// SPDX-License-Identifier: GPL-2.0+
/*
 * Azoteq IQS620A PWM Generator
 *
 * Copyright (C) 2019 Jeff LaBundy <jeff@labundy.com>
 *
 * Limitations:
 * - The period is fixed to 1 ms and is generated continuously despite changes
 *   to the duty cycle or enable/disable state.
 * - Changes to the duty cycle or enable/disable state take effect immediately
 *   and may result in a glitch during the period in which the change is made.
 * - The device cannot generate a 0% duty cycle. For duty cycles below 1 / 256
 *   ms, the output is disabled and relies upon an external pull-down resistor
 *   to hold the GPIO3/LTX pin low.
 */

#include <linux/device.h>
#include <linux/kernel.h>
#include <linux/mfd/iqs62x.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/notifier.h>
#include <linux/platform_device.h>
#include <linux/pwm.h>
#include <linux/regmap.h>
#include <linux/slab.h>

#define IQS620_PWR_SETTINGS                     0xd2
#define IQS620_PWR_SETTINGS_PWM_OUT             BIT(7)

#define IQS620_PWM_DUTY_CYCLE                   0xd8

#define IQS620_PWM_PERIOD_NS                    1000000

struct iqs620_pwm_private {
        struct iqs62x_core *iqs62x;
        struct device *dev;
        struct notifier_block notifier;
        struct mutex lock;
        unsigned int duty_scale;
};

static inline struct iqs620_pwm_private *iqs620_pwm_from_chip(struct pwm_chip *chip)
{
        return pwmchip_get_drvdata(chip);
}

static int iqs620_pwm_init(struct iqs620_pwm_private *iqs620_pwm,
                           unsigned int duty_scale)
{
        struct iqs62x_core *iqs62x = iqs620_pwm->iqs62x;
        int ret;

        if (!duty_scale)
                return regmap_clear_bits(iqs62x->regmap, IQS620_PWR_SETTINGS,
                                         IQS620_PWR_SETTINGS_PWM_OUT);

        ret = regmap_write(iqs62x->regmap, IQS620_PWM_DUTY_CYCLE,
                           duty_scale - 1);
        if (ret)
                return ret;

        return regmap_set_bits(iqs62x->regmap, IQS620_PWR_SETTINGS,
                               IQS620_PWR_SETTINGS_PWM_OUT);
}

static int iqs620_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
                            const struct pwm_state *state)
{
        struct iqs620_pwm_private *iqs620_pwm;
        unsigned int duty_cycle;
        unsigned int duty_scale;
        int ret;

        if (state->polarity != PWM_POLARITY_NORMAL)
                return -EINVAL;

        if (state->period < IQS620_PWM_PERIOD_NS)
                return -EINVAL;

        iqs620_pwm = iqs620_pwm_from_chip(chip);

        /*
         * The duty cycle generated by the device is calculated as follows:
         *
         * duty_cycle = (IQS620_PWM_DUTY_CYCLE + 1) / 256 * 1 ms
         *
         * ...where IQS620_PWM_DUTY_CYCLE is a register value between 0 and 255
         * (inclusive). Therefore the lowest duty cycle the device can generate
         * while the output is enabled is 1 / 256 ms.
         *
         * For lower duty cycles (e.g. 0), the PWM output is simply disabled to
         * allow an external pull-down resistor to hold the GPIO3/LTX pin low.
         */
        duty_cycle = min_t(u64, state->duty_cycle, IQS620_PWM_PERIOD_NS);
        duty_scale = duty_cycle * 256 / IQS620_PWM_PERIOD_NS;

        if (!state->enabled)
                duty_scale = 0;

        mutex_lock(&iqs620_pwm->lock);

        ret = iqs620_pwm_init(iqs620_pwm, duty_scale);
        if (!ret)
                iqs620_pwm->duty_scale = duty_scale;

        mutex_unlock(&iqs620_pwm->lock);

        return ret;
}

static int iqs620_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
                                struct pwm_state *state)
{
        struct iqs620_pwm_private *iqs620_pwm;

        iqs620_pwm = iqs620_pwm_from_chip(chip);

        mutex_lock(&iqs620_pwm->lock);

