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Message-ID: <aWblrimQTy5-khZF@venus>
Date: Wed, 14 Jan 2026 01:55:47 +0100
From: Sebastian Reichel <sebastian.reichel@...labora.com>
To: Josua Mayer <josua.mayer@....eu>
Cc: Jonathan Neuschäfer <j.neuschaefer@....net>,
Lee Jones <lee@...nel.org>, Rob Herring <robh@...nel.org>,
Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>,
Shawn Guo <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>,
Pengutronix Kernel Team <kernel@...gutronix.de>, Fabio Estevam <festevam@...il.com>, linux-kernel@...r.kernel.org,
linux-pm@...r.kernel.org, devicetree@...r.kernel.org, imx@...ts.linux.dev,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 3/4] power: supply: add battery driver for netronix ec
Hi,
On Fri, Jan 02, 2026 at 07:00:32PM +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@....eu>
> ---
> drivers/power/supply/Kconfig | 9 ++++
> drivers/power/supply/Makefile | 1 +
> drivers/power/supply/ntxec-battery.c | 101 +++++++++++++++++++++++++++++++++++
That's indeed simple :)
> 3 files changed, 111 insertions(+)
>
> diff --git a/drivers/power/supply/Kconfig b/drivers/power/supply/Kconfig
> index 92f9f7aae92f..0f944c10e50b 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
You can add "|| COMPILE_TEST"
> + 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 device-tree if available.
> +
> endif # POWER_SUPPLY
> diff --git a/drivers/power/supply/Makefile b/drivers/power/supply/Makefile
> index 4b79d5abc49a..db6fc815f9da 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 000000000000..f49f0966d18d
> --- /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@....eu>
> + */
> +
> +#include <linux/mfd/ntxec.h>
^ you probably don't need this with my comments down below :)
> +#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;
> +};
Store the regmap instead of the ec. You don't need anything else.
> +#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.
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);
Based on the regmap comment above, I think you can just do the
following and completley avoid 'struct ntxec' (please test):
struct regmap *regmap = dev_get_regmap(dev->parent, NULL);
> + 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@....eu>");
> +MODULE_DESCRIPTION("Battery driver for Netronix EC");
> +MODULE_LICENSE("GPL");
> +MODULE_ALIAS("platform:ntxec-battery");
I know there are a bunch of wrong examples in my subsystem, but the
proper way to do this is to drop this alias and instead add a
platform_device_id table together with MODULE_DEVICE_TABLE(platform, ...).
See for example cros_peripheral_charger.c
Greetings,
-- Sebastian
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