regulator: add under-voltage support (part 2)

Merge series from Oleksij Rempel <o.rempel@pengutronix.de>:

This series add under-voltage and emergency shutdown for system critical
regulators

Documentation/devicetree/bindings/regulator/fixed-regulator.yaml

@@ -105,6 +105,8 @@ properties:
     description:
       Interrupt signaling a critical under-voltage event.
 
+  system-critical-regulator: true
+
 required:
   - compatible
   - regulator-name

Documentation/devicetree/bindings/regulator/regulator.yaml

@@ -114,6 +114,11 @@ properties:
     description: Enable pull down resistor when the regulator is disabled.
     type: boolean
 
+  system-critical-regulator:
+    description: Set if the regulator is critical to system stability or
+      functionality.
+    type: boolean
+
   regulator-over-current-protection:
     description: Enable over current protection.
     type: boolean
@@ -181,6 +186,14 @@ properties:
       be enabled but limit setting can be omitted. Limit is given as microvolt
       offset from voltage set to regulator.
 
+  regulator-uv-less-critical-window-ms:
+    description: Specifies the time window (in milliseconds) following a
+      critical under-voltage event during which the system can continue to
+      operate safely while performing less critical operations. This property
+      provides a defined duration before a more severe reaction to the
+      under-voltage event is needed, allowing for certain non-urgent actions to
+      be carried out in preparation for potential power loss.
+
   regulator-temp-protection-kelvin:
     description: Set over temperature protection limit. This is a limit where
       hardware performs emergency shutdown. Zero can be passed to disable

drivers/regulator/core.c

@@ -19,6 +19,7 @@
 #include <linux/delay.h>
 #include <linux/gpio/consumer.h>
 #include <linux/of.h>
+#include <linux/reboot.h>
 #include <linux/regmap.h>
 #include <linux/regulator/of_regulator.h>
 #include <linux/regulator/consumer.h>
@@ -5065,6 +5066,41 @@ void regulator_bulk_free(int num_consumers,
 }
 EXPORT_SYMBOL_GPL(regulator_bulk_free);
 
+/**
+ * regulator_handle_critical - Handle events for system-critical regulators.
+ * @rdev: The regulator device.
+ * @event: The event being handled.
+ *
+ * This function handles critical events such as under-voltage, over-current,
+ * and unknown errors for regulators deemed system-critical. On detecting such
+ * events, it triggers a hardware protection shutdown with a defined timeout.
+ */
+static void regulator_handle_critical(struct regulator_dev *rdev,
+				      unsigned long event)
+{
+	const char *reason = NULL;
+
+	if (!rdev->constraints->system_critical)
+		return;
+
+	switch (event) {
+	case REGULATOR_EVENT_UNDER_VOLTAGE:
+		reason = "System critical regulator: voltage drop detected";
+		break;
+	case REGULATOR_EVENT_OVER_CURRENT:
+		reason = "System critical regulator: over-current detected";
+		break;
+	case REGULATOR_EVENT_FAIL:
+		reason = "System critical regulator: unknown error";
+	}
+
+	if (!reason)
+		return;
+
+	hw_protection_shutdown(reason,
+			       rdev->constraints->uv_less_critical_window_ms);
+}
+
 /**
  * regulator_notifier_call_chain - call regulator event notifier
  * @rdev: regulator source
@@ -5077,6 +5113,8 @@ EXPORT_SYMBOL_GPL(regulator_bulk_free);
 int regulator_notifier_call_chain(struct regulator_dev *rdev,
 				  unsigned long event, void *data)
 {
+	regulator_handle_critical(rdev, event);
+
 	_notifier_call_chain(rdev, event, data);
 	return NOTIFY_DONE;
 

drivers/regulator/of_regulator.c

@@ -131,6 +131,8 @@ static int of_get_regulation_constraints(struct device *dev,
 		constraints->valid_ops_mask |= REGULATOR_CHANGE_STATUS;
 
 	constraints->pull_down = of_property_read_bool(np, "regulator-pull-down");
+	constraints->system_critical = of_property_read_bool(np,
+						"system-critical-regulator");
 
 	if (of_property_read_bool(np, "regulator-allow-bypass"))
 		constraints->valid_ops_mask |= REGULATOR_CHANGE_BYPASS;
@@ -173,6 +175,13 @@ static int of_get_regulation_constraints(struct device *dev,
 	if (!ret)
 		constraints->enable_time = pval;
 
+	ret = of_property_read_u32(np, "regulator-uv-survival-time-ms", &pval);
+	if (!ret)
+		constraints->uv_less_critical_window_ms = pval;
+	else
+		constraints->uv_less_critical_window_ms =
+				REGULATOR_DEF_UV_LESS_CRITICAL_WINDOW_MS;
+
 	constraints->soft_start = of_property_read_bool(np,
 					"regulator-soft-start");
 	ret = of_property_read_u32(np, "regulator-active-discharge", &pval);

include/linux/regulator/machine.h

@@ -49,6 +49,13 @@ struct regulator;
 #define DISABLE_IN_SUSPEND	1
 #define ENABLE_IN_SUSPEND	2
 
+/*
+ * Default time window (in milliseconds) following a critical under-voltage
+ * event during which less critical actions can be safely carried out by the
+ * system.
+ */
+#define REGULATOR_DEF_UV_LESS_CRITICAL_WINDOW_MS	10
+
 /* Regulator active discharge flags */
 enum regulator_active_discharge {
 	REGULATOR_ACTIVE_DISCHARGE_DEFAULT,
@@ -127,6 +134,8 @@ struct notification_limit {
  * @ramp_disable: Disable ramp delay when initialising or when setting voltage.
  * @soft_start: Enable soft start so that voltage ramps slowly.
  * @pull_down: Enable pull down when regulator is disabled.
+ * @system_critical: Set if the regulator is critical to system stability or
+ *                   functionality.
  * @over_current_protection: Auto disable on over current event.
  *
  * @over_current_detection: Configure over current limits.
@@ -153,6 +162,13 @@ struct notification_limit {
  *		      regulator_active_discharge values are used for
  *		      initialisation.
  * @enable_time: Turn-on time of the rails (unit: microseconds)
+ * @uv_less_critical_window_ms: Specifies the time window (in milliseconds)
+ *                              following a critical under-voltage (UV) event
+ *                              during which less critical actions can be
+ *                              safely carried out by the system (for example
+ *                              logging). After this time window more critical
+ *                              actions should be done (for example prevent
+ *                              HW damage).
  */
 struct regulation_constraints {
 
@@ -204,6 +220,7 @@ struct regulation_constraints {
 	unsigned int settling_time_up;
 	unsigned int settling_time_down;
 	unsigned int enable_time;
+	unsigned int uv_less_critical_window_ms;
 
 	unsigned int active_discharge;
 
@@ -214,6 +231,7 @@ struct regulation_constraints {
 	unsigned ramp_disable:1; /* disable ramp delay */
 	unsigned soft_start:1;	/* ramp voltage slowly */
 	unsigned pull_down:1;	/* pull down resistor when regulator off */
+	unsigned system_critical:1;	/* critical to system stability */
 	unsigned over_current_protection:1; /* auto disable on over current */
 	unsigned over_current_detection:1; /* notify on over current */
 	unsigned over_voltage_detection:1; /* notify on over voltage */