Re: [PATCH 1/3] power: supply: add battery driver for netronix ec

Ing. Josua Mayer
2025-12-29T11:10:28Z

Am 28.12.25 um 18:56 schrieb J. Neuschäfer:
> Hello!
>
> Nice to see someone work on the Netronix EC :-)
>
> On Sat, Dec 27, 2025 at 05:28:13PM +0100, Josua Mayer wrote:
>> Implement a simple battery driver for monitoring voltage with the
>> netronix embedded controller found in certain ebook readers.
>>
>> Signed-off-by: Josua Mayer <josua.mayer@jm0.eu>
>> ---
>> drivers/mfd/ntxec.c | 1 +
>> drivers/power/supply/Kconfig | 9 ++++
>> drivers/power/supply/Makefile | 1 +
>> drivers/power/supply/ntxec-battery.c | 101 +++++++++++++++++++++++++++++++++++
>> 4 files changed, 112 insertions(+)
>>
>> diff --git a/drivers/mfd/ntxec.c b/drivers/mfd/ntxec.c
>> index 08c68de0f01bc..d5059b8862aa8 100644
>> --- a/drivers/mfd/ntxec.c
>> +++ b/drivers/mfd/ntxec.c
>> @@ -139,6 +139,7 @@ static const struct regmap_config regmap_config = {
>> static const struct mfd_cell ntxec_subdev[] = {
>> { .name = "ntxec-rtc" },
>> { .name = "ntxec-pwm" },
>> + { .name = "ntxec-battery" },
>> };
>>
>> static const struct mfd_cell ntxec_subdev_pwm[] = {
>> diff --git a/drivers/power/supply/Kconfig b/drivers/power/supply/Kconfig
>> index 92f9f7aae92f2..5674a23ba7bd6 100644
>> --- a/drivers/power/supply/Kconfig
>> +++ b/drivers/power/supply/Kconfig
>> @@ -1132,4 +1132,13 @@ config FUEL_GAUGE_MM8013
>> the state of charge, temperature, cycle count, actual and design
>> capacity, etc.
>>
>> +config BATTERY_NTXEC
>> + tristate "Battery driver for Netronix embedded controller"
>> + depends on MFD_NTXEC
>> + help
>> + Say yes here to enable netronix ec battery monitoring driver.
>> + It enables the monitoring battery voltage on certain e-book readers
>> + using an embedded controller by ODM Netronix. Battery design
>> + characteristics are read from Firmware Tables if available.
>
> What do you mean by Firmware Tables, and where does this happen?
Effectively I mean device-tree.

This happens in power-supply core automatically for type battery:

static struct power_supply *__must_check
__power_supply_register(struct device *parent,
const struct power_supply_desc *desc,
const struct power_supply_config *cfg)
{
...
/*
* Expose constant battery info, if it is available. While there are
* some chargers accessing constant battery data, we only want to
* expose battery data to userspace for battery devices.
*/
if (desc->type == POWER_SUPPLY_TYPE_BATTERY) {
rc = power_supply_get_battery_info(psy, &psy->battery_info);
if (rc && rc != -ENODEV && rc != -ENOENT)
goto check_supplies_failed;
}
...
}

This code particular is the reason I marked it optional in DT binding.

>
> (I guess it means devicetree/fwnode, but "git grep -i 'firmware tables'"
Yes, given that power_supply_get_battery_info uses fwnode_* functions.

> doesn't show many uses of that term)
I was struggling with the phrasing - can change to something better.

