// SPDX-License-Identifier: GPL-2.0-only
/*
 * Generic software PWM for modulating GPIOs
 *
 * Copyright (C) 2020 Axis Communications AB
 * Copyright (C) 2020 Nicola Di Lieto
 * Copyright (C) 2024 Stefan Wahren
 * Copyright (C) 2024 Linus Walleij
 */

#include <linux/cleanup.h>
#include <linux/container_of.h>
#include <linux/device.h>
#include <linux/err.h>
#include <linux/gpio/consumer.h>
#include <linux/hrtimer.h>
#include <linux/math.h>
#include <linux/module.h>
#include <linux/mod_devicetable.h>
#include <linux/platform_device.h>
#include <linux/property.h>
#include <linux/pwm.h>
#include <linux/spinlock.h>
#include <linux/time.h>
#include <linux/types.h>

struct pwm_gpio {
        struct hrtimer gpio_timer;
        struct gpio_desc *gpio;
        struct pwm_state state;
        struct pwm_state next_state;

        /* Protect internal state between pwm_ops and hrtimer */
        spinlock_t lock;

        bool changing;
        bool running;
        bool level;
};

static void pwm_gpio_round(struct pwm_state *dest, const struct pwm_state *src)
{
        u64 dividend;
        u32 remainder;

        *dest = *src;

        /* Round down to hrtimer resolution */
        dividend = dest->period;
        remainder = do_div(dividend, hrtimer_resolution);
        dest->period -= remainder;

        dividend = dest->duty_cycle;
        remainder = do_div(dividend, hrtimer_resolution);
        dest->duty_cycle -= remainder;
}

static u64 pwm_gpio_toggle(struct pwm_gpio *gpwm, bool level)
{
        const struct pwm_state *state = &gpwm->state;
        bool invert = state->polarity == PWM_POLARITY_INVERSED;

        gpwm->level = level;
        gpiod_set_value(gpwm->gpio, gpwm->level ^ invert);

        if (!state->duty_cycle || state->duty_cycle == state->period) {
                gpwm->running = false;
                return 0;
        }

        gpwm->running = true;
        return level ? state->duty_cycle : state->period - state->duty_cycle;
}

static enum hrtimer_restart pwm_gpio_timer(struct hrtimer *gpio_timer)
{
        struct pwm_gpio *gpwm = container_of(gpio_timer, struct pwm_gpio,
                                             gpio_timer);
        u64 next_toggle;
        bool new_level;

        guard(spinlock_irqsave)(&gpwm->lock);

        /* Apply new state at end of current period */
        if (!gpwm->level && gpwm->changing) {
                gpwm->changing = false;
                gpwm->state = gpwm->next_state;
                new_level = !!gpwm->state.duty_cycle;
        } else {
                new_level = !gpwm->level;
        }

        next_toggle = pwm_gpio_toggle(gpwm, new_level);
        if (next_toggle)
                hrtimer_forward(gpio_timer, hrtimer_get_expires(gpio_timer),
                                ns_to_ktime(next_toggle));

        return next_toggle ? HRTIMER_RESTART : HRTIMER_NORESTART;
}

static int pwm_gpio_apply(struct pwm_chip *chip, struct pwm_device *pwm,
                          const struct pwm_state *state)
{
        struct pwm_gpio *gpwm = pwmchip_get_drvdata(chip);
        bool invert = state->polarity == PWM_POLARITY_INVERSED;

        if (state->duty_cycle && state->duty_cycle < hrtimer_resolution)
                return -EINVAL;

        if (state->duty_cycle != state->period &&
            (state->period - state->duty_cycle < hrtimer_resolution))
                return -EINVAL;

        if (!state->enabled) {
                hrtimer_cancel(&gpwm->gpio_timer);
        } else if (!gpwm->running) {
                int ret;

                /*
                 * This just enables the output, but pwm_gpio_toggle()
                 * really starts the duty cycle.
                 */
                ret = gpiod_direction_output(gpwm->gpio, invert);
                if (ret)
                        return ret;
        }

        guard(spinlock_irqsave)(&gpwm->lock);

        if (!state->enabled) {
                pwm_gpio_round(&gpwm->state, state);
                gpwm->running = false;
                gpwm->changing = false;

                gpiod_set_value(gpwm->gpio, invert);
        } else if (gpwm->running) {
                pwm_gpio_round(&gpwm->next_state, state);
                gpwm->changing = true;
        } else {
                unsigned long next_toggle;

                pwm_gpio_round(&gpwm->state, state);
                gpwm->changing = false;

                next_toggle = pwm_gpio_toggle(gpwm, !!state->duty_cycle);
                if (next_toggle)
                        hrtimer_start(&gpwm->gpio_timer, next_toggle,
                                      HRTIMER_MODE_REL);
        }

        return 0;
}

static int pwm_gpio_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
                               struct pwm_state *state)
{
        struct pwm_gpio *gpwm = pwmchip_get_drvdata(chip);

        guard(spinlock_irqsave)(&gpwm->lock);

        if (gpwm->changing)
                *state = gpwm->next_state;
        else
                *state = gpwm->state;

        return 0;
}

static const struct pwm_ops pwm_gpio_ops = {
        .apply = pwm_gpio_apply,
        .get_state = pwm_gpio_get_state,
};

static void pwm_gpio_disable_hrtimer(void *data)
{
        struct pwm_gpio *gpwm = data;

        hrtimer_cancel(&gpwm->gpio_timer);
}

static int pwm_gpio_probe(struct platform_device *pdev)
{
        struct device *dev = &pdev->dev;
        struct pwm_chip *chip;
        struct pwm_gpio *gpwm;
        int ret;

        chip = devm_pwmchip_alloc(dev, 1, sizeof(*gpwm));
        if (IS_ERR(chip))
                return PTR_ERR(chip);

        gpwm = pwmchip_get_drvdata(chip);

        spin_lock_init(&gpwm->lock);

        gpwm->gpio = devm_gpiod_get(dev, NULL, GPIOD_ASIS);
        if (IS_ERR(gpwm->gpio))
                return dev_err_probe(dev, PTR_ERR(gpwm->gpio),
                                     "%pfw: could not get gpio\n",
                                     dev_fwnode(dev));

        if (gpiod_cansleep(gpwm->gpio))
                return dev_err_probe(dev, -EINVAL,
                                     "%pfw: sleeping GPIO not supported\n",
                                     dev_fwnode(dev));

        chip->ops = &pwm_gpio_ops;
        chip->atomic = true;

        hrtimer_setup(&gpwm->gpio_timer, pwm_gpio_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);

        ret = devm_add_action_or_reset(dev, pwm_gpio_disable_hrtimer, gpwm);
        if (ret)
                return ret;

        ret = pwmchip_add(chip);
        if (ret < 0)
                return dev_err_probe(dev, ret, "could not add pwmchip\n");

        return 0;
}

static const struct of_device_id pwm_gpio_dt_ids[] = {
        { .compatible = "pwm-gpio" },
        { /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, pwm_gpio_dt_ids);

static struct platform_driver pwm_gpio_driver = {
        .driver = {
                .name = "pwm-gpio",
                .of_match_table = pwm_gpio_dt_ids,
        },
        .probe = pwm_gpio_probe,
};
module_platform_driver(pwm_gpio_driver);

MODULE_DESCRIPTION("PWM GPIO driver");
MODULE_AUTHOR("Vincent Whitchurch");
MODULE_LICENSE("GPL");