pwm_bl.c

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/*
 * linux/drivers/video/backlight/pwm_bl.c
 *
 * simple PWM based backlight control, board code has to setup
 * 1) pin configuration so PWM waveforms can output
 * 2) platform_data being correctly configured
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#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/slab.h>

struct pwm_bl_data {
    struct pwm_device   *pwm;
    struct device       *dev;
    unsigned int        period;
    unsigned int        lth_brightness;
    unsigned int        *levels;
    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 int pwm_backlight_update_status(struct backlight_device *bl)
{
    struct pwm_bl_data *pb = dev_get_drvdata(&bl->dev);
    int brightness = bl->props.brightness;
    int max = bl->props.max_brightness;

    if (bl->props.power != FB_BLANK_UNBLANK)
        brightness = 0;

    if (bl->props.fb_blank != FB_BLANK_UNBLANK)
        brightness = 0;

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

    if (brightness == 0) {
        pwm_config(pb->pwm, 0, pb->period);
        pwm_disable(pb->pwm);
    } else {
        int duty_cycle;

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

        duty_cycle = pb->lth_brightness +
             (duty_cycle * (pb->period - pb->lth_brightness) / max);
        pwm_config(pb->pwm, duty_cycle, pb->period);
        pwm_enable(pb->pwm);
    }

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

    return 0;
}

static int pwm_backlight_get_brightness(struct backlight_device *bl)
{
    return bl->props.brightness;
}

static int pwm_backlight_check_fb(struct backlight_device *bl,
                  struct fb_info *info)
{
    struct pwm_bl_data *pb = dev_get_drvdata(&bl->dev);

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

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

#ifdef CONFIG_OF
static int pwm_backlight_parse_dt(struct device *dev,
                  struct platform_pwm_backlight_data *data)
{
    struct device_node *node = dev->of_node;
    struct property *prop;
    int length;
    u32 value;
    int ret;

    if (!node)
        return -ENODEV;

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

    /* determine the number of brightness levels */
    prop = of_find_property(node, "brightness-levels", &length);
    if (!prop)
        return -EINVAL;

    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;

        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;

        if (value >= data->max_brightness) {
            dev_warn(dev, "invalid default brightness level: %u, using %u\n",
                 value, data->max_brightness - 1);
            value = data->max_brightness - 1;
        }

        data->dft_brightness = value;
        data->max_brightness--;
    }

    /*
     * TODO: Most users of this driver use a number of GPIOs to control
     *       backlight power. Support for specifying these needs to be
     *       added.
     */

    return 0;
}

static 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;
}
#endif

static int pwm_backlight_probe(struct platform_device *pdev)
{
    struct platform_pwm_backlight_data *data = pdev->dev.platform_data;
    struct platform_pwm_backlight_data defdata;
    struct backlight_properties props;
    struct backlight_device *bl;
    struct pwm_bl_data *pb;
    unsigned int max;
    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) {
        dev_err(&pdev->dev, "no memory for state\n");
        ret = -ENOMEM;
        goto err_alloc;
    }

    if (data->levels) {
        max = data->levels[data->max_brightness];
        pb->levels = data->levels;
    } else
        max = data->max_brightness;

    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->pwm = devm_pwm_get(&pdev->dev, NULL);
    if (IS_ERR(pb->pwm)) {
        dev_err(&pdev->dev, "unable to request PWM, trying legacy API\n");

        pb->pwm = pwm_request(data->pwm_id, "pwm-backlight");
        if (IS_ERR(pb->pwm)) {
            dev_err(&pdev->dev, "unable to request legacy PWM\n");
            ret = PTR_ERR(pb->pwm);
            goto err_alloc;
        }
    }

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

    /*
     * 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 (data->pwm_period_ns > 0)
        pwm_set_period(pb->pwm, data->pwm_period_ns);

    pb->period = pwm_get_period(pb->pwm);
    pb->lth_brightness = data->lth_brightness * (pb->period / max);

    memset(&props, 0, sizeof(struct backlight_properties));
    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);
        goto err_alloc;
    }

    bl->props.brightness = data->dft_brightness;
    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 = dev_get_drvdata(&bl->dev);

    backlight_device_unregister(bl);
    pwm_config(pb->pwm, 0, pb->period);
    pwm_disable(pb->pwm);
    if (pb->exit)
        pb->exit(&pdev->dev);
    return 0;
}

#ifdef CONFIG_PM
static int pwm_backlight_suspend(struct device *dev)
{
    struct backlight_device *bl = dev_get_drvdata(dev);
    struct pwm_bl_data *pb = dev_get_drvdata(&bl->dev);

    if (pb->notify)
        pb->notify(pb->dev, 0);
    pwm_config(pb->pwm, 0, pb->period);
    pwm_disable(pb->pwm);
    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;
}

static SIMPLE_DEV_PM_OPS(pwm_backlight_pm_ops, pwm_backlight_suspend,
             pwm_backlight_resume);

#endif

static struct platform_driver pwm_backlight_driver = {
    .driver     = {
        .name       = "pwm-backlight",
        .owner      = THIS_MODULE,
#ifdef CONFIG_PM
        .pm     = &pwm_backlight_pm_ops,
#endif
        .of_match_table = of_match_ptr(pwm_backlight_of_match),
    },
    .probe      = pwm_backlight_probe,
    .remove     = pwm_backlight_remove,
};

module_platform_driver(pwm_backlight_driver);

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