// SPDX-License-Identifier: GPL-2.0-only
/*
 * Simple PWM based backlight control, board code has to setup
 * 1) pin configuration so PWM waveforms can output
 * 2) platform_data being correctly configured
 */

#include <linux/delay.h>
#include <linux/gpio/consumer.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/platform_device.h>
#include <linux/backlight.h>
#include <linux/err.h>
#include <linux/pwm.h>
#include <linux/pwm_backlight.h>
#include <linux/regulator/consumer.h>
#include <linux/slab.h>

struct pwm_bl_data {
        struct pwm_device       *pwm;
        struct device           *dev;
        unsigned int            lth_brightness;
        unsigned int            *levels;
        bool                    enabled;
        struct regulator        *power_supply;
        struct gpio_desc        *enable_gpio;
        unsigned int            scale;
        unsigned int            post_pwm_on_delay;
        unsigned int            pwm_off_delay;
        int                     (*notify)(struct device *,
                                          int brightness);
        void                    (*notify_after)(struct device *,
                                        int brightness);
        void                    (*exit)(struct device *);
};

static void pwm_backlight_power_on(struct pwm_bl_data *pb)
{
        int err;

        if (pb->enabled)
                return;

        if (pb->power_supply) {
                err = regulator_enable(pb->power_supply);
                if (err < 0)
                        dev_err(pb->dev, "failed to enable power supply\n");
        }

        if (pb->post_pwm_on_delay)
                msleep(pb->post_pwm_on_delay);

        gpiod_set_value_cansleep(pb->enable_gpio, 1);

        pb->enabled = true;
}

static void pwm_backlight_power_off(struct pwm_bl_data *pb)
{
        if (!pb->enabled)
                return;

        gpiod_set_value_cansleep(pb->enable_gpio, 0);

        if (pb->pwm_off_delay)
                msleep(pb->pwm_off_delay);

        if (pb->power_supply)
                regulator_disable(pb->power_supply);
        pb->enabled = false;
}

static int compute_duty_cycle(struct pwm_bl_data *pb, int brightness, struct pwm_state *state)
{
        unsigned int lth = pb->lth_brightness;
        u64 duty_cycle;

        if (pb->levels)
                duty_cycle = pb->levels[brightness];
        else
                duty_cycle = brightness;

        duty_cycle *= state->period - lth;
        do_div(duty_cycle, pb->scale);

        return duty_cycle + lth;
}

static int pwm_backlight_update_status(struct backlight_device *bl)
{
        struct pwm_bl_data *pb = bl_get_data(bl);
        int brightness = backlight_get_brightness(bl);
        struct pwm_state state;

        if (pb->notify)
                brightness = pb->notify(pb->dev, brightness);

        if (brightness > 0) {
                pwm_get_state(pb->pwm, &state);
                state.duty_cycle = compute_duty_cycle(pb, brightness, &state);
                state.enabled = true;
                pwm_apply_might_sleep(pb->pwm, &state);

                pwm_backlight_power_on(pb);
        } else {
                pwm_backlight_power_off(pb);

                pwm_get_state(pb->pwm, &state);
                state.duty_cycle = 0;
                /*
                 * We cannot assume a disabled PWM to drive its output to the
                 * inactive state. If we have an enable GPIO and/or a regulator
                 * we assume that this isn't relevant and we can disable the PWM
                 * to save power. If however there is neither an enable GPIO nor
                 * a regulator keep the PWM on be sure to get a constant
                 * inactive output.
                 */
                state.enabled = !pb->power_supply && !pb->enable_gpio;
                pwm_apply_might_sleep(pb->pwm, &state);
        }

        if (pb->notify_after)
                pb->notify_after(pb->dev, brightness);

        return 0;
}

static const struct backlight_ops pwm_backlight_ops = {
        .update_status  = pwm_backlight_update_status,
};

#ifdef CONFIG_OF
#define PWM_LUMINANCE_SHIFT     16
#define PWM_LUMINANCE_SCALE     (1 << PWM_LUMINANCE_SHIFT) /* luminance scale */

/*
 * CIE lightness to PWM conversion.
 *
 * The CIE 1931 lightness formula is what actually describes how we perceive
 * light:
 *          Y = (L* / 903.3)           if L* ≤ 8
 *          Y = ((L* + 16) / 116)^3    if L* > 8
 *
 * Where Y is the luminance, the amount of light coming out of the screen, and
 * is a number between 0.0 and 1.0; and L* is the lightness, how bright a human
 * perceives the screen to be, and is a number between 0 and 100.
 *
 * The following function does the fixed point maths needed to implement the
 * above formula.
 */
static u64 cie1931(unsigned int lightness)
{
        u64 retval;

