转载请注明出处：https://www.cnblogs.com/lialong1st/p/11436190.html

CPU：RK3288

系统：Linux

客户需求是通过 pwm 控制激光的强弱，写驱动前，需要先了解几个相关的概念和相关函数

概念：

PWM：脉冲宽度调试（Pulse width modulation），最典型的应用是调节 LED 的亮度

占空比：高电平或者低电平时间占一个周期时间的比例

驱动中 pwm 相关函数：

/*

 * 功能：申请pwm设备

 * pwm_id：pwm编号

 * label：自定义名称

 */

struct pwm_device *pwm_request(int pwm_id, const char *label);

/*

 * 功能：释放pwm设备

 * pwm：pwm申请到的设备

 */

void pwm_free(struct pwm_device *pwm);

/*

 * 功能：使能pwm

 * pwm：pwm申请到的设备

 */

int pwm_enable(struct pwm_device *pwm);

/*

 * 功能：失能pwm

 * pwm：pwm申请到的设备

 */

void pwm_disable(struct pwm_device *pwm);

/*

 * 功能：设置pwm周期

 * pwm：pwm申请到的设备

 * period：pwm周期时间，单位为ns

 */

void pwm_set_period(struct pwm_device *pwm, unsigned int period);

/*

 * 功能：获取pwm周期

 * pwm：pwm申请到的设备

 * 返回值：pwm周期时间，单位为ns

 */

unsigned int pwm_get_period(struct pwm_device *pwm);

/*

 * 功能：设置pwm有效极性

 * pwm：pwm申请到的设备

 * polarity：pwm有效极性 PWM_POLARITY_NORMAL / PWM_POLARITY_INVERSED

 */

int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity);

/*

 * 功能：配置pwm

 * pwm：pwm申请到的设备

 * duty_ns：pwm占空比时间，单位为ns

 * period_ns：pwm周期时间，单位为ns

 */

int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns);

根据需求，底层给用户提供四个功能接口，包括设置周期时间、获取当前周期时间、设置占空比、获取当前占空比

1、在 dts 中配置 pwm 默认参数

pwm-laser {

    compatible = "pwm-laser";

    status = "okay";

    /* pwm1 */

    pwm-id = <>;

    /* pwm1周期为1ms */

    period = <>;

    /* 占空比默认为0 */

    default-level = <>;

};

&pwm1 {

    status = "okay";

};

2、编写 pwm 驱动，按照需求为用户提供接口

#include <linux/gpio.h>

#include <linux/of_gpio.h>

#include <linux/module.h>

#include <linux/kernel.h>

#include <linux/init.h>

#include <linux/uaccess.h>

#include <linux/fs.h>

#include <linux/platform_device.h>

#include <linux/fb.h>

#include <linux/err.h>

#include <linux/pwm.h>

#include <linux/slab.h>

#include <linux/miscdevice.h>

#include <linux/delay.h>

#define PWM_LASER_SET_PERIOD        _IOW('A', 0x11, unsigned int)

#define PWM_LASER_GET_PERIOD        _IOR('A', 0x12, unsigned int)

#define PWM_LASER_SET_DUTY          _IOW('A', 0x13, unsigned int)

#define PWM_LASER_GET_DUTY          _IOR('A', 0x14, unsigned int)

#define PWM_LASER_ENABLE            _IO('A', 0x15)

#define PWM_LASER_DISABLE           _IO('A', 0x16)

struct pwm_para {

    int pwm_id;

    unsigned int period;

    unsigned int level;

    unsigned int duty;

    struct pwm_device *pwm;

};

struct pwm_para laser;

static void pwm_laser_update(void)

{

    laser.duty = laser.level * laser.period / ;

    pwm_config(laser.pwm, laser.duty, laser.period);

}

static void pwm_laser_enable(void)

{

    pwm_enable(laser.pwm);

}

static void pwm_laser_disable(void)

{

    // 关闭pwm之前将占空比设置为0

    laser.level = ;

    pwm_laser_update();

    pwm_disable(laser.pwm);

}

static void pwm_laser_set_period(unsigned int period)

{

    laser.period = period * ;

    pwm_set_period(laser.pwm, laser.period);

