Message-ID: <aXq7NohfIy3c5AWL@venus>
Date: Thu, 29 Jan 2026 02:59:39 +0100
From: Sebastian Reichel <sebastian.reichel@...labora.com>
To: Kaustabh Chakraborty <kauschluss@...root.org>
Cc: Yassine Oudjana <y.oudjana@...tonmail.com>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, linux-pm@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] power: supply: add support for S2MU005 battery fuel
 gauge device

Hi,

On Mon, Jan 26, 2026 at 09:09:49PM +0530, Kaustabh Chakraborty wrote:
> From: Yassine Oudjana <y.oudjana@...tonmail.com>
> 
> Samsung's S2MU005 PMIC, which contains battery charger functionality
> also includes a battery fuel gauge device, which is separate from the
> PMIC itself, and typically connected to an I2C bus. Add a generic driver
> to support said device.
> 
> Signed-off-by: Yassine Oudjana <y.oudjana@...tonmail.com>
> Co-developed-by: Kaustabh Chakraborty <kauschluss@...root.org>
> Signed-off-by: Kaustabh Chakraborty <kauschluss@...root.org>
> ---
>  drivers/power/supply/Kconfig           |   9 ++
>  drivers/power/supply/Makefile          |   1 +
>  drivers/power/supply/s2mu005-battery.c | 234 +++++++++++++++++++++++++++++++++
>  3 files changed, 244 insertions(+)
> 
> diff --git a/drivers/power/supply/Kconfig b/drivers/power/supply/Kconfig
> index 92f9f7aae92f2..a5777309b1f62 100644
> --- a/drivers/power/supply/Kconfig
> +++ b/drivers/power/supply/Kconfig
> @@ -229,6 +229,15 @@ config BATTERY_SAMSUNG_SDI
>  	  Say Y to enable support for Samsung SDI battery data.
>  	  These batteries are used in Samsung mobile phones.
>  
> +config BATTERY_S2MU005
> +	tristate "Samsung S2MU005 PMIC fuel gauge driver"
> +	help
> +	  Say Y to enable support for the Samsung S2MU005 PMIC integrated
> +	  fuel gauge, which works indepenently of the PMIC battery charger
> +	  counterpart, and reports battery metrics.
> +
> +	  This driver, if built as a module, will be called s2mu005-fuel-gauge.
> +
>  config BATTERY_COLLIE
>  	tristate "Sharp SL-5500 (collie) battery"
>  	depends on SA1100_COLLIE && MCP_UCB1200
> diff --git a/drivers/power/supply/Makefile b/drivers/power/supply/Makefile
> index 4b79d5abc49a7..cd061887c1727 100644
> --- a/drivers/power/supply/Makefile
> +++ b/drivers/power/supply/Makefile
> @@ -40,6 +40,7 @@ obj-$(CONFIG_BATTERY_PMU)	+= pmu_battery.o
>  obj-$(CONFIG_BATTERY_QCOM_BATTMGR)	+= qcom_battmgr.o
>  obj-$(CONFIG_BATTERY_OLPC)	+= olpc_battery.o
>  obj-$(CONFIG_BATTERY_SAMSUNG_SDI)	+= samsung-sdi-battery.o
> +obj-$(CONFIG_BATTERY_S2MU005)	+= s2mu005-battery.o
>  obj-$(CONFIG_BATTERY_COLLIE)	+= collie_battery.o
>  obj-$(CONFIG_BATTERY_INGENIC)	+= ingenic-battery.o
>  obj-$(CONFIG_BATTERY_INTEL_DC_TI) += intel_dc_ti_battery.o
> diff --git a/drivers/power/supply/s2mu005-battery.c b/drivers/power/supply/s2mu005-battery.c
> new file mode 100644
> index 0000000000000..914308e82683b
> --- /dev/null
> +++ b/drivers/power/supply/s2mu005-battery.c
> @@ -0,0 +1,234 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Battery Fuel Gauge Driver for Samsung S2MU005 PMIC.
> + *
> + * Copyright (C) 2015 Samsung Electronics
> + * Copyright (C) 2023 Yassine Oudjana <y.oudjana@...tonmail.com>
> + * Copyright (C) 2025 Kaustabh Chakraborty <kauschluss@...root.org>
> + */
> +
> +#include <linux/delay.h>
> +#include <linux/i2c.h>
> +#include <linux/interrupt.h>
> +#include <linux/irq.h>
> +#include <linux/of.h>
> +#include <linux/power_supply.h>
> +#include <linux/regmap.h>
> +
> +#define S2MU005_FG_REG_STATUS		0x00
> +#define S2MU005_FG_REG_IRQ		0x02
> +#define S2MU005_FG_REG_RVBAT		0x04
> +#define S2MU005_FG_REG_RCUR_CC		0x06
> +#define S2MU005_FG_REG_RSOC		0x08
> +#define S2MU005_FG_REG_MONOUT		0x0a
> +#define S2MU005_FG_REG_MONOUT_SEL	0x0c
> +#define S2MU005_FG_REG_RBATCAP		0x0e
> +#define S2MU005_FG_REG_RZADJ		0x12
> +#define S2MU005_FG_REG_RBATZ0		0x16
> +#define S2MU005_FG_REG_RBATZ1		0x18
> +#define S2MU005_FG_REG_IRQ_LVL		0x1a
> +#define S2MU005_FG_REG_START		0x1e
> +
> +struct s2mu005_fg {
> +	struct device *dev;
> +	struct regmap *regmap;
> +	struct power_supply *psy;
> +};
> +
> +static const struct regmap_config s2mu005_fg_regmap_config = {
> +	.reg_bits = 8,
> +	.val_bits = 8,
> +};

