// SPDX-License-Identifier: GPL-2.0-only
/*
 * Backlight driver for the Kinetic KTD253
 * Based on code and know-how from the Samsung GT-S7710
 * Gareth Phillips <gareth.phillips@samsung.com>
 */
#include <linux/backlight.h>
#include <linux/delay.h>
#include <linux/err.h>
#include <linux/gpio/consumer.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/limits.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/property.h>
#include <linux/slab.h>

/* Current ratio is n/32 from 1/32 to 32/32 */
#define KTD253_MIN_RATIO 1
#define KTD253_MAX_RATIO 32
#define KTD253_DEFAULT_RATIO 13

#define KTD253_T_LOW_NS (200 + 10) /* Additional 10ns as safety factor */
#define KTD253_T_HIGH_NS (200 + 10) /* Additional 10ns as safety factor */
#define KTD253_T_OFF_CRIT_NS 100000 /* 100 us, now it doesn't look good */
#define KTD253_T_OFF_MS 3

struct ktd253_backlight {
        struct device *dev;
        struct backlight_device *bl;
        struct gpio_desc *gpiod;
        u16 ratio;
};

static void ktd253_backlight_set_max_ratio(struct ktd253_backlight *ktd253)
{
        gpiod_set_value_cansleep(ktd253->gpiod, 1);
        ndelay(KTD253_T_HIGH_NS);
        /* We always fall back to this when we power on */
}

static int ktd253_backlight_stepdown(struct ktd253_backlight *ktd253)
{
        /*
         * These GPIO operations absolutely can NOT sleep so no _cansleep
         * suffixes, and no using GPIO expanders on slow buses for this!
         *
         * The maximum number of cycles of the loop is 32  so the time taken
         * should nominally be:
         * (T_LOW_NS + T_HIGH_NS + loop_time) * 32
         *
         * Architectures do not always support ndelay() and we will get a few us
         * instead. If we get to a critical time limit an interrupt has likely
         * occured in the low part of the loop and we need to restart from the
         * top so we have the backlight in a known state.
         */
        u64 ns;

        ns = ktime_get_ns();
        gpiod_set_value(ktd253->gpiod, 0);
        ndelay(KTD253_T_LOW_NS);
        gpiod_set_value(ktd253->gpiod, 1);
        ns = ktime_get_ns() - ns;
        if (ns >= KTD253_T_OFF_CRIT_NS) {
                dev_err(ktd253->dev, "PCM on backlight took too long (%llu ns)\n", ns);
                return -EAGAIN;
        }
        ndelay(KTD253_T_HIGH_NS);
        return 0;
}

static int ktd253_backlight_update_status(struct backlight_device *bl)
{
        struct ktd253_backlight *ktd253 = bl_get_data(bl);
        int brightness = backlight_get_brightness(bl);
        u16 target_ratio;
        u16 current_ratio = ktd253->ratio;
        int ret;

        dev_dbg(ktd253->dev, "new brightness/ratio: %d/32\n", brightness);

        target_ratio = brightness;

        if (target_ratio == current_ratio)
                /* This is already right */
                return 0;

        if (target_ratio == 0) {
                gpiod_set_value_cansleep(ktd253->gpiod, 0);
                /*
                 * We need to keep the GPIO low for at least this long
                 * to actually switch the KTD253 off.
                 */
                msleep(KTD253_T_OFF_MS);
                ktd253->ratio = 0;
                return 0;
        }

        if (current_ratio == 0) {
                ktd253_backlight_set_max_ratio(ktd253);
                current_ratio = KTD253_MAX_RATIO;
        }

