1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * Generic software PWM for modulating GPIOs
  4 *
  5 * Copyright (C) 2020 Axis Communications AB
  6 * Copyright (C) 2020 Nicola Di Lieto
  7 * Copyright (C) 2024 Stefan Wahren
  8 * Copyright (C) 2024 Linus Walleij
  9 */
 10
 11#include <linux/cleanup.h>
 12#include <linux/container_of.h>
 13#include <linux/device.h>
 14#include <linux/err.h>
 15#include <linux/gpio/consumer.h>
 16#include <linux/hrtimer.h>
 17#include <linux/math.h>
 18#include <linux/module.h>
 19#include <linux/mod_devicetable.h>
 20#include <linux/platform_device.h>
 21#include <linux/property.h>
 22#include <linux/pwm.h>
 23#include <linux/spinlock.h>
 24#include <linux/time.h>
 25#include <linux/types.h>
 26
 27struct pwm_gpio {
 28	struct hrtimer gpio_timer;
 29	struct gpio_desc *gpio;
 30	struct pwm_state state;
 31	struct pwm_state next_state;
 32
 33	/* Protect internal state between pwm_ops and hrtimer */
 34	spinlock_t lock;
 35
 36	bool changing;
 37	bool running;
 38	bool level;
 39};
 40
 41static void pwm_gpio_round(struct pwm_state *dest, const struct pwm_state *src)
 42{
 43	u64 dividend;
 44	u32 remainder;
 45
 46	*dest = *src;
 47
 48	/* Round down to hrtimer resolution */
 49	dividend = dest->period;
 50	remainder = do_div(dividend, hrtimer_resolution);
 51	dest->period -= remainder;
 52
 53	dividend = dest->duty_cycle;
 54	remainder = do_div(dividend, hrtimer_resolution);
 55	dest->duty_cycle -= remainder;
 56}
 57
 58static u64 pwm_gpio_toggle(struct pwm_gpio *gpwm, bool level)
 59{
 60	const struct pwm_state *state = &gpwm->state;
 61	bool invert = state->polarity == PWM_POLARITY_INVERSED;
 62
 63	gpwm->level = level;
 64	gpiod_set_value(gpwm->gpio, gpwm->level ^ invert);
 65
 66	if (!state->duty_cycle || state->duty_cycle == state->period) {
 67		gpwm->running = false;
 68		return 0;
 69	}
 70
 71	gpwm->running = true;
 72	return level ? state->duty_cycle : state->period - state->duty_cycle;
 73}
 74
 75static enum hrtimer_restart pwm_gpio_timer(struct hrtimer *gpio_timer)
 76{
 77	struct pwm_gpio *gpwm = container_of(gpio_timer, struct pwm_gpio,
 78					     gpio_timer);
 79	u64 next_toggle;
 80	bool new_level;
 81
 82	guard(spinlock_irqsave)(&gpwm->lock);
 83
 84	/* Apply new state at end of current period */
 85	if (!gpwm->level && gpwm->changing) {
 86		gpwm->changing = false;
 87		gpwm->state = gpwm->next_state;
 88		new_level = !!gpwm->state.duty_cycle;
 89	} else {
 90		new_level = !gpwm->level;
 91	}
 92
 93	next_toggle = pwm_gpio_toggle(gpwm, new_level);
 94	if (next_toggle)
 95		hrtimer_forward(gpio_timer, hrtimer_get_expires(gpio_timer),
 96				ns_to_ktime(next_toggle));
 97
 98	return next_toggle ? HRTIMER_RESTART : HRTIMER_NORESTART;
 99}
100
101static int pwm_gpio_apply(struct pwm_chip *chip, struct pwm_device *pwm,
102			  const struct pwm_state *state)
103{
104	struct pwm_gpio *gpwm = pwmchip_get_drvdata(chip);
105	bool invert = state->polarity == PWM_POLARITY_INVERSED;
106
107	if (state->duty_cycle && state->duty_cycle < hrtimer_resolution)
108		return -EINVAL;
109
110	if (state->duty_cycle != state->period &&
111	    (state->period - state->duty_cycle < hrtimer_resolution))
112		return -EINVAL;
113
114	if (!state->enabled) {
115		hrtimer_cancel(&gpwm->gpio_timer);
116	} else if (!gpwm->running) {
117		int ret;
118
119		/*
120		 * This just enables the output, but pwm_gpio_toggle()
121		 * really starts the duty cycle.
