Add driver for Maxim 77705 fuel gauge (part of max77705 PMIC)
providing power supply class information to userspace.

The driver is configured through DTS (battery and system related
settings).

Signed-off-by: Dzmitry Sankouski <dsankouski@gmail.com>

---
Changes for v6:
- add i2c init in driver
- initialize unintialized ret value with 0
- remove unused CAPACITY_SCALE_* constants
- max77705_*_convert: replace multiplication and divison with
  mult_frac helper to fix https://lore.kernel.org/oe-kbuild-all/202410111913.5ADtNHNM-lkp@intel.com/
- max77705_battery_settings: move out battery settings gathering and rename function
- probe: do regmap setup last, because if power_supply_get_battery_info
  fails, we're going to probe again and fail with i2c bus busy error
- remove MFD from commit message

Changes for v5:
- fix license
- use same hardware name in Kconfig and module descriptions
- fix email, and module author

Changes for v4:
- rework driver from scratch
- change word delimiters in filenames to "_"
- remove debugfs code
- cleanup header
---
 drivers/power/supply/Kconfig               |   7 +++
 drivers/power/supply/Makefile              |   1 +
 drivers/power/supply/max77705_fuel_gauge.c | 364 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/power/max77705_fuelgauge.h   |  60 +++++++++++++++++++++++
 4 files changed, 432 insertions(+)

diff --git a/drivers/power/supply/Kconfig b/drivers/power/supply/Kconfig
index 66264036b65d..9a3b17036ddc 100644
--- a/drivers/power/supply/Kconfig
+++ b/drivers/power/supply/Kconfig
@@ -589,6 +589,13 @@ config CHARGER_MAX77705
 	help
 	  Say Y to enable support for the Maxim MAX77705 battery charger.
 
+config FUEL_GAUGE_MAX77705
+	tristate "Maxim MAX77705 fuel gauge driver"
+	depends on MFD_MAX77705
+	default n
+	help
+	  Say Y to enable support for MAXIM MAX77705 fuel gauge driver.
+
 config CHARGER_MAX77976
 	tristate "Maxim MAX77976 battery charger driver"
 	depends on I2C
diff --git a/drivers/power/supply/Makefile b/drivers/power/supply/Makefile
index 85d65b7aee1c..997049fc1795 100644
--- a/drivers/power/supply/Makefile
+++ b/drivers/power/supply/Makefile
@@ -81,6 +81,7 @@ obj-$(CONFIG_CHARGER_DETECTOR_MAX14656)	+= max14656_charger_detector.o
 obj-$(CONFIG_CHARGER_MAX77650)	+= max77650-charger.o
 obj-$(CONFIG_CHARGER_MAX77693)	+= max77693_charger.o
 obj-$(CONFIG_CHARGER_MAX77705)	+= max77705_charger.o
+obj-$(CONFIG_FUEL_GAUGE_MAX77705)	+= max77705_fuel_gauge.o
 obj-$(CONFIG_CHARGER_MAX77976)	+= max77976_charger.o
 obj-$(CONFIG_CHARGER_MAX8997)	+= max8997_charger.o
 obj-$(CONFIG_CHARGER_MAX8998)	+= max8998_charger.o
diff --git a/drivers/power/supply/max77705_fuel_gauge.c b/drivers/power/supply/max77705_fuel_gauge.c
new file mode 100644
index 000000000000..a62111bb3cc0
--- /dev/null
+++ b/drivers/power/supply/max77705_fuel_gauge.c
@@ -0,0 +1,364 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Copyright (C) 2024 Dzmitry Sankouski <dsankouski@gmail>
+//
+// Fuel gauge driver for MAXIM 77705 charger/power-supply.
