regulator: Introduce handling for system-critical under-voltage events

Handle under-voltage events for crucial regulators to maintain system
stability and avoid issues during power drops.
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://lore.kernel.org/r/20231026144824.4065145-3-o.rempel@pengutronix.deSigned-off-by: Mark Brown <broonie@kernel.org>

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>
@@ -5061,6 +5062,41 @@ 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,
+			       REGULATOR_DEF_UV_LESS_CRITICAL_WINDOW_MS);
+}
+
 /**
  * regulator_notifier_call_chain - call regulator event notifier
  * @rdev: regulator source
@@ -5073,6 +5109,8 @@ 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;

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.
@@ -214,6 +223,7 @@ 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 */