        while (current_ratio != target_ratio) {
                /*
                 * These GPIO operations absolutely can NOT sleep so no
                 * _cansleep suffixes, and no using GPIO expanders on
                 * slow buses for this!
                 */
                ret = ktd253_backlight_stepdown(ktd253);
                if (ret == -EAGAIN) {
                        /*
                         * Something disturbed the backlight setting code when
                         * running so we need to bring the PWM back to a known
                         * state. This shouldn't happen too much.
                         */
                        gpiod_set_value_cansleep(ktd253->gpiod, 0);
                        msleep(KTD253_T_OFF_MS);
                        ktd253_backlight_set_max_ratio(ktd253);
                        current_ratio = KTD253_MAX_RATIO;
                } else if (current_ratio == KTD253_MIN_RATIO) {
                        /* After 1/32 we loop back to 32/32 */
                        current_ratio = KTD253_MAX_RATIO;
                } else {
                        current_ratio--;
                }
        }
        ktd253->ratio = current_ratio;

        dev_dbg(ktd253->dev, "new ratio set to %d/32\n", target_ratio);

        return 0;
}

static const struct backlight_ops ktd253_backlight_ops = {
        .options        = BL_CORE_SUSPENDRESUME,
        .update_status  = ktd253_backlight_update_status,
};

static int ktd253_backlight_probe(struct platform_device *pdev)
{
        struct device *dev = &pdev->dev;
        struct backlight_device *bl;
        struct ktd253_backlight *ktd253;
        u32 max_brightness;
        u32 brightness;
        int ret;

        ktd253 = devm_kzalloc(dev, sizeof(*ktd253), GFP_KERNEL);
        if (!ktd253)
                return -ENOMEM;
        ktd253->dev = dev;

        ret = device_property_read_u32(dev, "max-brightness", &max_brightness);
        if (ret)
                max_brightness = KTD253_MAX_RATIO;
        if (max_brightness > KTD253_MAX_RATIO) {
                /* Clamp brightness to hardware max */
                dev_err(dev, "illegal max brightness specified\n");
                max_brightness = KTD253_MAX_RATIO;
        }

        ret = device_property_read_u32(dev, "default-brightness", &brightness);
        if (ret)
                brightness = KTD253_DEFAULT_RATIO;
        if (brightness > max_brightness) {
                /* Clamp default brightness to max brightness */
                dev_err(dev, "default brightness exceeds max brightness\n");
                brightness = max_brightness;
        }

        ktd253->gpiod = devm_gpiod_get(dev, "enable", GPIOD_OUT_LOW);
        if (IS_ERR(ktd253->gpiod))
                return dev_err_probe(dev, PTR_ERR(ktd253->gpiod),
                                     "gpio line missing or invalid.\n");
        gpiod_set_consumer_name(ktd253->gpiod, dev_name(dev));
        /* Bring backlight to a known off state */
        msleep(KTD253_T_OFF_MS);

        bl = devm_backlight_device_register(dev, dev_name(dev), dev, ktd253,
                                            &ktd253_backlight_ops, NULL);
        if (IS_ERR(bl)) {
                dev_err(dev, "failed to register backlight\n");
                return PTR_ERR(bl);
        }
        bl->props.max_brightness = max_brightness;
        /* When we just enable the GPIO line we set max brightness */
        if (brightness) {
                bl->props.brightness = brightness;
                bl->props.power = BACKLIGHT_POWER_ON;
        } else {
                bl->props.brightness = 0;
                bl->props.power = BACKLIGHT_POWER_OFF;
        }

        ktd253->bl = bl;
        platform_set_drvdata(pdev, bl);
        backlight_update_status(bl);

        return 0;
}

static const struct of_device_id ktd253_backlight_of_match[] = {
        { .compatible = "kinetic,ktd253" },
        { .compatible = "kinetic,ktd259" },
        { /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, ktd253_backlight_of_match);

static struct platform_driver ktd253_backlight_driver = {
        .driver = {
                .name = "ktd253-backlight",
                .of_match_table = ktd253_backlight_of_match,
        },
        .probe          = ktd253_backlight_probe,
};
module_platform_driver(ktd253_backlight_driver);

MODULE_AUTHOR("Linus Walleij <linus.walleij@linaro.org>");
MODULE_DESCRIPTION("Kinetic KTD253 Backlight Driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:ktd253-backlight");