Message-ID: <71d816c5ed4ee2d13ec63b8fd4acd49f4e418284.camel@linaro.org>
Date: Thu, 22 Jan 2026 12:47:44 +0000
From: André Draszik <andre.draszik@...aro.org>
To: amitsd@...gle.com, Sebastian Reichel <sre@...nel.org>, Rob Herring	
 <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley	
 <conor+dt@...nel.org>, Lee Jones <lee@...nel.org>, Greg Kroah-Hartman	
 <gregkh@...uxfoundation.org>, Badhri Jagan Sridharan <badhri@...gle.com>, 
 Heikki Krogerus <heikki.krogerus@...ux.intel.com>, Peter Griffin
 <peter.griffin@...aro.org>, Tudor Ambarus	 <tudor.ambarus@...aro.org>, Alim
 Akhtar <alim.akhtar@...sung.com>
Cc: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-usb@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-samsung-soc@...r.kernel.org, RD
 Babiera <rdbabiera@...gle.com>, Kyle Tso <kyletso@...gle.com>
Subject: Re: [PATCH v4 4/5] power: supply: max77759: add charger driver

Hi Amit,

Thanks for your patches, just a few minor comments below.

On Wed, 2026-01-21 at 00:59 +0000, Amit Sunil Dhamne via B4 Relay wrote:
> From: Amit Sunil Dhamne <amitsd@...gle.com>
> 
> Add support for MAX77759 battery charger driver. This is a 4A 1-Cell
> Li+/LiPoly dual input switch mode charger. While the device can support
> USB & wireless charger inputs, this implementation only supports USB
> input. This implementation supports both buck and boost modes.
> 
> Signed-off-by: Amit Sunil Dhamne <amitsd@...gle.com>
> ---
>  MAINTAINERS                             |   6 +
>  drivers/power/supply/Kconfig            |  11 +
>  drivers/power/supply/Makefile           |   1 +
>  drivers/power/supply/max77759_charger.c | 737 ++++++++++++++++++++++++++++++++
>  4 files changed, 755 insertions(+)
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 0d044a58cbfe0f2b97f3682a86708e1ece108e9f..38354964a85c34611b1b54e20651b360f3b9c11e 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -15546,6 +15546,12 @@ F:	drivers/mfd/max77759.c
>  F:	drivers/nvmem/max77759-nvmem.c
>  F:	include/linux/mfd/max77759.h
>  
> +MAXIM MAX77759 BATTERY CHARGER DRIVER
> +M:	Amit Sunil Dhamne <amitsd@...gle.com>
> +L:	linux-kernel@...r.kernel.org
> +S:	Maintained
> +F:	drivers/power/supply/max77759_charger.c
> +
>  MAXIM MAX77802 PMIC REGULATOR DEVICE DRIVER
>  M:	Javier Martinez Canillas <javier@...hile0.org>
>  L:	linux-kernel@...r.kernel.org
> diff --git a/drivers/power/supply/Kconfig b/drivers/power/supply/Kconfig
> index 92f9f7aae92f249aa165e68dbcd4cebb569286ea..3a2cdb95c98e44324151ac2b86d740ae2923ee77 100644
> --- a/drivers/power/supply/Kconfig
> +++ b/drivers/power/supply/Kconfig
> @@ -631,6 +631,17 @@ config CHARGER_MAX77705
>  	help
>  	  Say Y to enable support for the Maxim MAX77705 battery charger.
>  
> +config CHARGER_MAX77759
> +	tristate "Maxim MAX77759 battery charger driver"
> +	depends on MFD_MAX77759 && REGULATOR
> +	default MFD_MAX77759
> +	help
> +	  Say M or Y here to enable the MAX77759 battery charger. MAX77759
> +	  charger is a function of the MAX77759 PMIC. This is a dual input
> +	  switch-mode charger. This driver supports buck and OTG boost modes.
