video/backlight/pwm_bl.c

// 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/fb.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;
    bool legacy;
    unsigned int post_pwm_on_delay;
    unsigned int pwm_off_delay;
    int (*notify)(struct device *, int brightness);
    void (*notify_after)(struct device *, int brightness);
    int (*check_fb)(struct device *, struct fb_info *);
    void (*exit)(struct device *);
};

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

    pwm_get_state(pb->pwm, &state);
    if (pb->enabled) {
        return;
    }

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

    state.enabled = true;
    pwm_apply_state(pb->pwm, &state);

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

    if (pb->enable_gpio) {
        gpiod_set_value_cansleep(pb->enable_gpio, 1);
    }

    pb->enabled = true;
}

static void pwm_backlight_power_off(struct pwm_bl_data *pb)
{
    struct pwm_state state;

    pwm_get_state(pb->pwm, &state);
    if (!pb->enabled) {
        return;
    }

    if (pb->enable_gpio) {
        gpiod_set_value_cansleep(pb->enable_gpio, 0);
    }

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

    state.enabled = false;
    state.duty_cycle = 0;
    pwm_apply_state(pb->pwm, &state);

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

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

    pwm_get_state(pb->pwm, &state);

    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);
        pwm_apply_state(pb->pwm, &state);
        pwm_backlight_power_on(pb);
    } else {
        pwm_backlight_power_off(pb);
    }

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

    return 0;
}

static int pwm_backlight_check_fb(struct backlight_device *bl, struct fb_info *info)
{
    struct pwm_bl_data *pb = bl_get_data(bl);

    return !pb->check_fb || pb->check_fb(pb->dev, info);
}

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

#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 *= 0x64;
    if (lightness <= (0x8 * PWM_LUMINANCE_SCALE)) {
        retval = DIV_ROUND_CLOSEST(lightness * 0xa, 0x2349);
    } else {
        retval = (lightness + (0x10 * PWM_LUMINANCE_SCALE)) / 0x74;
        retval *= retval * retval;
        retval += 1ULL << (0x2 * PWM_LUMINANCE_SHIFT - 1);
        retval >>= 0x2 * 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)), 0x1000);

    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 / 0x2;
    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 = 0;
    unsigned int levels_count;
    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;
    }

    data->max_brightness = length / sizeof(u32);

    /* read brightness levels from DT property */
    if (data->max_brightness > 0) {
        size_t size = sizeof(*data->levels) * data->max_brightness;
        unsigned int i, j, n = 0;

        data->levels = devm_kzalloc(dev, size, GFP_KERNEL);
        if (!data->levels) {
            return -ENOMEM;
        }

        ret = of_property_read_u32_array(node, "brightness-levels", data->levels, data->max_brightness);
        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) {
            if (data->max_brightness < 0x2) {
                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.
             */
            for (i = 0; i < data->max_brightness - 1; i++) {
                if ((data->levels[i + 1] - data->levels[i]) / num_steps) {
                    num_levels += num_steps;
                } else {
                    num_levels++;
                }
            }
            num_levels++;
            dev_dbg(dev, "new number of brightness levels: %d\n", num_levels);

            /*
             * Create a new table of brightness levels with all the
             * interpolated steps.
             */
            size = sizeof(*table) * num_levels;
            table = devm_kzalloc(dev, size, GFP_KERNEL);
            if (!table) {
                return -ENOMEM;
            }

            /* Fill the interpolated table. */
            levels_count = 0;
            for (i = 0; i < data->max_brightness - 1; i++) {
                value = data->levels[i];
                n = (data->levels[i + 1] - value) / num_steps;
                if (n > 0) {
                    for (j = 0; j < num_steps; j++) {
                        table[levels_count] = value;
                        value += n;
                        levels_count++;
                    }
                } else {
                    table[levels_count] = data->levels[i];
                    levels_count++;
                }
            }
            table[levels_count] = data->levels[i];

            /*
             * 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;

            /*
             * Reassign max_brightness value to the new total number
             * of brightness levels.
             */
            data->max_brightness = num_levels;
        }

        data->max_brightness--;
    }

    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 (!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.
     */
    if (pb->enable_gpio) {
        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 FB_BLANK_UNBLANK;
    }

    /*
     * 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 ? FB_BLANK_UNBLANK : FB_BLANK_POWERDOWN;
}

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 device_node *node = pdev->dev.of_node;
    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) {
            dev_err(&pdev->dev, "failed to find platform data\n");
            return ret;
        }

        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->check_fb = data->check_fb;
    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 = PTR_ERR(pb->enable_gpio);
        goto err_alloc;
    }

    pb->power_supply = devm_regulator_get(&pdev->dev, "power");
    if (IS_ERR(pb->power_supply)) {
        ret = PTR_ERR(pb->power_supply);
        goto err_alloc;
    }

    pb->pwm = devm_pwm_get(&pdev->dev, NULL);
    if (IS_ERR(pb->pwm) && PTR_ERR(pb->pwm) != -EPROBE_DEFER && !node) {
        dev_err(&pdev->dev, "unable to request PWM, trying legacy API\n");
        pb->legacy = true;
        pb->pwm = pwm_request(data->pwm_id, "pwm-backlight");
    }

    if (IS_ERR(pb->pwm)) {
        ret = PTR_ERR(pb->pwm);
        if (ret != -EPROBE_DEFER) {
            dev_err(&pdev->dev, "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_state(pb->pwm, &state);
    if (ret) {
        dev_err(&pdev->dev, "failed to apply initial PWM state: %d\n", ret);
        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(&pdev->dev, "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;
    }

    pwm_adjust_config(pb->pwm);

    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)) {
        dev_err(&pdev->dev, "failed to register backlight\n");
        ret = PTR_ERR(bl);
        if (pb->legacy) {
            pwm_free(pb->pwm);
        }
        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 int pwm_backlight_remove(struct platform_device *pdev)
{
    struct backlight_device *bl = platform_get_drvdata(pdev);
    struct pwm_bl_data *pb = bl_get_data(bl);

    backlight_device_unregister(bl);
    pwm_backlight_power_off(pb);

    if (pb->exit) {
        pb->exit(&pdev->dev);
    }
    if (pb->legacy) {
        pwm_free(pb->pwm);
    }

    return 0;
}

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);

    pwm_backlight_power_off(pb);
}

#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);

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

    pwm_backlight_power_off(pb);

    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");