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
pwm_gpio_round(struct pwm_state * dest,const struct pwm_state * src)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
pwm_gpio_toggle(struct pwm_gpio * gpwm,bool level)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
pwm_gpio_timer(struct hrtimer * gpio_timer)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
pwm_gpio_apply(struct pwm_chip * chip,struct pwm_device * pwm,const struct pwm_state * state)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
pwm_gpio_get_state(struct pwm_chip * chip,struct pwm_device * pwm,struct pwm_state * state)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
pwm_gpio_disable_hrtimer(void * data)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
pwm_gpio_probe(struct platform_device * pdev)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