blob: ab63b081df531d66e7b43baf08e850b197276b18 [file] [log] [blame]
// 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 PWM output.
* Copyright 2020 Jonathan Neuschäfer <>
* Limitations:
* - The get_state callback is not implemented, because the current state of
* the PWM output can't be read back from the hardware.
* - The hardware can only generate normal polarity output.
* - The period and duty cycle can't be changed together in one atomic action.
#include <linux/mfd/ntxec.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/pwm.h>
#include <linux/regmap.h>
#include <linux/types.h>
struct ntxec_pwm {
struct device *dev;
struct ntxec *ec;
struct pwm_chip chip;
static struct ntxec_pwm *ntxec_pwm_from_chip(struct pwm_chip *chip)
return container_of(chip, struct ntxec_pwm, chip);
#define NTXEC_REG_AUTO_OFF_HI 0xa1
#define NTXEC_REG_AUTO_OFF_LO 0xa2
#define NTXEC_REG_ENABLE 0xa3
#define NTXEC_REG_DUTY_LOW 0xa6
#define NTXEC_REG_DUTY_HIGH 0xa7
* The time base used in the EC is 8MHz, or 125ns. Period and duty cycle are
* measured in this unit.
#define TIME_BASE_NS 125
* The maximum input value (in nanoseconds) is determined by the time base and
* the range of the hardware registers that hold the converted value.
* It fits into 32 bits, so we can do our calculations in 32 bits as well.
#define MAX_PERIOD_NS (TIME_BASE_NS * 0xffff)
static int ntxec_pwm_set_raw_period_and_duty_cycle(struct pwm_chip *chip,
int period, int duty)
struct ntxec_pwm *priv = ntxec_pwm_from_chip(chip);
* Changes to the period and duty cycle take effect as soon as the
* corresponding low byte is written, so the hardware may be configured
* to an inconsistent state after the period is written and before the
* duty cycle is fully written. If, in such a case, the old duty cycle
* is longer than the new period, the EC may output 100% for a moment.
* To minimize the time between the changes to period and duty cycle
* taking effect, the writes are interleaved.
struct reg_sequence regs[] = {
{ NTXEC_REG_PERIOD_HIGH, ntxec_reg8(period >> 8) },
{ NTXEC_REG_DUTY_HIGH, ntxec_reg8(duty >> 8) },
{ NTXEC_REG_PERIOD_LOW, ntxec_reg8(period) },
{ NTXEC_REG_DUTY_LOW, ntxec_reg8(duty) },
return regmap_multi_reg_write(priv->ec->regmap, regs, ARRAY_SIZE(regs));
static int ntxec_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm_dev,
const struct pwm_state *state)
struct ntxec_pwm *priv = ntxec_pwm_from_chip(chip);
unsigned int period, duty;
int res;
if (state->polarity != PWM_POLARITY_NORMAL)
return -EINVAL;
period = min_t(u64, state->period, MAX_PERIOD_NS);
duty = min_t(u64, state->duty_cycle, period);
period /= TIME_BASE_NS;
duty /= TIME_BASE_NS;
* Writing a duty cycle of zero puts the device into a state where
* writing a higher duty cycle doesn't result in the brightness that it
* usually results in. This can be fixed by cycling the ENABLE register.
* As a workaround, write ENABLE=0 when the duty cycle is zero.
* The case that something has previously set the duty cycle to zero
* but ENABLE=1, is not handled.
if (state->enabled && duty != 0) {
res = ntxec_pwm_set_raw_period_and_duty_cycle(chip, period, duty);
if (res)
return res;
res = regmap_write(priv->ec->regmap, NTXEC_REG_ENABLE, ntxec_reg8(1));
if (res)
return res;
/* Disable the auto-off timer */
res = regmap_write(priv->ec->regmap, NTXEC_REG_AUTO_OFF_HI, ntxec_reg8(0xff));
if (res)
return res;
return regmap_write(priv->ec->regmap, NTXEC_REG_AUTO_OFF_LO, ntxec_reg8(0xff));
} else {
return regmap_write(priv->ec->regmap, NTXEC_REG_ENABLE, ntxec_reg8(0));
static const struct pwm_ops ntxec_pwm_ops = {
.owner = THIS_MODULE,
.apply = ntxec_pwm_apply,
* No .get_state callback, because the current state cannot be read
* back from the hardware.
static int ntxec_pwm_probe(struct platform_device *pdev)
struct ntxec *ec = dev_get_drvdata(pdev->dev.parent);
struct ntxec_pwm *priv;
struct pwm_chip *chip;
pdev->dev.of_node = pdev->dev.parent->of_node;
priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
if (!priv)
return -ENOMEM;
priv->ec = ec;
priv->dev = &pdev->dev;
chip = &priv->chip;
chip->dev = &pdev->dev;
chip->ops = &ntxec_pwm_ops;
chip->npwm = 1;
return devm_pwmchip_add(&pdev->dev, chip);
static struct platform_driver ntxec_pwm_driver = {
.driver = {
.name = "ntxec-pwm",
.probe = ntxec_pwm_probe,
MODULE_AUTHOR("Jonathan Neuschäfer <>");
MODULE_DESCRIPTION("PWM driver for Netronix EC");