xref: /linux/drivers/pwm/pwm-gpio.c (revision 4b132aacb0768ac1e652cf517097ea6f237214b9)
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 
27 struct 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 
41 static 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 
58 static 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 
75 static 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 
101 static 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 
154 static 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 
169 static const struct pwm_ops pwm_gpio_ops = {
170 	.apply = pwm_gpio_apply,
171 	.get_state = pwm_gpio_get_state,
172 };
173 
174 static void pwm_gpio_disable_hrtimer(void *data)
175 {
176 	struct pwm_gpio *gpwm = data;
177 
178 	hrtimer_cancel(&gpwm->gpio_timer);
179 }
180 
181 static 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 
224 static const struct of_device_id pwm_gpio_dt_ids[] = {
225 	{ .compatible = "pwm-gpio" },
226 	{ /* sentinel */ }
227 };
228 MODULE_DEVICE_TABLE(of, pwm_gpio_dt_ids);
229 
230 static 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 };
237 module_platform_driver(pwm_gpio_driver);
238 
239 MODULE_DESCRIPTION("PWM GPIO driver");
240 MODULE_AUTHOR("Vincent Whitchurch");
241 MODULE_LICENSE("GPL");
242