122		 */
123		ret = gpiod_direction_output(gpwm->gpio, invert);
124		if (ret)
125			return ret;
126	}
127
128	guard(spinlock_irqsave)(&gpwm->lock);
129
130	if (!state->enabled) {
131		pwm_gpio_round(&gpwm->state, state);
132		gpwm->running = false;
133		gpwm->changing = false;
134
135		gpiod_set_value(gpwm->gpio, invert);
136	} else if (gpwm->running) {
137		pwm_gpio_round(&gpwm->next_state, state);
138		gpwm->changing = true;
139	} else {
140		unsigned long next_toggle;
141
142		pwm_gpio_round(&gpwm->state, state);
143		gpwm->changing = false;
144
145		next_toggle = pwm_gpio_toggle(gpwm, !!state->duty_cycle);
146		if (next_toggle)
147			hrtimer_start(&gpwm->gpio_timer, next_toggle,
148				      HRTIMER_MODE_REL);
149	}
150
151	return 0;
152}
153
154static int pwm_gpio_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
155			       struct pwm_state *state)
156{
157	struct pwm_gpio *gpwm = pwmchip_get_drvdata(chip);
158
159	guard(spinlock_irqsave)(&gpwm->lock);
160
161	if (gpwm->changing)
162		*state = gpwm->next_state;
163	else
164		*state = gpwm->state;
165
166	return 0;
167}
168
169static const struct pwm_ops pwm_gpio_ops = {
170	.apply = pwm_gpio_apply,
171	.get_state = pwm_gpio_get_state,
172};
173
174static void pwm_gpio_disable_hrtimer(void *data)
175{
176	struct pwm_gpio *gpwm = data;
177
178	hrtimer_cancel(&gpwm->gpio_timer);
179}
180
181static int pwm_gpio_probe(struct platform_device *pdev)
182{
183	struct device *dev = &pdev->dev;
184	struct pwm_chip *chip;
185	struct pwm_gpio *gpwm;
186	int ret;
187
188	chip = devm_pwmchip_alloc(dev, 1, sizeof(*gpwm));
189	if (IS_ERR(chip))
190		return PTR_ERR(chip);
191
192	gpwm = pwmchip_get_drvdata(chip);
193
194	spin_lock_init(&gpwm->lock);
195
196	gpwm->gpio = devm_gpiod_get(dev, NULL, GPIOD_ASIS);
197	if (IS_ERR(gpwm->gpio))
198		return dev_err_probe(dev, PTR_ERR(gpwm->gpio),
199				     "%pfw: could not get gpio\n",
200				     dev_fwnode(dev));
201
202	if (gpiod_cansleep(gpwm->gpio))
203		return dev_err_probe(dev, -EINVAL,
204				     "%pfw: sleeping GPIO not supported\n",
205				     dev_fwnode(dev));
206
207	chip->ops = &pwm_gpio_ops;
208	chip->atomic = true;
209
210	hrtimer_init(&gpwm->gpio_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
211	ret = devm_add_action_or_reset(dev, pwm_gpio_disable_hrtimer, gpwm);
212	if (ret)
213		return ret;
214
215	gpwm->gpio_timer.function = pwm_gpio_timer;
216
217	ret = pwmchip_add(chip);
218	if (ret < 0)
219		return dev_err_probe(dev, ret, "could not add pwmchip\n");
220
221	return 0;
222}
223
224static const struct of_device_id pwm_gpio_dt_ids[] = {
225	{ .compatible = "pwm-gpio" },
226	{ /* sentinel */ }
227};
228MODULE_DEVICE_TABLE(of, pwm_gpio_dt_ids);
229
230static struct platform_driver pwm_gpio_driver = {
231	.driver = {
232		.name = "pwm-gpio",
233		.of_match_table = pwm_gpio_dt_ids,
234	},
235	.probe = pwm_gpio_probe,
236};
237module_platform_driver(pwm_gpio_driver);
238
239MODULE_DESCRIPTION("PWM GPIO driver");
240MODULE_AUTHOR("Vincent Whitchurch");
241MODULE_LICENSE("GPL");