        /*
         * @lightness is given as a number between 0 and 1, expressed
         * as a fixed-point number in scale
         * PWM_LUMINANCE_SCALE. Convert to a percentage, still
         * expressed as a fixed-point number, so the above formulas
         * can be applied.
         */
        lightness *= 100;
        if (lightness <= (8 * PWM_LUMINANCE_SCALE)) {
                retval = DIV_ROUND_CLOSEST(lightness * 10, 9033);
        } else {
                retval = (lightness + (16 * PWM_LUMINANCE_SCALE)) / 116;
                retval *= retval * retval;
                retval += 1ULL << (2*PWM_LUMINANCE_SHIFT - 1);
                retval >>= 2*PWM_LUMINANCE_SHIFT;
        }

        return retval;
}

/*
 * Create a default correction table for PWM values to create linear brightness
 * for LED based backlights using the CIE1931 algorithm.
 */
static
int pwm_backlight_brightness_default(struct device *dev,
                                     struct platform_pwm_backlight_data *data,
                                     unsigned int period)
{
        unsigned int i;
        u64 retval;

        /*
         * Once we have 4096 levels there's little point going much higher...
         * neither interactive sliders nor animation benefits from having
         * more values in the table.
         */
        data->max_brightness =
                min((int)DIV_ROUND_UP(period, fls(period)), 4096);

        data->levels = devm_kcalloc(dev, data->max_brightness,
                                    sizeof(*data->levels), GFP_KERNEL);
        if (!data->levels)
                return -ENOMEM;

        /* Fill the table using the cie1931 algorithm */
        for (i = 0; i < data->max_brightness; i++) {
                retval = cie1931((i * PWM_LUMINANCE_SCALE) /
                                 data->max_brightness) * period;
                retval = DIV_ROUND_CLOSEST_ULL(retval, PWM_LUMINANCE_SCALE);
                if (retval > UINT_MAX)
                        return -EINVAL;
                data->levels[i] = (unsigned int)retval;
        }

        data->dft_brightness = data->max_brightness / 2;
        data->max_brightness--;

        return 0;
}

static int pwm_backlight_parse_dt(struct device *dev,
                                  struct platform_pwm_backlight_data *data)
{
        struct device_node *node = dev->of_node;
        unsigned int num_levels;
        unsigned int num_steps = 0;
        struct property *prop;
        unsigned int *table;
        int length;
        u32 value;
        int ret;

        if (!node)
                return -ENODEV;

        memset(data, 0, sizeof(*data));

        /*
         * These values are optional and set as 0 by default, the out values
         * are modified only if a valid u32 value can be decoded.
         */
        of_property_read_u32(node, "post-pwm-on-delay-ms",
                             &data->post_pwm_on_delay);
        of_property_read_u32(node, "pwm-off-delay-ms", &data->pwm_off_delay);

        /*
         * Determine the number of brightness levels, if this property is not
         * set a default table of brightness levels will be used.
         */
        prop = of_find_property(node, "brightness-levels", &length);
        if (!prop)
                return 0;

        num_levels = length / sizeof(u32);

        /* read brightness levels from DT property */
        if (num_levels > 0) {
                data->levels = devm_kcalloc(dev, num_levels,
                                            sizeof(*data->levels), GFP_KERNEL);
                if (!data->levels)
                        return -ENOMEM;

                ret = of_property_read_u32_array(node, "brightness-levels",
                                                 data->levels,
                                                 num_levels);
                if (ret < 0)
                        return ret;

                ret = of_property_read_u32(node, "default-brightness-level",
                                           &value);
                if (ret < 0)
                        return ret;

                data->dft_brightness = value;

                /*
                 * This property is optional, if is set enables linear
                 * interpolation between each of the values of brightness levels
                 * and creates a new pre-computed table.
                 */
                of_property_read_u32(node, "num-interpolated-steps",
                                     &num_steps);

                /*
                 * Make sure that there is at least two entries in the
                 * brightness-levels table, otherwise we can't interpolate
                 * between two points.
                 */
                if (num_steps) {
                        unsigned int num_input_levels = num_levels;
                        unsigned int i;
                        u32 x1, x2, x, dx;
                        u32 y1, y2;
                        s64 dy;