+
+#include <linux/i2c.h>
+#include <linux/interrupt.h>
+#include <linux/mfd/max77693-common.h>
+#include <linux/mfd/max77705-private.h>
+#include <linux/power/max77705_fuelgauge.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/power_supply.h>
+#include <linux/regmap.h>
+
+#define I2C_ADDR_FG     0x36
+
+static const char *max77705_fuelgauge_model		= "max77705";
+static const char *max77705_fuelgauge_manufacturer	= "Maxim Integrated";
+
+static const struct regmap_config max77705_fg_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.max_register = MAX77705_FG_END,
+};
+
+static enum power_supply_property max77705_fuelgauge_props[] = {
+	POWER_SUPPLY_PROP_STATUS,
+	POWER_SUPPLY_PROP_PRESENT,
+	POWER_SUPPLY_PROP_VOLTAGE_NOW,
+	POWER_SUPPLY_PROP_VOLTAGE_OCV,
+	POWER_SUPPLY_PROP_VOLTAGE_AVG,
+	POWER_SUPPLY_PROP_CURRENT_NOW,
+	POWER_SUPPLY_PROP_CURRENT_AVG,
+	POWER_SUPPLY_PROP_CHARGE_NOW,
+	POWER_SUPPLY_PROP_CHARGE_FULL,
+	POWER_SUPPLY_PROP_CHARGE_FULL_DESIGN,
+	POWER_SUPPLY_PROP_CAPACITY,
+	POWER_SUPPLY_PROP_TEMP,
+	POWER_SUPPLY_PROP_TIME_TO_EMPTY_NOW,
+	POWER_SUPPLY_PROP_TIME_TO_FULL_NOW,
+};
+
+static int max77705_fg_read_reg(struct max77705_fuelgauge_data *fuelgauge,
+				unsigned int reg, unsigned int *val)
+{
+	struct regmap *regmap = fuelgauge->regmap;
+	u8 data[2];
+	int ret;
+
+	ret = regmap_noinc_read(regmap, reg, data, sizeof(data));
+	if (ret < 0)
+		return ret;
+
+	*val = (data[1] << 8) + data[0];
+
+	return 0;
+}
+
+static int max77705_fg_read_temp(struct max77705_fuelgauge_data *fuelgauge,
+				 int *val)
+{
+	struct regmap *regmap = fuelgauge->regmap;
+	u8 data[2] = { 0, 0 };
+	int ret, temperature = 0;
+
+	ret = regmap_noinc_read(regmap, TEMPERATURE_REG, data, sizeof(data));
+	if (ret < 0)
+		return ret;
+
+	if (data[1] & BIT(7))
+		temperature = ((~(data[1])) & 0xFF) + 1;
+	else
+		temperature = data[1] & 0x7f;
+
+	temperature *= 10;
+	temperature += data[0] * 10 / 256;
+	*val = temperature;
+
+	return 0;
+}
+
+static int max77705_fg_check_battery_present(struct max77705_fuelgauge_data
+					     *fuelgauge, int *val)
+{
+	struct regmap *regmap = fuelgauge->regmap;
+	u8 status_data[2];
+	int ret;
+
+	ret = regmap_noinc_read(regmap, STATUS_REG, status_data, sizeof(status_data));
+	if (ret < 0)
+		return ret;
+
+	*val = !(status_data[0] & MAX77705_BAT_ABSENT_MASK);
+
+	return 0;
+}
+
+static int max77705_battery_get_status(struct max77705_fuelgauge_data *fuelgauge,
+					int *val)
+{
+	int current_now;
+	int am_i_supplied;
+	int ret;
+	unsigned int soc_rep;
+
+	am_i_supplied = power_supply_am_i_supplied(fuelgauge->psy_fg);
+	if (am_i_supplied) {
+		if (am_i_supplied == -ENODEV) {
+			dev_err(fuelgauge->dev,
+				"power supply not found, fall back to current-based method\n");
+		} else {
+			*val = POWER_SUPPLY_STATUS_CHARGING;
+			return 0;
+		}
+	}
+	ret = max77705_fg_read_reg(fuelgauge, SOCREP_REG, &soc_rep);
+	if (ret)
+		return ret;
+
+	if (soc_rep < 100) {
+		ret = max77705_fg_read_reg(fuelgauge, CURRENT_REG, &current_now);
+		if (ret)
+			return ret;
+
+		if (current_now > 0)
+			*val = POWER_SUPPLY_STATUS_CHARGING;