> +
> +	  If built as a module, it will be called max77759_charger.
> +
>  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 4b79d5abc49a7fd1e37a26d0c89f94d9fe3a916f..6af905875ad5e3b393a7030405355b9a975870f6 100644
> --- a/drivers/power/supply/Makefile
> +++ b/drivers/power/supply/Makefile
> @@ -128,3 +128,4 @@ obj-$(CONFIG_CHARGER_SURFACE)	+= surface_charger.o
>  obj-$(CONFIG_BATTERY_UG3105)	+= ug3105_battery.o
>  obj-$(CONFIG_CHARGER_QCOM_SMB2)	+= qcom_smbx.o
>  obj-$(CONFIG_FUEL_GAUGE_MM8013)	+= mm8013.o
> +obj-$(CONFIG_CHARGER_MAX77759)	+= max77759_charger.o
> diff --git a/drivers/power/supply/max77759_charger.c b/drivers/power/supply/max77759_charger.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..34b5ea0967eb7b4716e81ee1a55227ac872493b0
> --- /dev/null
> +++ b/drivers/power/supply/max77759_charger.c
> @@ -0,0 +1,737 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * max77759_charger.c - Battery charger driver for MAX77759 charger device.
> + *
> + * Copyright 2025 Google LLC.
> + */
> +
> +#include <linux/bitfield.h>
> +#include <linux/cleanup.h>
> +#include <linux/device.h>
> +#include <linux/devm-helpers.h>
> +#include <linux/interrupt.h>
> +#include <linux/irq.h>
> +#include <linux/math64.h>
> +#include <linux/mfd/max77759.h>
> +#include <linux/module.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/mutex.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/power_supply.h>
> +#include <linux/regmap.h>
> +#include <linux/regulator/driver.h>
> +#include <linux/string_choices.h>
> +
> +/* Default values for Fast Charge Current & Float Voltage */
> +#define CHG_CC_DEFAULT_UA			2266770
> +#define CHG_FV_DEFAULT_MV			4300
> +
> +#define FOREACH_IRQ(S)			\
> +	S(AICL),			\
> +	S(CHGIN),			\
> +	S(CHG),				\
> +	S(INLIM),			\
> +	S(BAT_OILO),			\
> +	S(CHG_STA_CC),			\
> +	S(CHG_STA_CV),			\
> +	S(CHG_STA_TO),			\
> +	S(CHG_STA_DONE)
> +
> +#define GENERATE_ENUM(e)		e
> +#define GENERATE_STRING(s)		#s
> +
> +enum {
> +	FOREACH_IRQ(GENERATE_ENUM)
> +};
> +
> +static const char *const chgr_irqs_str[] = {
> +	FOREACH_IRQ(GENERATE_STRING)
> +};
> +
> +#define NUM_IRQS			ARRAY_SIZE(chgr_irqs_str)
> +
> +struct max77759_charger {
> +	struct device *dev;
> +	struct regmap *regmap;
> +	struct power_supply *psy;
> +	struct regulator_dev *chgin_otg_rdev;
> +	struct notifier_block nb;
> +	struct power_supply *tcpm_psy;
> +	struct work_struct psy_work;
> +	int irqs[NUM_IRQS];
> +	struct mutex lock; /* protects the state below */
> +	enum max77759_chgr_mode mode;
> +};
> +
> +static inline int regval_to_val(int reg, int reg_offset, int step, int minval)
> +{
> +	return ((reg - reg_offset) * step) + minval;
> +}
> +
> +static inline int val_to_regval(int val, int minval, int step, int reg_offset)
> +{
> +	s64 dividend;
> +
> +	if (unlikely(step == 0))
> +		return reg_offset;

Does it really make an impact on performance to specify unlikely? Also, I seem to
remember that the if branch is treated as unlikely anyway, but can't find any hard
evidence on that right now.

