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1// SPDX-License-Identifier: GPL-2.0-or-later2/*3 * The Netronix embedded controller is a microcontroller found in some4 * e-book readers designed by the original design manufacturer Netronix, Inc.5 * It contains RTC, battery monitoring, system power management, and PWM6 * functionality.7 *8 * This driver implements PWM output.9 *10 * Copyright 2020 Jonathan Neuschäfer <j.neuschaefer@gmx.net>11 *12 * Limitations:13 * - The get_state callback is not implemented, because the current state of14 * the PWM output can't be read back from the hardware.15 * - The hardware can only generate normal polarity output.16 * - The period and duty cycle can't be changed together in one atomic action.17 */18 19#include <linux/mfd/ntxec.h>20#include <linux/module.h>21#include <linux/platform_device.h>22#include <linux/pwm.h>23#include <linux/regmap.h>24#include <linux/types.h>25 26struct ntxec_pwm {27 struct ntxec *ec;28};29 30static struct ntxec_pwm *ntxec_pwm_from_chip(struct pwm_chip *chip)31{32 return pwmchip_get_drvdata(chip);33}34 35#define NTXEC_REG_AUTO_OFF_HI 0xa136#define NTXEC_REG_AUTO_OFF_LO 0xa237#define NTXEC_REG_ENABLE 0xa338#define NTXEC_REG_PERIOD_LOW 0xa439#define NTXEC_REG_PERIOD_HIGH 0xa540#define NTXEC_REG_DUTY_LOW 0xa641#define NTXEC_REG_DUTY_HIGH 0xa742 43/*44 * The time base used in the EC is 8MHz, or 125ns. Period and duty cycle are45 * measured in this unit.46 */47#define TIME_BASE_NS 12548 49/*50 * The maximum input value (in nanoseconds) is determined by the time base and51 * the range of the hardware registers that hold the converted value.52 * It fits into 32 bits, so we can do our calculations in 32 bits as well.53 */54#define MAX_PERIOD_NS (TIME_BASE_NS * 0xffff)55 56static int ntxec_pwm_set_raw_period_and_duty_cycle(struct pwm_chip *chip,57 int period, int duty)58{59 struct ntxec_pwm *priv = ntxec_pwm_from_chip(chip);60 61 /*62 * Changes to the period and duty cycle take effect as soon as the63 * corresponding low byte is written, so the hardware may be configured64 * to an inconsistent state after the period is written and before the65 * duty cycle is fully written. If, in such a case, the old duty cycle66 * is longer than the new period, the EC may output 100% for a moment.67 *68 * To minimize the time between the changes to period and duty cycle69 * taking effect, the writes are interleaved.70 */71 72 struct reg_sequence regs[] = {73 { NTXEC_REG_PERIOD_HIGH, ntxec_reg8(period >> 8) },74 { NTXEC_REG_DUTY_HIGH, ntxec_reg8(duty >> 8) },75 { NTXEC_REG_PERIOD_LOW, ntxec_reg8(period) },76 { NTXEC_REG_DUTY_LOW, ntxec_reg8(duty) },77 };78 79 return regmap_multi_reg_write(priv->ec->regmap, regs, ARRAY_SIZE(regs));80}81 82static int ntxec_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm_dev,83 const struct pwm_state *state)84{85 struct ntxec_pwm *priv = ntxec_pwm_from_chip(chip);86 unsigned int period, duty;87 int res;88 89 if (state->polarity != PWM_POLARITY_NORMAL)90 return -EINVAL;91 92 period = min_t(u64, state->period, MAX_PERIOD_NS);93 duty = min_t(u64, state->duty_cycle, period);94 95 period /= TIME_BASE_NS;96 duty /= TIME_BASE_NS;97 98 /*99 * Writing a duty cycle of zero puts the device into a state where100 * writing a higher duty cycle doesn't result in the brightness that it101 * usually results in. This can be fixed by cycling the ENABLE register.102 *103 * As a workaround, write ENABLE=0 when the duty cycle is zero.104 * The case that something has previously set the duty cycle to zero105 * but ENABLE=1, is not handled.106 */107 if (state->enabled && duty != 0) {108 res = ntxec_pwm_set_raw_period_and_duty_cycle(chip, period, duty);109 if (res)110 return res;111 112 res = regmap_write(priv->ec->regmap, NTXEC_REG_ENABLE, ntxec_reg8(1));113 if (res)114 return res;115 116 /* Disable the auto-off timer */117 res = regmap_write(priv->ec->regmap, NTXEC_REG_AUTO_OFF_HI, ntxec_reg8(0xff));118 if (res)119 return res;120 121 return regmap_write(priv->ec->regmap, NTXEC_REG_AUTO_OFF_LO, ntxec_reg8(0xff));122 } else {123 return regmap_write(priv->ec->regmap, NTXEC_REG_ENABLE, ntxec_reg8(0));124 }125}126 127static const struct pwm_ops ntxec_pwm_ops = {128 .apply = ntxec_pwm_apply,129 /*130 * No .get_state callback, because the current state cannot be read131 * back from the hardware.132 */133};134 135static int ntxec_pwm_probe(struct platform_device *pdev)136{137 struct ntxec *ec = dev_get_drvdata(pdev->dev.parent);138 struct ntxec_pwm *priv;139 struct pwm_chip *chip;140 141 device_set_of_node_from_dev(&pdev->dev, pdev->dev.parent);142 143 chip = devm_pwmchip_alloc(&pdev->dev, 1, sizeof(*priv));144 if (IS_ERR(chip))145 return PTR_ERR(chip);146 priv = ntxec_pwm_from_chip(chip);147 148 priv->ec = ec;149 chip->ops = &ntxec_pwm_ops;150 151 return devm_pwmchip_add(&pdev->dev, chip);152}153 154static struct platform_driver ntxec_pwm_driver = {155 .driver = {156 .name = "ntxec-pwm",157 },158 .probe = ntxec_pwm_probe,159};160module_platform_driver(ntxec_pwm_driver);161 162MODULE_AUTHOR("Jonathan Neuschäfer <j.neuschaefer@gmx.net>");163MODULE_DESCRIPTION("PWM driver for Netronix EC");164MODULE_LICENSE("GPL");165MODULE_ALIAS("platform:ntxec-pwm");166