+		else if (current_now < 0)
+			*val = POWER_SUPPLY_STATUS_DISCHARGING;
+		else
+			*val = POWER_SUPPLY_STATUS_NOT_CHARGING;
+	} else {
+		*val = POWER_SUPPLY_STATUS_FULL;
+	}
+
+	return 0;
+}
+
+static void max77705_unit_adjustment(struct max77705_fuelgauge_data *fuelgauge,
+					 enum power_supply_property psp,
+					 union power_supply_propval *val)
+{
+	const unsigned int base_unit_conversion = 1000;
+
+	switch (psp) {
+	case POWER_SUPPLY_PROP_VOLTAGE_NOW:
+	case POWER_SUPPLY_PROP_VOLTAGE_OCV:
+	case POWER_SUPPLY_PROP_VOLTAGE_AVG:
+		val->intval = max77705_fg_vs_convert(val->intval);
+		break;
+	case POWER_SUPPLY_PROP_CURRENT_NOW:
+	case POWER_SUPPLY_PROP_CURRENT_AVG:
+		val->intval = max77705_fg_cs_convert(val->intval,
+						     fuelgauge->rsense_conductance);
+		break;
+	case POWER_SUPPLY_PROP_CHARGE_NOW:
+	case POWER_SUPPLY_PROP_CHARGE_FULL:
+	case POWER_SUPPLY_PROP_CHARGE_FULL_DESIGN:
+		val->intval *= base_unit_conversion;
+		break;
+	case POWER_SUPPLY_PROP_CAPACITY:
+		val->intval = min(val->intval, 100);
+		break;
+	default:
+		dev_dbg(fuelgauge->dev,
+			"%s: no need for unit conversion %d\n", __func__, psp);
+	}
+}
+
+static int max77705_fg_get_property(struct power_supply *psy,
+				    enum power_supply_property psp,
+				    union power_supply_propval *val)
+{
+	struct max77705_fuelgauge_data *fuelgauge =
+	    power_supply_get_drvdata(psy);
+	int ret = 0;
+
+	switch (psp) {
+	case POWER_SUPPLY_PROP_STATUS:
+		ret = max77705_battery_get_status(fuelgauge, &val->intval);
+		break;
+	case POWER_SUPPLY_PROP_PRESENT:
+		ret = max77705_fg_check_battery_present(fuelgauge, &val->intval);
+		break;
+	case POWER_SUPPLY_PROP_VOLTAGE_NOW:
+		ret = max77705_fg_read_reg(fuelgauge, VCELL_REG, &val->intval);
+		break;
+	case POWER_SUPPLY_PROP_VOLTAGE_OCV:
+		ret = max77705_fg_read_reg(fuelgauge, VFOCV_REG, &val->intval);
+		break;
+	case POWER_SUPPLY_PROP_VOLTAGE_AVG:
+		ret = max77705_fg_read_reg(fuelgauge, AVR_VCELL_REG, &val->intval);
+		break;
+	case POWER_SUPPLY_PROP_CURRENT_NOW:
+		ret = max77705_fg_read_reg(fuelgauge, CURRENT_REG, &val->intval);
+		break;
+	case POWER_SUPPLY_PROP_CURRENT_AVG:
+		ret = max77705_fg_read_reg(fuelgauge, AVG_CURRENT_REG, &val->intval);
+		break;
+	case POWER_SUPPLY_PROP_CHARGE_NOW:
+		ret = max77705_fg_read_reg(fuelgauge, REMCAP_REP_REG, &val->intval);
+		break;
+	case POWER_SUPPLY_PROP_CHARGE_FULL:
+		ret = max77705_fg_read_reg(fuelgauge, FULLCAP_REP_REG, &val->intval);
+		break;
+	case POWER_SUPPLY_PROP_CHARGE_FULL_DESIGN:
+		ret = max77705_fg_read_reg(fuelgauge, DESIGNCAP_REG, &val->intval);
+		break;
+	case POWER_SUPPLY_PROP_CAPACITY:
+		ret = max77705_fg_read_reg(fuelgauge, SOCREP_REG, &val->intval);
+		break;
+	case POWER_SUPPLY_PROP_TEMP:
+		ret = max77705_fg_read_temp(fuelgauge, &val->intval);
+		break;
+	case POWER_SUPPLY_PROP_TIME_TO_EMPTY_NOW:
+		ret = max77705_fg_read_reg(fuelgauge, TIME_TO_EMPTY_REG, &val->intval);
+		break;
+	case POWER_SUPPLY_PROP_TIME_TO_FULL_NOW:
+		ret = max77705_fg_read_reg(fuelgauge, TIME_TO_FULL_REG, &val->intval);
+		break;
+	case POWER_SUPPLY_PROP_CYCLE_COUNT:
+		ret = max77705_fg_read_reg(fuelgauge, CYCLES_REG, &val->intval);
+		break;
+	case POWER_SUPPLY_PROP_MODEL_NAME:
+		val->strval = max77705_fuelgauge_model;
+		break;
+	case POWER_SUPPLY_PROP_MANUFACTURER:
+		val->strval = max77705_fuelgauge_manufacturer;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	if (ret)
+		return ret;
+
+	max77705_unit_adjustment(fuelgauge, psp, val);
+
+	return 0;
+}
+
+static const struct power_supply_desc max77705_fg_desc = {
+	.name = "max77705-fuel-gauge",
+	.type = POWER_SUPPLY_TYPE_BATTERY,
+	.properties = max77705_fuelgauge_props,
+	.num_properties = ARRAY_SIZE(max77705_fuelgauge_props),
+	.get_property = max77705_fg_get_property,
+};
+
+static int max77705_fg_set_charge_design(struct regmap *regmap, int value)
+{
+	u8 data[2];
+	int value_mah;
+
+	value_mah = value / 1000;
+	data[0] = value_mah & 0xFF;
+	data[1] = (value_mah >> 8) & 0xFF;
+
+	return regmap_noinc_write(regmap, DESIGNCAP_REG, data, sizeof(data));
+}
+
+static int max77705_write_bat_info(struct max77705_fuelgauge_data *fuelgauge)
+{
+	struct power_supply_battery_info *info = fuelgauge->bat_info;
+
+	if (info->energy_full_design_uwh != info->charge_full_design_uah) {
+		if (info->charge_full_design_uah == -EINVAL)
+			dev_warn(fuelgauge->dev, "missing battery:charge-full-design-microamp-hours\n");
+		return max77705_fg_set_charge_design(fuelgauge->regmap,
+						info->charge_full_design_uah);
+	}
+
+	return 0;
+}
+
+static int max77705_fuelgauge_parse_dt(struct max77705_fuelgauge_data
+				       *fuelgauge)
+{
+	struct device *dev = fuelgauge->dev;
+	struct device_node *np = dev->of_node;
+	int ret;
+	unsigned int rsense;
+
+	if (!np) {
+		dev_err(dev, "no fuelgauge OF node\n");
+		return -EINVAL;
+	}
+	ret = of_property_read_u32(np, "shunt-resistor-micro-ohms",
+				   &rsense);
+	if (ret < 0) {
+		dev_warn(dev, "No shunt-resistor-micro-ohms property, assume default\n");
+		fuelgauge->rsense_conductance = 100;
+	} else
+		fuelgauge->rsense_conductance = 1000000 / rsense; /* rsense conductance in Ohm^-1 */
+
+	return 0;
+}
+
+static int max77705_fuelgauge_probe(struct platform_device *pdev)
+{
+	struct i2c_client *i2c_fg;
+	struct max77693_dev *max77705 = dev_get_drvdata(pdev->dev.parent);
+	struct max77705_fuelgauge_data *fuelgauge;
+	struct power_supply_config fuelgauge_cfg = { };
+	struct device *dev = &pdev->dev;
+	int ret = 0;
+
+	fuelgauge = devm_kzalloc(dev, sizeof(*fuelgauge), GFP_KERNEL);
+	if (!fuelgauge)
+		return -ENOMEM;
+
+	fuelgauge->dev = dev;
+
+	ret = max77705_fuelgauge_parse_dt(fuelgauge);
+	if (ret < 0)
+		return ret;
+
+	fuelgauge_cfg.drv_data = fuelgauge;
+	fuelgauge_cfg.of_node = fuelgauge->dev->of_node;
+
+	fuelgauge->psy_fg = devm_power_supply_register(&pdev->dev,
+							&max77705_fg_desc,
+							&fuelgauge_cfg);
+
+	if (IS_ERR(fuelgauge->psy_fg))
+		return PTR_ERR(fuelgauge->psy_fg);
+
+	ret = power_supply_get_battery_info(fuelgauge->psy_fg,
+					&fuelgauge->bat_info);
+
+	if (ret)
+		return ret;
+
+	i2c_fg = devm_i2c_new_dummy_device(max77705->dev, max77705->i2c->adapter,
+						I2C_ADDR_FG);