> +
> +	dividend = (s64)val - minval;
> +	return DIV_S64_ROUND_CLOSEST(dividend, step) + reg_offset;
> +}

For these two functions above, have you considered using the APIs from
include/linux/linear_range.h instead of duplicating in this driver? The
implementations of the above match linear_range_get_value() and
linear_range_get_selector_low() quite nicely.

> +
> +static inline int unlock_prot_regs(struct max77759_charger *chg, bool unlock)
> +{
> +	return regmap_update_bits(chg->regmap, MAX77759_CHGR_REG_CHG_CNFG_06,
> +				  MAX77759_CHGR_REG_CHG_CNFG_06_CHGPROT, unlock
> +				  ? MAX77759_CHGR_REG_CHG_CNFG_06_CHGPROT : 0);
> +}
> +

[...]

> +static irqreturn_t irq_handler(int irq, void *data)
> +{
> +	struct max77759_charger *chg = data;
> +	struct device *dev = chg->dev;
> +	int i;
> +
> +	for (i = 0; i < NUM_IRQS && chg->irqs[i] != irq; i++)
> +		;
> +
> +	if (i == NUM_IRQS) {
> +		dev_err(dev, "Unable to handle irq=%d", irq);
> +		return IRQ_NONE;
> +	} else if (i == BAT_OILO) {
> +		dev_warn(dev, "Battery over-current threshold crossed");
> +	}

Generally, no 'else' is required after return.

> +
> +	power_supply_changed(chg->psy);
> +	return IRQ_HANDLED;
> +}
> +

[...]

> +static void psy_work_item(struct work_struct *work)
> +{
> +	struct max77759_charger *chg =
> +		container_of(work, struct max77759_charger, psy_work);
> +	union power_supply_propval current_limit, online;
> +	int ret;
> +
> +	ret = power_supply_get_property(chg->tcpm_psy,
> +					POWER_SUPPLY_PROP_CURRENT_MAX,
> +					&current_limit);
> +	if (ret) {
> +		dev_err(chg->dev,
> +			"Failed to get CURRENT_MAX psy property, ret=%d",
> +			ret);
> +		return;
> +	}
> +
> +	ret = power_supply_get_property(chg->tcpm_psy, POWER_SUPPLY_PROP_ONLINE,
> +					&online);
> +	if (ret) {
> +		dev_err(chg->dev,
> +			"Failed to get ONLINE psy property, ret=%d",
> +			ret);
> +		return;
> +	}
> +
> +	if (online.intval && current_limit.intval) {
> +		ret = set_input_current_limit(chg, current_limit.intval);
> +		if (ret)
> +			dev_err(chg->dev,
> +				"Unable to set current limit, ret=%d", ret);
> +
> +		charger_set_mode(chg, MAX77759_CHGR_MODE_CHG_BUCK_ON);
> +	} else {
> +		charger_set_mode(chg, MAX77759_CHGR_MODE_OFF);
> +	}

For all the possible errors in this function, should the driver try a bit
harder, even if unlikely to occur? What if the current limit needed to be
reduced, e.g. due to thermal or any other reasons?

Could rescheduling the work be something to consider?

> +}
> +
> +static int psy_changed(struct notifier_block *nb, unsigned long evt, void *data)
> +{
> +	struct max77759_charger *chg = container_of(nb, struct max77759_charger,
> +						    nb);
> +	const char *psy_name = "tcpm-source";

This can be static const char.