                        if (num_input_levels < 2) {
                                dev_err(dev, "can't interpolate\n");
                                return -EINVAL;
                        }

                        /*
                         * Recalculate the number of brightness levels, now
                         * taking in consideration the number of interpolated
                         * steps between two levels.
                         */
                        num_levels = (num_input_levels - 1) * num_steps + 1;
                        dev_dbg(dev, "new number of brightness levels: %d\n",
                                num_levels);

                        /*
                         * Create a new table of brightness levels with all the
                         * interpolated steps.
                         */
                        table = devm_kcalloc(dev, num_levels, sizeof(*table),
                                             GFP_KERNEL);
                        if (!table)
                                return -ENOMEM;
                        /*
                         * Fill the interpolated table[x] = y
                         * by draw lines between each (x1, y1) to (x2, y2).
                         */
                        dx = num_steps;
                        for (i = 0; i < num_input_levels - 1; i++) {
                                x1 = i * dx;
                                x2 = x1 + dx;
                                y1 = data->levels[i];
                                y2 = data->levels[i + 1];
                                dy = (s64)y2 - y1;

                                for (x = x1; x < x2; x++) {
                                        table[x] = y1 +
                                                div_s64(dy * (x - x1), dx);
                                }
                        }
                        /* Fill in the last point, since no line starts here. */
                        table[x2] = y2;

                        /*
                         * As we use interpolation lets remove current
                         * brightness levels table and replace for the
                         * new interpolated table.
                         */
                        devm_kfree(dev, data->levels);
                        data->levels = table;
                }

                data->max_brightness = num_levels - 1;
        }

        return 0;
}

static const struct of_device_id pwm_backlight_of_match[] = {
        { .compatible = "pwm-backlight" },
        { }
};

MODULE_DEVICE_TABLE(of, pwm_backlight_of_match);
#else
static int pwm_backlight_parse_dt(struct device *dev,
                                  struct platform_pwm_backlight_data *data)
{
        return -ENODEV;
}

static
int pwm_backlight_brightness_default(struct device *dev,
                                     struct platform_pwm_backlight_data *data,
                                     unsigned int period)
{
        return -ENODEV;
}
#endif

static bool pwm_backlight_is_linear(struct platform_pwm_backlight_data *data)
{
        unsigned int nlevels = data->max_brightness + 1;
        unsigned int min_val = data->levels[0];
        unsigned int max_val = data->levels[nlevels - 1];
        /*
         * Multiplying by 128 means that even in pathological cases such
         * as (max_val - min_val) == nlevels the error at max_val is less
         * than 1%.
         */
        unsigned int slope = (128 * (max_val - min_val)) / nlevels;
        unsigned int margin = (max_val - min_val) / 20; /* 5% */
        int i;

        for (i = 1; i < nlevels; i++) {
                unsigned int linear_value = min_val + ((i * slope) / 128);
                unsigned int delta = abs(linear_value - data->levels[i]);

                if (delta > margin)
                        return false;
        }

        return true;
}

static int pwm_backlight_initial_power_state(const struct pwm_bl_data *pb)
{
        struct device_node *node = pb->dev->of_node;
        bool active = true;

        /*
         * If the enable GPIO is present, observable (either as input
         * or output) and off then the backlight is not currently active.
         * */
        if (pb->enable_gpio && gpiod_get_value_cansleep(pb->enable_gpio) == 0)
                active = false;

        if (pb->power_supply && !regulator_is_enabled(pb->power_supply))
                active = false;

        if (!pwm_is_enabled(pb->pwm))
                active = false;

        /*
         * Synchronize the enable_gpio with the observed state of the
         * hardware.
         */
        gpiod_direction_output(pb->enable_gpio, active);

        /*
         * Do not change pb->enabled here! pb->enabled essentially
         * tells us if we own one of the regulator's use counts and
         * right now we do not.
         */

        /* Not booted with device tree or no phandle link to the node */
        if (!node || !node->phandle)
                return BACKLIGHT_POWER_ON;

