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(desc: gpwm->gpio, value: 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)(l: &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, level: new_level);
94 if (next_toggle)
95 hrtimer_forward(timer: gpio_timer, now: hrtimer_get_expires(timer: gpio_timer),
96 interval: ns_to_ktime(ns: 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(timer: &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(desc: gpwm->gpio, value: invert);
124 if (ret)
125 return ret;
126 }
127
128 guard(spinlock_irqsave)(l: &gpwm->lock);
129
130 if (!state->enabled) {
131 pwm_gpio_round(dest: &gpwm->state, src: state);
132 gpwm->running = false;
133 gpwm->changing = false;
134
135 gpiod_set_value(desc: gpwm->gpio, value: invert);
136 } else if (gpwm->running) {
137 pwm_gpio_round(dest: &gpwm->next_state, src: state);
138 gpwm->changing = true;
139 } else {
140 unsigned long next_toggle;
141
142 pwm_gpio_round(dest: &gpwm->state, src: state);
143 gpwm->changing = false;
144
145 next_toggle = pwm_gpio_toggle(gpwm, level: !!state->duty_cycle);
146 if (next_toggle)
147 hrtimer_start(timer: &gpwm->gpio_timer, tim: next_toggle,
148 mode: 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)(l: &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(timer: &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(parent: dev, npwm: 1, sizeof_priv: sizeof(*gpwm));
189 if (IS_ERR(ptr: chip))
190 return PTR_ERR(ptr: chip);
191
192 gpwm = pwmchip_get_drvdata(chip);
193
194 spin_lock_init(&gpwm->lock);
195
196 gpwm->gpio = devm_gpiod_get(dev, NULL, flags: GPIOD_ASIS);
197 if (IS_ERR(ptr: gpwm->gpio))
198 return dev_err_probe(dev, err: PTR_ERR(ptr: gpwm->gpio),
199 fmt: "%pfw: could not get gpio\n",
200 dev_fwnode(dev));
201
202 if (gpiod_cansleep(desc: gpwm->gpio))
203 return dev_err_probe(dev, err: -EINVAL,
204 fmt: "%pfw: sleeping GPIO not supported\n",
205 dev_fwnode(dev));
206
207 chip->ops = &pwm_gpio_ops;
208 chip->atomic = true;
209
210 hrtimer_setup(timer: &gpwm->gpio_timer, function: pwm_gpio_timer, CLOCK_MONOTONIC, mode: HRTIMER_MODE_REL);
211
212 ret = devm_add_action_or_reset(dev, pwm_gpio_disable_hrtimer, gpwm);
213 if (ret)
214 return ret;
215
216 ret = pwmchip_add(chip);
217 if (ret < 0)
218 return dev_err_probe(dev, err: ret, fmt: "could not add pwmchip\n");
219
220 return 0;
221}
222
223static const struct of_device_id pwm_gpio_dt_ids[] = {
224 { .compatible = "pwm-gpio" },
225 { /* sentinel */ }
226};
227MODULE_DEVICE_TABLE(of, pwm_gpio_dt_ids);
228
229static struct platform_driver pwm_gpio_driver = {
230 .driver = {
231 .name = "pwm-gpio",
232 .of_match_table = pwm_gpio_dt_ids,
233 },
234 .probe = pwm_gpio_probe,
235};
236module_platform_driver(pwm_gpio_driver);
237
238MODULE_DESCRIPTION("PWM GPIO driver");
239MODULE_AUTHOR("Vincent Whitchurch");
240MODULE_LICENSE("GPL");
241

source code of linux/drivers/pwm/pwm-gpio.c