> +	struct power_supply *psy = data;
> +
> +	if (!strnstr(psy->desc->name, psy_name, strlen(psy_name)) ||
> +	    evt != PSY_EVENT_PROP_CHANGED)
> +		return NOTIFY_OK;
> +
> +	chg->tcpm_psy = psy;
> +	schedule_work(&chg->psy_work);
> +
> +	return NOTIFY_OK;
> +}
> +
> +static void max_tcpci_unregister_psy_notifier(void *nb)
> +{
> +	power_supply_unreg_notifier(nb);
> +}
> +
> +static int max77759_charger_probe(struct platform_device *pdev)
> +{
> +	struct regulator_config chgin_otg_reg_cfg;
> +	struct power_supply_config psy_cfg;
> +	struct device *dev = &pdev->dev;
> +	struct max77759_charger *chg;
> +	int ret;
> +
> +	device_set_of_node_from_dev(dev, dev->parent);
> +	chg = devm_kzalloc(dev, sizeof(*chg), GFP_KERNEL);
> +	if (!chg)
> +		return -ENOMEM;
> +
> +	platform_set_drvdata(pdev, chg);
> +	chg->dev = dev;
> +	chg->regmap = dev_get_regmap(dev->parent, "charger");
> +	if (!chg->regmap)
> +		return dev_err_probe(dev, -ENODEV, "Missing regmap");
> +
> +	ret = devm_mutex_init(dev, &chg->lock);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to initialize lock");
> +
> +	psy_cfg.fwnode = dev_fwnode(dev);
> +	psy_cfg.drv_data = chg;
> +	chg->psy = devm_power_supply_register(dev, &max77759_charger_desc,
> +					      &psy_cfg);
> +	if (IS_ERR(chg->psy))
> +		return dev_err_probe(dev, -EPROBE_DEFER,
> +				     "Failed to register psy, ret=%ld",
> +				     PTR_ERR(chg->psy));
> +
> +	ret = max77759_charger_init(chg);
> +	if (ret)
> +		return dev_err_probe(dev, ret,
> +				     "Failed to initialize max77759 charger");
> +
> +	chgin_otg_reg_cfg.dev = dev;
> +	chgin_otg_reg_cfg.driver_data = chg;
> +	chgin_otg_reg_cfg.of_node = dev_of_node(dev);
> +	chg->chgin_otg_rdev = devm_regulator_register(dev, &chgin_otg_reg_desc,
> +						      &chgin_otg_reg_cfg);
> +	if (IS_ERR(chg->chgin_otg_rdev))
> +		return dev_err_probe(dev, PTR_ERR(chg->chgin_otg_rdev),
> +				     "Failed to register chgin otg regulator");
> +
> +	ret = devm_work_autocancel(dev, &chg->psy_work, psy_work_item);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to initialize psy work");
> +
> +	chg->nb.notifier_call = psy_changed;
> +	ret = power_supply_reg_notifier(&chg->nb);
> +	if (ret)
> +		return dev_err_probe(dev, ret,
> +				     "Unable to register psy notifier");
> +
> +	ret = devm_add_action_or_reset(dev, max_tcpci_unregister_psy_notifier,
> +				       &chg->nb);
> +	if (ret)
> +		return dev_err_probe(dev, ret,
> +				     "Failed to add devm action to unregister psy notifier");
> +
> +	return max77759_init_irqhandler(chg);
> +}
> +
> +static const struct platform_device_id max77759_charger_id[] = {
> +	{"max77759-charger",},

Minor formatting nit - I believe common practice is to use named initializers:

+	{ .compatible = "max77759-charger", },

> +	{ }
> +};
> +MODULE_DEVICE_TABLE(platform, max77759_charger_id);
> +
> +static struct platform_driver max77759_charger_driver = {
> +	.driver = {
> +		.name = "max77759-charger",

Can it be async, or are there issues with that?

                .probe_type = PROBE_PREFER_ASYNCHRONOUS,


Thanks again Amit!

Cheers,
Andre'

> +	},
> +	.probe = max77759_charger_probe,
> +	.id_table = max77759_charger_id,
> +};
> +module_platform_driver(max77759_charger_driver);
> +
> +MODULE_AUTHOR("Amit Sunil Dhamne <amitsd@...gle.com>");
> +MODULE_DESCRIPTION("Maxim MAX77759 charger driver");
> +MODULE_LICENSE("GPL");

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