        /*
         * If the driver is probed from the device tree and there is a
         * phandle link pointing to the backlight node, it is safe to
         * assume that another driver will enable the backlight at the
         * appropriate time. Therefore, if it is disabled, keep it so.
         */
        return active ? BACKLIGHT_POWER_ON : BACKLIGHT_POWER_OFF;
}

static int pwm_backlight_probe(struct platform_device *pdev)
{
        struct platform_pwm_backlight_data *data = dev_get_platdata(&pdev->dev);
        struct platform_pwm_backlight_data defdata;
        struct backlight_properties props;
        struct backlight_device *bl;
        struct pwm_bl_data *pb;
        struct pwm_state state;
        unsigned int i;
        int ret;

        if (!data) {
                ret = pwm_backlight_parse_dt(&pdev->dev, &defdata);
                if (ret < 0)
                        return dev_err_probe(&pdev->dev, ret,
                                             "failed to find platform data\n");

                data = &defdata;
        }

        if (data->init) {
                ret = data->init(&pdev->dev);
                if (ret < 0)
                        return ret;
        }

        pb = devm_kzalloc(&pdev->dev, sizeof(*pb), GFP_KERNEL);
        if (!pb) {
                ret = -ENOMEM;
                goto err_alloc;
        }

        pb->notify = data->notify;
        pb->notify_after = data->notify_after;
        pb->exit = data->exit;
        pb->dev = &pdev->dev;
        pb->enabled = false;
        pb->post_pwm_on_delay = data->post_pwm_on_delay;
        pb->pwm_off_delay = data->pwm_off_delay;

        pb->enable_gpio = devm_gpiod_get_optional(&pdev->dev, "enable",
                                                  GPIOD_ASIS);
        if (IS_ERR(pb->enable_gpio)) {
                ret = dev_err_probe(&pdev->dev, PTR_ERR(pb->enable_gpio),
                                    "failed to acquire enable GPIO\n");
                goto err_alloc;
        }

        pb->power_supply = devm_regulator_get_optional(&pdev->dev, "power");
        if (IS_ERR(pb->power_supply)) {
                ret = PTR_ERR(pb->power_supply);
                if (ret == -ENODEV) {
                        pb->power_supply = NULL;
                } else {
                        dev_err_probe(&pdev->dev, ret,
                                      "failed to acquire power regulator\n");
                        goto err_alloc;
                }
        }

        pb->pwm = devm_pwm_get(&pdev->dev, NULL);
        if (IS_ERR(pb->pwm)) {
                ret = dev_err_probe(&pdev->dev, PTR_ERR(pb->pwm),
                                    "unable to request PWM\n");
                goto err_alloc;
        }

        dev_dbg(&pdev->dev, "got pwm for backlight\n");

        /* Sync up PWM state. */
        pwm_init_state(pb->pwm, &state);

        /*
         * The DT case will set the pwm_period_ns field to 0 and store the
         * period, parsed from the DT, in the PWM device. For the non-DT case,
         * set the period from platform data if it has not already been set
         * via the PWM lookup table.
         */
        if (!state.period && (data->pwm_period_ns > 0))
                state.period = data->pwm_period_ns;

        ret = pwm_apply_might_sleep(pb->pwm, &state);
        if (ret) {
                dev_err_probe(&pdev->dev, ret,
                              "failed to apply initial PWM state");
                goto err_alloc;
        }

        memset(&props, 0, sizeof(struct backlight_properties));

        if (data->levels) {
                pb->levels = data->levels;

                /*
                 * For the DT case, only when brightness levels is defined
                 * data->levels is filled. For the non-DT case, data->levels
                 * can come from platform data, however is not usual.
                 */
                for (i = 0; i <= data->max_brightness; i++)
                        if (data->levels[i] > pb->scale)
                                pb->scale = data->levels[i];

                if (pwm_backlight_is_linear(data))
                        props.scale = BACKLIGHT_SCALE_LINEAR;
                else
                        props.scale = BACKLIGHT_SCALE_NON_LINEAR;
        } else if (!data->max_brightness) {
                /*
                 * If no brightness levels are provided and max_brightness is
                 * not set, use the default brightness table. For the DT case,
                 * max_brightness is set to 0 when brightness levels is not
                 * specified. For the non-DT case, max_brightness is usually
                 * set to some value.
                 */

                /* Get the PWM period (in nanoseconds) */
                pwm_get_state(pb->pwm, &state);

                ret = pwm_backlight_brightness_default(&pdev->dev, data,
                                                       state.period);
                if (ret < 0) {
                        dev_err_probe(&pdev->dev, ret,
                                      "failed to setup default brightness table\n");
                        goto err_alloc;
                }

                for (i = 0; i <= data->max_brightness; i++) {
                        if (data->levels[i] > pb->scale)
                                pb->scale = data->levels[i];