Looks like all register addresses are 2 byte aligned and you are
always using regmap_raw_read to get 16bit values. So just use
.val_bits = 16 here?

> +static irqreturn_t s2mu005_handle_irq(int irq, void *data)
> +{
> +	struct s2mu005_fg *priv = data;
> +
> +	msleep(100);
> +	power_supply_changed(priv->psy);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static int s2mu005_fg_get_voltage_now(struct s2mu005_fg *priv, int *value)
> +{
> +	struct regmap *regmap = priv->regmap;
> +	u16 reg;
> +	int ret;
> +
> +	ret = regmap_raw_read(regmap, S2MU005_FG_REG_RVBAT, &reg, sizeof(reg));
> +	if (ret < 0) {
> +		dev_err(priv->dev, "failed to read voltage register (%d)\n", ret);
> +		return ret;
> +	}
> +
> +	*value = ((unsigned long)reg * 1000000) >> 13; /* uV */
> +
> +	return 0;
> +}
> +
> +static int s2mu005_fg_get_current_now(struct s2mu005_fg *priv, int *value)
> +{
> +	struct regmap *regmap = priv->regmap;
> +	s16 reg;
> +	int ret;
> +
> +	ret = regmap_raw_read(regmap, S2MU005_FG_REG_RCUR_CC, &reg, sizeof(reg));
> +	if (ret < 0) {
> +		dev_err(priv->dev, "failed to read current register (%d)\n", ret);
> +		return ret;
> +	}
> +
> +	*value = -((long)reg * 1000000) >> 12; /* uA */
> +
> +	return 0;
> +}
> +
> +static int s2mu005_fg_get_capacity(struct s2mu005_fg *priv, int *value)
> +{
> +	struct regmap *regmap = priv->regmap;
> +	s16 reg;
> +	int ret;
> +
> +	ret = regmap_raw_read(regmap, S2MU005_FG_REG_RSOC, &reg, sizeof(reg));
> +	if (ret < 0) {
> +		dev_err(priv->dev, "failed to read capacity register (%d)\n", ret);
> +		return ret;
> +	}
> +
> +	*value = (reg * 100) >> 14; /* percentage */
> +
> +	return 0;
> +}
> +
> +static int s2mu005_fg_get_status(struct s2mu005_fg *priv, int *value)
> +{
> +	int current_now;
> +	int capacity;
> +	int ret;
> +
> +	ret = s2mu005_fg_get_current_now(priv, &current_now);
> +	if (ret)
> +		return ret;
> +
> +	if (current_now <= 0) {
> +		*value = POWER_SUPPLY_STATUS_DISCHARGING;
> +		return 0;
> +	}
> +
> +	ret = s2mu005_fg_get_capacity(priv, &capacity);
> +	if (ret)
> +		return ret;
> +
> +	if (capacity < 90)
> +		*value = POWER_SUPPLY_STATUS_CHARGING;
> +	else
> +		*value = POWER_SUPPLY_STATUS_FULL;

Usually there is some kind of hysteresis that stops charging
when the battery is full and then restarts charging once the
battery drops under a certain capacity. As this code first
checks the current to determine if the battery is discharging
and only then checks if the battery is full - does your code
toggle between FULL and DISCHARGING?