        /*
         * Since the device cannot generate a 0% duty cycle, requests to do so
         * cause subsequent calls to iqs620_pwm_get_state to report the output
         * as disabled. This is not ideal, but is the best compromise based on
         * the capabilities of the device.
         */
        state->enabled = iqs620_pwm->duty_scale > 0;
        state->duty_cycle = DIV_ROUND_UP(iqs620_pwm->duty_scale *
                                         IQS620_PWM_PERIOD_NS, 256);

        mutex_unlock(&iqs620_pwm->lock);

        state->period = IQS620_PWM_PERIOD_NS;
        state->polarity = PWM_POLARITY_NORMAL;

        return 0;
}

static int iqs620_pwm_notifier(struct notifier_block *notifier,
                               unsigned long event_flags, void *context)
{
        struct iqs620_pwm_private *iqs620_pwm;
        int ret;

        if (!(event_flags & BIT(IQS62X_EVENT_SYS_RESET)))
                return NOTIFY_DONE;

        iqs620_pwm = container_of(notifier, struct iqs620_pwm_private,
                                  notifier);

        mutex_lock(&iqs620_pwm->lock);

        /*
         * The parent MFD driver already prints an error message in the event
         * of a device reset, so nothing else is printed here unless there is
         * an additional failure.
         */
        ret = iqs620_pwm_init(iqs620_pwm, iqs620_pwm->duty_scale);

        mutex_unlock(&iqs620_pwm->lock);

        if (ret) {
                dev_err(iqs620_pwm->dev,
                        "Failed to re-initialize device: %d\n", ret);
                return NOTIFY_BAD;
        }

        return NOTIFY_OK;
}

static const struct pwm_ops iqs620_pwm_ops = {
        .apply = iqs620_pwm_apply,
        .get_state = iqs620_pwm_get_state,
};

static void iqs620_pwm_notifier_unregister(void *context)
{
        struct iqs620_pwm_private *iqs620_pwm = context;
        int ret;

        ret = blocking_notifier_chain_unregister(&iqs620_pwm->iqs62x->nh,
                                                 &iqs620_pwm->notifier);
        if (ret)
                dev_err(iqs620_pwm->dev,
                        "Failed to unregister notifier: %d\n", ret);
}

static int iqs620_pwm_probe(struct platform_device *pdev)
{
        struct iqs62x_core *iqs62x = dev_get_drvdata(pdev->dev.parent);
        struct pwm_chip *chip;
        struct iqs620_pwm_private *iqs620_pwm;
        unsigned int val;
        int ret;

        chip = devm_pwmchip_alloc(&pdev->dev, 1, sizeof(*iqs620_pwm));
        if (IS_ERR(chip))
                return PTR_ERR(chip);

        iqs620_pwm = iqs620_pwm_from_chip(chip);
        iqs620_pwm->dev = &pdev->dev;
        iqs620_pwm->iqs62x = iqs62x;

        ret = regmap_read(iqs62x->regmap, IQS620_PWR_SETTINGS, &val);
        if (ret)
                return ret;

        if (val & IQS620_PWR_SETTINGS_PWM_OUT) {
                ret = regmap_read(iqs62x->regmap, IQS620_PWM_DUTY_CYCLE, &val);
                if (ret)
                        return ret;

                iqs620_pwm->duty_scale = val + 1;
        }

        chip->ops = &iqs620_pwm_ops;

        mutex_init(&iqs620_pwm->lock);

        iqs620_pwm->notifier.notifier_call = iqs620_pwm_notifier;
        ret = blocking_notifier_chain_register(&iqs620_pwm->iqs62x->nh,
                                               &iqs620_pwm->notifier);
        if (ret) {
                dev_err(&pdev->dev, "Failed to register notifier: %d\n", ret);
                return ret;
        }

        ret = devm_add_action_or_reset(&pdev->dev,
                                       iqs620_pwm_notifier_unregister,
                                       iqs620_pwm);
        if (ret)
                return ret;

        ret = devm_pwmchip_add(&pdev->dev, chip);
        if (ret)
                dev_err(&pdev->dev, "Failed to add device: %d\n", ret);

        return ret;
}

static struct platform_driver iqs620_pwm_platform_driver = {
        .driver = {
                .name = "iqs620a-pwm",
        },
        .probe = iqs620_pwm_probe,
};
module_platform_driver(iqs620_pwm_platform_driver);

MODULE_AUTHOR("Jeff LaBundy <jeff@labundy.com>");
MODULE_DESCRIPTION("Azoteq IQS620A PWM Generator");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:iqs620a-pwm");