                        pb->levels = data->levels;
                }

                props.scale = BACKLIGHT_SCALE_NON_LINEAR;
        } else {
                /*
                 * That only happens for the non-DT case, where platform data
                 * sets the max_brightness value.
                 */
                pb->scale = data->max_brightness;
        }

        pb->lth_brightness = data->lth_brightness * (div_u64(state.period,
                                pb->scale));

        props.type = BACKLIGHT_RAW;
        props.max_brightness = data->max_brightness;
        bl = backlight_device_register(dev_name(&pdev->dev), &pdev->dev, pb,
                                       &pwm_backlight_ops, &props);
        if (IS_ERR(bl)) {
                ret = dev_err_probe(&pdev->dev, PTR_ERR(bl),
                                    "failed to register backlight\n");
                goto err_alloc;
        }

        if (data->dft_brightness > data->max_brightness) {
                dev_warn(&pdev->dev,
                         "invalid default brightness level: %u, using %u\n",
                         data->dft_brightness, data->max_brightness);
                data->dft_brightness = data->max_brightness;
        }

        bl->props.brightness = data->dft_brightness;
        bl->props.power = pwm_backlight_initial_power_state(pb);
        backlight_update_status(bl);

        platform_set_drvdata(pdev, bl);
        return 0;

err_alloc:
        if (data->exit)
                data->exit(&pdev->dev);
        return ret;
}

static void pwm_backlight_remove(struct platform_device *pdev)
{
        struct backlight_device *bl = platform_get_drvdata(pdev);
        struct pwm_bl_data *pb = bl_get_data(bl);
        struct pwm_state state;

        backlight_device_unregister(bl);
        pwm_backlight_power_off(pb);
        pwm_get_state(pb->pwm, &state);
        state.duty_cycle = 0;
        state.enabled = false;
        pwm_apply_might_sleep(pb->pwm, &state);

        if (pb->exit)
                pb->exit(&pdev->dev);
}

static void pwm_backlight_shutdown(struct platform_device *pdev)
{
        struct backlight_device *bl = platform_get_drvdata(pdev);
        struct pwm_bl_data *pb = bl_get_data(bl);
        struct pwm_state state;

        pwm_backlight_power_off(pb);
        pwm_get_state(pb->pwm, &state);
        state.duty_cycle = 0;
        state.enabled = false;
        pwm_apply_might_sleep(pb->pwm, &state);
}

#ifdef CONFIG_PM_SLEEP
static int pwm_backlight_suspend(struct device *dev)
{
        struct backlight_device *bl = dev_get_drvdata(dev);
        struct pwm_bl_data *pb = bl_get_data(bl);
        struct pwm_state state;

        if (pb->notify)
                pb->notify(pb->dev, 0);

        pwm_backlight_power_off(pb);

        /*
         * Note that disabling the PWM doesn't guarantee that the output stays
         * at its inactive state. However without the PWM disabled, the PWM
         * driver refuses to suspend. So disable here even though this might
         * enable the backlight on poorly designed boards.
         */
        pwm_get_state(pb->pwm, &state);
        state.duty_cycle = 0;
        state.enabled = false;
        pwm_apply_might_sleep(pb->pwm, &state);

        if (pb->notify_after)
                pb->notify_after(pb->dev, 0);

        return 0;
}

static int pwm_backlight_resume(struct device *dev)
{
        struct backlight_device *bl = dev_get_drvdata(dev);

        backlight_update_status(bl);

        return 0;
}
#endif

static const struct dev_pm_ops pwm_backlight_pm_ops = {
#ifdef CONFIG_PM_SLEEP
        .suspend = pwm_backlight_suspend,
        .resume = pwm_backlight_resume,
        .poweroff = pwm_backlight_suspend,
        .restore = pwm_backlight_resume,
#endif
};

static struct platform_driver pwm_backlight_driver = {
        .driver         = {
                .name           = "pwm-backlight",
                .pm             = &pwm_backlight_pm_ops,
                .of_match_table = of_match_ptr(pwm_backlight_of_match),
        },
        .probe          = pwm_backlight_probe,
        .remove         = pwm_backlight_remove,
        .shutdown       = pwm_backlight_shutdown,
};

module_platform_driver(pwm_backlight_driver);

MODULE_DESCRIPTION("PWM based Backlight Driver");
MODULE_LICENSE("GPL v2");
MODULE_ALIAS("platform:pwm-backlight");