>
>> +
>> endif # POWER_SUPPLY
>> diff --git a/drivers/power/supply/Makefile b/drivers/power/supply/Makefile
>> index 4b79d5abc49a7..db6fc815f9da2 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_BATTERY_NTXEC) += ntxec-battery.o
>> diff --git a/drivers/power/supply/ntxec-battery.c b/drivers/power/supply/ntxec-battery.c
>> new file mode 100644
>> index 0000000000000..f49f0966d18dd
>> --- /dev/null
>> +++ b/drivers/power/supply/ntxec-battery.c
>> @@ -0,0 +1,101 @@
>> +// SPDX-License-Identifier: GPL-2.0-or-later
>> +/*
>> + * The Netronix embedded controller is a microcontroller found in some
>> + * e-book readers designed by the original design manufacturer Netronix, Inc.
>> + * It contains RTC, battery monitoring, system power management, and PWM
>> + * functionality.
>> + *
>> + * This driver implements battery monitoring.
>> + *
>> + * Copyright 2021 Josua Mayer <josua.mayer@jm0.eu>
>> + */
>> +
>> +#include <linux/mfd/ntxec.h>
>> +#include <linux/module.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/power_supply.h>
>> +#include <linux/property.h>
>> +#include <linux/regmap.h>
>> +
>> +static const enum power_supply_property ntxec_battery_properties[] = {
>> + POWER_SUPPLY_PROP_VOLTAGE_NOW,
>> +};
>> +
>> +struct ntxec_battery {
>> + struct ntxec *ec;
>> +};
>> +
>> +#define NTXEC_REG_READ_BATTERY 0x41
>> +
>> +static int ntxec_battery_get_property(struct power_supply *psy,
>> + enum power_supply_property psp,
>> + union power_supply_propval *val)
>> +{
>> + struct ntxec_battery *priv = power_supply_get_drvdata(psy);
>> + int ret;
>> + unsigned int value;
>> +
>> + switch (psp) {
>> + case POWER_SUPPLY_PROP_VOLTAGE_NOW:
>> + ret = regmap_read(priv->ec->regmap, NTXEC_REG_READ_BATTERY, &value);
>> + if (ret < 0)
>> + return ret;
>> +
>> + /* ec value to microvolt conversion:
>> + * vendor kernel source suggests linear behaviour from 3V to 4.2V
>> + * with readings 767 to 1023; each increment represents 4687,5uV.
>> + * adjust 3V boundary slightly to report exactly 4.2V when full.
>> + */
>> + val->intval = 2999872 + (value - 767) * 4688;
>> + break;
>> + default:
>> + dev_err(&psy->dev, "%s: invalid property %u\n", __func__, psp);
>> + return -EINVAL;
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static const struct power_supply_desc ntxec_battery_desc = {
>> + .name = "ec-battery",
>> + .type = POWER_SUPPLY_TYPE_BATTERY,
>> + .properties = ntxec_battery_properties,
>> + .get_property = ntxec_battery_get_property,
>> + .num_properties = ARRAY_SIZE(ntxec_battery_properties),
>> +};
>> +
>> +static int ntxec_battery_probe(struct platform_device *pdev)
>> +{
>> + struct device *dev = &pdev->dev;
>> + struct ntxec *ec = dev_get_drvdata(dev->parent);
>> + struct power_supply_config psy_cfg = {};
>> + struct ntxec_battery *priv;
>> + struct power_supply *psy;
>> +
>> + priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
>> + if (!priv)
>> + return -ENOMEM;
>> +
>> + priv->ec = ec;
>> + psy_cfg.drv_data = priv;
>> + psy_cfg.fwnode = dev_fwnode(dev->parent);
>> + psy_cfg.no_wakeup_source = true;
>> + psy = devm_power_supply_register(dev, &ntxec_battery_desc, &psy_cfg);
>> + if (IS_ERR(psy))
>> + return PTR_ERR(psy);
>> +
>> + return 0;
>> +}
>> +
>> +static struct platform_driver ntxec_battery_driver = {
>> + .driver = {
>> + .name = "ntxec-battery",
>> + },
>> + .probe = ntxec_battery_probe,
>> +};
>> +module_platform_driver(ntxec_battery_driver);
>> +
>> +MODULE_AUTHOR("Josua Mayer <josua.mayer@jm0.eu>");
>> +MODULE_DESCRIPTION("Battery driver for Netronix EC");
>> +MODULE_LICENSE("GPL");
>> +MODULE_ALIAS("platform:ntxec-battery");
>
> Thanks,
> J. Neuschäfer