regulator: Implement uv_survival_time for handling under-voltage events

Add 'uv_survival_time' field to regulation_constraints for specifying
survival time post critical under-voltage event. Update the regulator
notifier call chain and Device Tree property parsing to use this new
field, allowing a configurable timeout before emergency shutdown.
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://lore.kernel.org/r/20231026144824.4065145-6-o.rempel@pengutronix.deSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/core.c

@@ -5094,7 +5094,7 @@ static void regulator_handle_critical(struct regulator_dev *rdev,
 		return;
 
 	hw_protection_shutdown(reason,
-			       REGULATOR_DEF_UV_LESS_CRITICAL_WINDOW_MS);
+			       rdev->constraints->uv_less_critical_window_ms);
 }
 
 /**

drivers/regulator/of_regulator.c

@@ -175,6 +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

@@ -162,6 +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 {
 
@@ -213,6 +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;