> +	return 0;
> +}
> +
> +static const enum power_supply_property s2mu005_fg_properties[] = {
> +	POWER_SUPPLY_PROP_VOLTAGE_NOW,
> +	POWER_SUPPLY_PROP_CURRENT_NOW,
> +	POWER_SUPPLY_PROP_CAPACITY,
> +	POWER_SUPPLY_PROP_STATUS,
> +};
> +
> +static int s2mu005_fg_get_property(struct power_supply *psy,
> +				   enum power_supply_property psp,
> +				   union power_supply_propval *val)
> +{
> +	struct s2mu005_fg *priv = power_supply_get_drvdata(psy);
> +	int ret = 0;
> +
> +	switch (psp) {
> +	case POWER_SUPPLY_PROP_VOLTAGE_NOW:
> +		ret = s2mu005_fg_get_voltage_now(priv, &val->intval);
> +		break;
> +	case POWER_SUPPLY_PROP_CURRENT_NOW:
> +		ret = s2mu005_fg_get_current_now(priv, &val->intval);
> +		break;
> +	case POWER_SUPPLY_PROP_CAPACITY:
> +		ret = s2mu005_fg_get_capacity(priv, &val->intval);
> +		break;
> +	case POWER_SUPPLY_PROP_STATUS:
> +		ret = s2mu005_fg_get_status(priv, &val->intval);
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	return ret;
> +}
> +
> +static const struct power_supply_desc s2mu005_fg_desc = {
> +	.name = "s2mu005-fuel-gauge",
> +	.type = POWER_SUPPLY_TYPE_BATTERY,
> +	.properties = s2mu005_fg_properties,
> +	.num_properties = ARRAY_SIZE(s2mu005_fg_properties),
> +	.get_property = s2mu005_fg_get_property,
> +};
> +
> +static int s2mu005_fg_i2c_probe(struct i2c_client *client)
> +{
> +	struct device *dev = &client->dev;
> +	struct s2mu005_fg *priv;
> +	struct power_supply_config psy_cfg = {};
> +	const struct power_supply_desc *psy_desc;
> +	int flags;
> +	int ret;
> +
> +	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return dev_err_probe(dev, -ENOMEM,
> +				     "failed to allocate driver private\n");

Do not print error messages for -ENOMEM.

> +
> +	dev_set_drvdata(dev, priv);
> +	priv->dev = dev;
> +
> +	priv->regmap = devm_regmap_init_i2c(client, &s2mu005_fg_regmap_config);
> +	if (IS_ERR(priv->regmap))
> +		return dev_err_probe(dev, PTR_ERR(priv->regmap),
> +				     "failed to initialize regmap\n");
> +
> +	psy_desc = device_get_match_data(dev);
> +
> +	psy_cfg.drv_data = priv;
> +	priv->psy = devm_power_supply_register(priv->dev, psy_desc, &psy_cfg);
> +	if (IS_ERR(priv->psy))
> +		return dev_err_probe(dev, PTR_ERR(priv->psy),
> +				     "failed to register power supply subsystem\n");
> +
> +	flags = irq_get_trigger_type(client->irq);

This is not needed. By not specifying the trigger type the irq core
code will do this internally.

> +	ret = devm_request_threaded_irq(priv->dev, client->irq, NULL,
> +					s2mu005_handle_irq, IRQF_ONESHOT | flags,
> +					psy_desc->name, priv);
> +	if (ret)
> +		dev_err_probe(dev, ret, "failed to request IRQ\n");
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id s2mu005_fg_of_match_table[] = {
> +	{
> +		.compatible = "samsung,s2mu005-fuel-gauge",
> +		.data = &s2mu005_fg_desc,
> +	}, { },

Please put the terminator into its own line and remove the final ,

> +};
> +MODULE_DEVICE_TABLE(of, s2mu005_fg_of_match_table);
> +
> +static struct i2c_driver s2mu005_fg_i2c_driver = {
> +	.probe = s2mu005_fg_i2c_probe,
> +	.driver = {
> +		.name = "s2mu005-fuel-gauge",
> +		.of_match_table = of_match_ptr(s2mu005_fg_of_match_table),

Remove of_match_ptr().

> +	},
> +};
> +module_i2c_driver(s2mu005_fg_i2c_driver);
> +
> +MODULE_DESCRIPTION("Samsung S2MU005 PMIC Battery Fuel Gauge Driver");
> +MODULE_AUTHOR("Yassine Oudjana <y.oudjana@...tonmail.com>");
> +MODULE_AUTHOR("Kaustabh Chakraborty <kauschluss@...root.org>");
> +MODULE_LICENSE("GPL");

Greetings,

-- Sebastian

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