drivers: regulator-fixed: extend api of driver (list/count voltages)

Allow properties 'regulator-min-microvolt' and 'regulator-max-microvolt'
for fixed regulators: Note: they should be equal.

Add simple functions for getting list of allowed and count of voltages.

Signed-off-by: Mykola Kvach <mykola_kvach@epam.com>

drivers/regulator/regulator_fixed.c

@@ -59,9 +59,33 @@ static int regulator_fixed_disable(const struct device *dev)
 	return gpio_pin_set_dt(&cfg->enable, 0);
 }
 
+static unsigned int regulator_fixed_count_voltages(const struct device *dev)
+{
+	int32_t min_uv;
+
+	return (regulator_common_get_min_voltage(dev, &min_uv) < 0) ? 0U : 1U;
+}
+
+static int regulator_fixed_list_voltage(const struct device *dev,
+					unsigned int idx,
+					int32_t *volt_uv)
+{
+	if (idx != 0) {
+		return -EINVAL;
+	}
+
+	if (regulator_common_get_min_voltage(dev, volt_uv) < 0) {
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static const struct regulator_driver_api regulator_fixed_api = {
 	.enable = regulator_fixed_enable,
 	.disable = regulator_fixed_disable,
+	.count_voltages = regulator_fixed_count_voltages,
+	.list_voltage = regulator_fixed_list_voltage,
 };
 
 static int regulator_fixed_init(const struct device *dev)
@@ -99,6 +123,9 @@ static int regulator_fixed_init(const struct device *dev)
 }
 
 #define REGULATOR_FIXED_DEFINE(inst)                                              \
+	BUILD_ASSERT(DT_INST_PROP_OR(inst, regulator_min_microvolt, 0) ==         \
+		     DT_INST_PROP_OR(inst, regulator_max_microvolt, 0),           \
+		     "Regulator requires fixed voltages");                        \
 	static struct regulator_fixed_data data##inst;                            \
                                                                                   \
 	static const struct regulator_fixed_config config##inst = {               \

dts/bindings/regulator/regulator-fixed.yaml

@@ -11,6 +11,8 @@ include:
       - regulator-name
       - regulator-boot-on
       - regulator-always-on
+      - regulator-min-microvolt
+      - regulator-max-microvolt
 
 compatible: "regulator-fixed"
 

include/zephyr/drivers/regulator.h

@@ -2,6 +2,7 @@
  * Copyright (c) 2019-2020 Peter Bigot Consulting, LLC
  * Copyright (c) 2021 NXP
  * Copyright (c) 2022 Nordic Semiconductor ASA
+ * Copyright (c) 2023 EPAM Systems
  * SPDX-License-Identifier: Apache-2.0
  */
 
@@ -242,6 +243,28 @@ static inline bool regulator_common_is_init_enabled(const struct device *dev)
 	return (config->flags & REGULATOR_INIT_ENABLED) != 0U;
 }
 
+/**
+ * @brief Get minimum supported voltage.
+ *
+ * @param dev Regulator device instance.
+ * @param min_uv Where minimum voltage will be stored, in microvolts.
+ *
+ * @retval 0 If successful
+ * @retval -ENOENT If minimum voltage is not specified.
+ */
+static inline int regulator_common_get_min_voltage(const struct device *dev, int32_t *min_uv)
+{
+	const struct regulator_common_config *config =
+		(const struct regulator_common_config *)dev->config;
+
+	if (config->min_uv == INT32_MIN) {
+		return -ENOENT;
+	}
+
+	*min_uv = config->min_uv;
+	return 0;
+}
+
 /** @endcond */
 
 /**