pwm-ntxec.c (5076B)
1// SPDX-License-Identifier: GPL-2.0-or-later 2/* 3 * The Netronix embedded controller is a microcontroller found in some 4 * e-book readers designed by the original design manufacturer Netronix, Inc. 5 * It contains RTC, battery monitoring, system power management, and PWM 6 * 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 of 14 * 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 device *dev; 28 struct ntxec *ec; 29 struct pwm_chip chip; 30}; 31 32static struct ntxec_pwm *ntxec_pwm_from_chip(struct pwm_chip *chip) 33{ 34 return container_of(chip, struct ntxec_pwm, chip); 35} 36 37#define NTXEC_REG_AUTO_OFF_HI 0xa1 38#define NTXEC_REG_AUTO_OFF_LO 0xa2 39#define NTXEC_REG_ENABLE 0xa3 40#define NTXEC_REG_PERIOD_LOW 0xa4 41#define NTXEC_REG_PERIOD_HIGH 0xa5 42#define NTXEC_REG_DUTY_LOW 0xa6 43#define NTXEC_REG_DUTY_HIGH 0xa7 44 45/* 46 * The time base used in the EC is 8MHz, or 125ns. Period and duty cycle are 47 * measured in this unit. 48 */ 49#define TIME_BASE_NS 125 50 51/* 52 * The maximum input value (in nanoseconds) is determined by the time base and 53 * the range of the hardware registers that hold the converted value. 54 * It fits into 32 bits, so we can do our calculations in 32 bits as well. 55 */ 56#define MAX_PERIOD_NS (TIME_BASE_NS * 0xffff) 57 58static int ntxec_pwm_set_raw_period_and_duty_cycle(struct pwm_chip *chip, 59 int period, int duty) 60{ 61 struct ntxec_pwm *priv = ntxec_pwm_from_chip(chip); 62 63 /* 64 * Changes to the period and duty cycle take effect as soon as the 65 * corresponding low byte is written, so the hardware may be configured 66 * to an inconsistent state after the period is written and before the 67 * duty cycle is fully written. If, in such a case, the old duty cycle 68 * is longer than the new period, the EC may output 100% for a moment. 69 * 70 * To minimize the time between the changes to period and duty cycle 71 * taking effect, the writes are interleaved. 72 */ 73 74 struct reg_sequence regs[] = { 75 { NTXEC_REG_PERIOD_HIGH, ntxec_reg8(period >> 8) }, 76 { NTXEC_REG_DUTY_HIGH, ntxec_reg8(duty >> 8) }, 77 { NTXEC_REG_PERIOD_LOW, ntxec_reg8(period) }, 78 { NTXEC_REG_DUTY_LOW, ntxec_reg8(duty) }, 79 }; 80 81 return regmap_multi_reg_write(priv->ec->regmap, regs, ARRAY_SIZE(regs)); 82} 83 84static int ntxec_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm_dev, 85 const struct pwm_state *state) 86{ 87 struct ntxec_pwm *priv = ntxec_pwm_from_chip(chip); 88 unsigned int period, duty; 89 int res; 90 91 if (state->polarity != PWM_POLARITY_NORMAL) 92 return -EINVAL; 93 94 period = min_t(u64, state->period, MAX_PERIOD_NS); 95 duty = min_t(u64, state->duty_cycle, period); 96 97 period /= TIME_BASE_NS; 98 duty /= TIME_BASE_NS; 99 100 /* 101 * Writing a duty cycle of zero puts the device into a state where 102 * writing a higher duty cycle doesn't result in the brightness that it 103 * usually results in. This can be fixed by cycling the ENABLE register. 104 * 105 * As a workaround, write ENABLE=0 when the duty cycle is zero. 106 * The case that something has previously set the duty cycle to zero 107 * but ENABLE=1, is not handled. 108 */ 109 if (state->enabled && duty != 0) { 110 res = ntxec_pwm_set_raw_period_and_duty_cycle(chip, period, duty); 111 if (res) 112 return res; 113 114 res = regmap_write(priv->ec->regmap, NTXEC_REG_ENABLE, ntxec_reg8(1)); 115 if (res) 116 return res; 117 118 /* Disable the auto-off timer */ 119 res = regmap_write(priv->ec->regmap, NTXEC_REG_AUTO_OFF_HI, ntxec_reg8(0xff)); 120 if (res) 121 return res; 122 123 return regmap_write(priv->ec->regmap, NTXEC_REG_AUTO_OFF_LO, ntxec_reg8(0xff)); 124 } else { 125 return regmap_write(priv->ec->regmap, NTXEC_REG_ENABLE, ntxec_reg8(0)); 126 } 127} 128 129static const struct pwm_ops ntxec_pwm_ops = { 130 .owner = THIS_MODULE, 131 .apply = ntxec_pwm_apply, 132 /* 133 * No .get_state callback, because the current state cannot be read 134 * back from the hardware. 135 */ 136}; 137 138static int ntxec_pwm_probe(struct platform_device *pdev) 139{ 140 struct ntxec *ec = dev_get_drvdata(pdev->dev.parent); 141 struct ntxec_pwm *priv; 142 struct pwm_chip *chip; 143 144 pdev->dev.of_node = pdev->dev.parent->of_node; 145 146 priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL); 147 if (!priv) 148 return -ENOMEM; 149 150 priv->ec = ec; 151 priv->dev = &pdev->dev; 152 153 chip = &priv->chip; 154 chip->dev = &pdev->dev; 155 chip->ops = &ntxec_pwm_ops; 156 chip->npwm = 1; 157 158 return devm_pwmchip_add(&pdev->dev, chip); 159} 160 161static struct platform_driver ntxec_pwm_driver = { 162 .driver = { 163 .name = "ntxec-pwm", 164 }, 165 .probe = ntxec_pwm_probe, 166}; 167module_platform_driver(ntxec_pwm_driver); 168 169MODULE_AUTHOR("Jonathan Neuschäfer <j.neuschaefer@gmx.net>"); 170MODULE_DESCRIPTION("PWM driver for Netronix EC"); 171MODULE_LICENSE("GPL"); 172MODULE_ALIAS("platform:ntxec-pwm");