hwmon: (nct7802) Make temperature/voltage sensors configurable

This change allows LTD and RTD inputs to be configured via
device tree bindings. If the DT bindings are not present or
invalid, the input configuration is not modified and left at
HW defaults.

Signed-off-by: Oskar Senft <osk@google.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20211020164213.174597-2-osk@google.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Author: osenft

drivers/hwmon/nct7802.c

@@ -51,6 +51,23 @@ static const u8 REG_VOLTAGE_LIMIT_MSB_SHIFT[2][5] = {
 #define REG_CHIP_ID		0xfe
 #define REG_VERSION_ID		0xff
 
+/*
+ * Resistance temperature detector (RTD) modes according to 7.2.32 Mode
+ * Selection Register
+ */
+#define RTD_MODE_CURRENT	0x1
+#define RTD_MODE_THERMISTOR	0x2
+#define RTD_MODE_VOLTAGE	0x3
+
+#define MODE_RTD_MASK		0x3
+#define MODE_LTD_EN		0x40
+
+/*
+ * Bit offset for sensors modes in REG_MODE.
+ * Valid for index 0..2, indicating RTD1..3.
+ */
+#define MODE_BIT_OFFSET_RTD(index) ((index) * 2)
+
 /*
  * Data structures and manipulation thereof
  */
@@ -1038,7 +1055,112 @@ static const struct regmap_config nct7802_regmap_config = {
 	.volatile_reg = nct7802_regmap_is_volatile,
 };
 
-static int nct7802_init_chip(struct nct7802_data *data)
+static int nct7802_get_channel_config(struct device *dev,
+				      struct device_node *node, u8 *mode_mask,
+				      u8 *mode_val)
+{
+	u32 reg;
+	const char *type_str, *md_str;
+	u8 md;
+
+	if (!node->name || of_node_cmp(node->name, "channel"))
+		return 0;
+
+	if (of_property_read_u32(node, "reg", &reg)) {
+		dev_err(dev, "Could not read reg value for '%s'\n",
+			node->full_name);
+		return -EINVAL;
+	}
+
+	if (reg > 3) {
+		dev_err(dev, "Invalid reg (%u) in '%s'\n", reg,
+			node->full_name);
+		return -EINVAL;
+	}
+
+	if (reg == 0) {
+		if (!of_device_is_available(node))
+			*mode_val &= ~MODE_LTD_EN;
+		else
+			*mode_val |= MODE_LTD_EN;
+		*mode_mask |= MODE_LTD_EN;
+		return 0;
+	}
+
+	/* At this point we have reg >= 1 && reg <= 3 */
+
+	if (!of_device_is_available(node)) {
+		*mode_val &= ~(MODE_RTD_MASK << MODE_BIT_OFFSET_RTD(reg - 1));
+		*mode_mask |= MODE_RTD_MASK << MODE_BIT_OFFSET_RTD(reg - 1);
+		return 0;
+	}
+
+	if (of_property_read_string(node, "sensor-type", &type_str)) {
+		dev_err(dev, "No type for '%s'\n", node->full_name);
+		return -EINVAL;
+	}
+
+	if (!strcmp(type_str, "voltage")) {
+		*mode_val |= (RTD_MODE_VOLTAGE & MODE_RTD_MASK)
+			     << MODE_BIT_OFFSET_RTD(reg - 1);
+		*mode_mask |= MODE_RTD_MASK << MODE_BIT_OFFSET_RTD(reg - 1);
+		return 0;
+	}
+
+	if (strcmp(type_str, "temperature")) {
+		dev_err(dev, "Invalid type '%s' for '%s'\n", type_str,
+			node->full_name);
+		return -EINVAL;
+	}
+
+	if (reg == 3) {
+		/* RTD3 only supports thermistor mode */
+		md = RTD_MODE_THERMISTOR;
+	} else {
+		if (of_property_read_string(node, "temperature-mode",
+					    &md_str)) {
+			dev_err(dev, "No mode for '%s'\n", node->full_name);
+			return -EINVAL;
+		}
+
+		if (!strcmp(md_str, "thermal-diode"))
+			md = RTD_MODE_CURRENT;
+		else if (!strcmp(md_str, "thermistor"))
+			md = RTD_MODE_THERMISTOR;
+		else {
+			dev_err(dev, "Invalid mode '%s' for '%s'\n", md_str,
+				node->full_name);
+			return -EINVAL;
+		}
+	}
+
+	*mode_val |= (md & MODE_RTD_MASK) << MODE_BIT_OFFSET_RTD(reg - 1);
+	*mode_mask |= MODE_RTD_MASK << MODE_BIT_OFFSET_RTD(reg - 1);
+
+	return 0;
+}
+
+static int nct7802_configure_channels(struct device *dev,
+				      struct nct7802_data *data)
+{
+	/* Enable local temperature sensor by default */
+	u8 mode_mask = MODE_LTD_EN, mode_val = MODE_LTD_EN;
+	struct device_node *node;
+	int err;
+
+	if (dev->of_node) {
+		for_each_child_of_node(dev->of_node, node) {
+			err = nct7802_get_channel_config(dev, node, &mode_mask,
+							 &mode_val);
+			if (err)
+				return err;
+		}
+	}
+
+	return regmap_update_bits(data->regmap, REG_MODE, mode_mask, mode_val);
+}
+
+static int nct7802_init_chip(struct device *dev, struct nct7802_data *data)
 {
 	int err;
 
@@ -1047,8 +1169,7 @@ static int nct7802_init_chip(struct nct7802_data *data)
 	if (err)
 		return err;
 
-	/* Enable local temperature sensor */
-	err = regmap_update_bits(data->regmap, REG_MODE, 0x40, 0x40);
+	err = nct7802_configure_channels(dev, data);
 	if (err)
 		return err;
 
@@ -1074,7 +1195,7 @@ static int nct7802_probe(struct i2c_client *client)
 	mutex_init(&data->access_lock);
 	mutex_init(&data->in_alarm_lock);
 
-	ret = nct7802_init_chip(data);
+	ret = nct7802_init_chip(dev, data);
 	if (ret < 0)
 		return ret;