid";
+	return pscr_reason_strs[reason];
+}
+EXPORT_SYMBOL_GPL(psc_reason_to_str);
+
 /**
  * __hw_protection_trigger - Trigger an emergency system shutdown or reboot
  *
- * @reason:		Reason of emergency shutdown or reboot to be printed.
+ * @reason:		Reason of emergency shutdown or reboot.
  * @ms_until_forced:	Time to wait for orderly shutdown or reboot before
  *			triggering it. Negative value disables the forced
  *			shutdown or reboot.
@@ -1025,7 +1126,7 @@ static void hw_failure_emergency_schedule(enum hw_protection_action action,
  * pending even if the previous request has given a large timeout for forced
  * shutdown/reboot.
  */
-void __hw_protection_trigger(const char *reason, int ms_until_forced,
+void __hw_protection_trigger(enum psc_reason reason, int ms_until_forced,
 			     enum hw_protection_action action)
 {
 	static atomic_t allow_proceed = ATOMIC_INIT(1);
@@ -1033,8 +1134,11 @@ void __hw_protection_trigger(const char *reason, int ms_until_forced,
 	if (action == HWPROT_ACT_DEFAULT)
 		action = hw_protection_action;
 
-	pr_emerg("HARDWARE PROTECTION %s (%s)\n",
-		 hw_protection_action_str(action), reason);
+	set_psc_reason(reason);
+
+	pr_emerg("HARDWARE PROTECTION %s: %i (%s)\n",
+		 hw_protection_action_str(action), reason,
+		 psc_reason_to_str(reason));
 
 	/* Shutdown should be initiated only once. */
 	if (!atomic_dec_and_test(&allow_proceed))
-- 
2.47.3