power: supply: max1720x: add support for reading internal and thermistor temperatures

If enabled in the nPackCfg register, the Temp1, Temp2 and IntTemp registers
contain the temperature readings from the AIN1 thermistor, AIN2 thermistor
and internal die temperature respectively. Registers are shared between SBS
and normal IC functions and are always readable regardless of IC settings.

Signed-off-by: Dimitri Fedrau <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sebastian Reichel <[email protected]>

Author: DimitriFedrau

Documentation/ABI/testing/sysfs-class-power-max1720x

@@ -0,0 +1,32 @@
+What:		/sys/class/power_supply/max1720x/temp_ain1
+Date:		January 2025
+KernelVersion:	6.14
+Contact:	Dimitri Fedrau <[email protected]>
+Description:
+		Reports the current temperature reading from AIN1 thermistor.
+
+		Access: Read
+
+		Valid values: Represented in 1/10 Degrees Celsius
+
+What:		/sys/class/power_supply/max1720x/temp_ain2
+Date:		January 2025
+KernelVersion:	6.14
+Contact:	Dimitri Fedrau <[email protected]>
+Description:
+		Reports the current temperature reading from AIN2 thermistor.
+
+		Access: Read
+
+		Valid values: Represented in 1/10 Degrees Celsius
+
+What:		/sys/class/power_supply/max1720x/temp_int
+Date:		January 2025
+KernelVersion:	6.14
+Contact:	Dimitri Fedrau <[email protected]>
+Description:
+		Reports the current temperature reading from internal die.
+
+		Access: Read
+
+		Valid values: Represented in 1/10 Degrees Celsius

drivers/power/supply/max1720x_battery.c

@@ -16,6 +16,11 @@
 
 #include <linux/unaligned.h>
 
+/* SBS compliant registers */
+#define MAX172XX_TEMP1			0x34
+#define MAX172XX_INT_TEMP		0x35
+#define MAX172XX_TEMP2			0x3B
+
 /* Nonvolatile registers */
 #define MAX1720X_NXTABLE0		0x80
 #define MAX1720X_NRSENSE		0xCF	/* RSense in 10^-5 Ohm */
@@ -113,11 +118,15 @@ static const struct regmap_config max1720x_regmap_cfg = {
 };
 
 static const struct regmap_range max1720x_nvmem_allow[] = {
+	regmap_reg_range(MAX172XX_TEMP1, MAX172XX_INT_TEMP),
+	regmap_reg_range(MAX172XX_TEMP2, MAX172XX_TEMP2),
 	regmap_reg_range(MAX1720X_NXTABLE0, MAX1720X_NDEVICE_NAME4),
 };
 
 static const struct regmap_range max1720x_nvmem_deny[] = {
-	regmap_reg_range(0x00, 0x7F),
+	regmap_reg_range(0x00, 0x33),
+	regmap_reg_range(0x36, 0x3A),
+	regmap_reg_range(0x3C, 0x7F),
 	regmap_reg_range(0xE0, 0xFF),
 };
 
@@ -388,6 +397,54 @@ static int max1720x_battery_get_property(struct power_supply *psy,
 	return ret;
 }
 
+static int max1720x_read_temp(struct device *dev, u8 reg, char *buf)
+{
+	struct power_supply *psy = dev_get_drvdata(dev);
+	struct max1720x_device_info *info = power_supply_get_drvdata(psy);
+	unsigned int val;
+	int ret;
+
+	ret = regmap_read(info->regmap_nv, reg, &val);
+	if (ret < 0)
+		return ret;
+
+	/*
+	 * Temperature in degrees Celsius starting at absolute zero, -273C or
+	 * 0K with an LSb of 0.1C
+	 */
+	return sysfs_emit(buf, "%d\n", val - 2730);
+}
+
+static ssize_t temp_ain1_show(struct device *dev, struct device_attribute *attr,
+			      char *buf)
+{
+	return max1720x_read_temp(dev, MAX172XX_TEMP1, buf);
+}
+
+static ssize_t temp_ain2_show(struct device *dev, struct device_attribute *attr,
+			      char *buf)
+{
+	return max1720x_read_temp(dev, MAX172XX_TEMP2, buf);
+}
+
+static ssize_t temp_int_show(struct device *dev, struct device_attribute *attr,
+			     char *buf)
+{
+	return max1720x_read_temp(dev, MAX172XX_INT_TEMP, buf);
+}
+
+static DEVICE_ATTR_RO(temp_ain1);
+static DEVICE_ATTR_RO(temp_ain2);
+static DEVICE_ATTR_RO(temp_int);
+
+static struct attribute *max1720x_attrs[] = {
+	&dev_attr_temp_ain1.attr,
+	&dev_attr_temp_ain2.attr,
+	&dev_attr_temp_int.attr,
+	NULL
+};
+ATTRIBUTE_GROUPS(max1720x);
+
 static
 int max1720x_nvmem_reg_read(void *priv, unsigned int off, void *val, size_t len)
 {
@@ -488,6 +545,7 @@ static int max1720x_probe(struct i2c_client *client)
 
 	psy_cfg.drv_data = info;
 	psy_cfg.fwnode = dev_fwnode(dev);
+	psy_cfg.attr_grp = max1720x_groups;
 	i2c_set_clientdata(client, info);
 	info->regmap = devm_regmap_init_i2c(client, &max1720x_regmap_cfg);
 	if (IS_ERR(info->regmap))