+
+	if (IS_ERR(i2c_fg))
+		return PTR_ERR(i2c_fg);
+
+	fuelgauge->regmap = devm_regmap_init_i2c(i2c_fg,
+						   &max77705_fg_regmap_config);
+
+	return max77705_write_bat_info(fuelgauge);
+}
+
+static const struct of_device_id max77705_fg_of_match[] = {
+	{ .compatible = "maxim,max77705-fuel-gauge" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, max77705_fg_of_match);
+
+static struct platform_driver max77705_fuelgauge_driver = {
+	.driver = {
+		.name = "max77705-fuel-gauge",
+		.of_match_table = max77705_fg_of_match,
+	},
+	.probe = max77705_fuelgauge_probe,
+};
+module_platform_driver(max77705_fuelgauge_driver);
+
+MODULE_DESCRIPTION("Maxim MAX77705 Fuel Gauge Driver");
+MODULE_AUTHOR("Dzmitry Sankouski <dsankouski@gmail>");
+MODULE_LICENSE("GPL");
diff --git a/include/linux/power/max77705_fuelgauge.h b/include/linux/power/max77705_fuelgauge.h
new file mode 100644
index 000000000000..daa28dff4c00
--- /dev/null
+++ b/include/linux/power/max77705_fuelgauge.h
@@ -0,0 +1,60 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+//
+// Copyright (C) 2024 Dzmitry Sankouski <dsankouski@gmail.org>
+//
+// Fuel gauge driver header for MAXIM 77705 charger/power-supply.
+
+#ifndef __MAX77705_FUELGAUGE_H
+#define __MAX77705_FUELGAUGE_H __FILE__
+
+#include <linux/regmap.h>
+#include <linux/platform_device.h>
+#include <linux/power_supply.h>
+
+#define ALERT_EN			4
+// Current and capacity values are displayed as a voltage
+// and must be divided by the sense resistor to determine Amps or Amp-hours.
+// This should be applied to all current, charge, energy registers,
+// except ModelGauge m5 Algorithm related ones.
+// current sense resolution
+#define MAX77705_FG_CS_ADC_RESOLUTION	15625 // 1.5625 microvolts
+// voltage sense resolution
+#define MAX77705_FG_VS_ADC_RESOLUTION	78125 // 78.125 microvolts
+// CONFIG_REG register
+#define MAX77705_SOC_ALERT_EN_MASK	BIT(2)
+// When set to 1, external temperature measurements should be written from the host
+#define MAX77705_TEX_MASK		BIT(8)
+// Enable Thermistor
+#define MAX77705_ETHRM_MASK		BIT(5)
+// CONFIG2_REG register
+#define MAX77705_AUTO_DISCHARGE_EN_MASK BIT(9)
+// STATUS_REG register
+#define MAX77705_BAT_ABSENT_MASK	BIT(3)
+
+// @brief Convert voltage register value to micro volts
+// @param reg_val - register value
+// @return voltage in micro Volts
+inline u64 max77705_fg_vs_convert(u16 reg_val)
+{
+	return mult_frac(reg_val, MAX77705_FG_VS_ADC_RESOLUTION, 1000);
+}
+
+// @brief Convert current register value to micro volts
+// @param reg_val - register value
+// @param rsense_conductance - current sense resistor conductance in Ohm^-1
+// @return voltage in micro Volts
+inline s32 max77705_fg_cs_convert(s16 reg_val, u32 rsense_conductance)
+{
+	return mult_frac(reg_val * rsense_conductance, MAX77705_FG_CS_ADC_RESOLUTION,
+			 10000);
+}
+
+struct max77705_fuelgauge_data {
+	struct device *dev;
+	struct regmap *regmap;
+	struct power_supply *psy_fg;
+	struct power_supply_battery_info *bat_info;
+	u32 rsense_conductance;
+};
+
+#endif // __MAX77705_FUELGAUGE_H

-- 
2.39.2