}

static unsigned int pwm_laser_get_period(void)

{

    return (laser.period / );

}

static int pwm_laser_open(struct inode *inode, struct file *filp)

{

    return ;

}

static int pwm_laser_release(struct inode *inode, struct file *filp)

{

    pwm_laser_disable();

    return ;

}

static ssize_t pwm_laser_read(struct file *filp, char __user *buf, size_t len, loff_t *pos)

{

    return ;

}

static ssize_t pwm_laser_write(struct file *filp, const char __user *buf, size_t len, loff_t *pos)

{

    return ;

}

static long pwm_laser_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)

{

    unsigned int period;

    unsigned int level;

    void __user *argp = (void __user *)arg;

    switch (cmd)

    {

        case PWM_LASER_SET_PERIOD:

            if (argp == NULL) {

                printk("laser: invalid argument.");

                return -EINVAL;

            }

            if (copy_from_user(&period, argp, sizeof(unsigned int))) {

                printk("copy_from_user failed.");

                return -EFAULT;

            }

            pwm_laser_set_period(period);

            break;

        case PWM_LASER_GET_PERIOD:

            period = pwm_laser_get_period();

            if (copy_to_user(argp, &period, sizeof(unsigned int))) {

                printk("copy_to_user failed.");

                return -EFAULT;

            }

            break;

        case PWM_LASER_SET_DUTY    :

            if (argp == NULL) {

                printk("laser: invalid argument.");

                return -EINVAL;

            }

            if (copy_from_user(&level, argp, sizeof(unsigned int))) {

                printk("copy_from_user failed.");

                return -EFAULT;

            }

            if ((level < ) || (level > )) {

                printk("laser: invalid argument.");

                return -EINVAL;

            }

            laser.level = level;

            pwm_laser_update();

            break;

        case PWM_LASER_GET_DUTY    :

            if (copy_to_user(argp, &laser.level, sizeof(unsigned int))) {

                printk("copy_to_user failed.");

                return -EFAULT;

            }

            break;

        case PWM_LASER_ENABLE:

            pwm_laser_update();

            pwm_laser_enable();

            break;

        case PWM_LASER_DISABLE:

            pwm_laser_disable();

            break;

        default:

            printk("laser: cmd error!\n");

            return -EFAULT;

    }

    return ;

}

struct file_operations pwm_laser_fops = {

    .owner = THIS_MODULE,

    .open = pwm_laser_open,

    .release = pwm_laser_release,

    .write = pwm_laser_write,

    .read = pwm_laser_read,

    .unlocked_ioctl = pwm_laser_ioctl,

};

struct miscdevice pwm_laser_dev =

{

    .minor  =   MISC_DYNAMIC_MINOR,

    .fops   =   &pwm_laser_fops,

    .name   =   "pwm-laser",

};

static ssize_t pwm_laser_parse_dt(struct platform_device *pdev)

{

    struct device_node *node = pdev->dev.of_node;

    int ret;

    if (!node) {

        dev_err(&pdev->dev, "laser: Device Tree node missing\n");

        return -EINVAL;

    }

    ret = of_property_read_u32(node, "pwm-id", &laser.pwm_id);

    if (ret < ) {

        dev_err(&pdev->dev, "laser: pwm-id missing\n");

        return ret;

    }

    ret = of_property_read_u32(node, "period", &laser.period);

    if (ret < ) {

        dev_err(&pdev->dev, "laser: period missing\n");

        return ret;

    }

    ret = of_property_read_u32(node, "default-level", &laser.level);

    if (ret < ) {

        dev_err(&pdev->dev, "laser: default-level missing\n");

        return ret;

    }

    return ;

}

static void pwm_laser_test(void)

{

    int i = , dir = ;

    pwm_laser_enable();

    while ()

    {

        if (dir == ) {

            laser.level = i++;

            if (i == )

                dir = ;

        } else {

            laser.level = i--;

            if (i == )

                dir = ;

        }

        pwm_laser_update();

        msleep();

    }

    pwm_laser_disable();

}

static int pwm_laser_probe(struct platform_device *pdev)

{

    int ret;

    ret = pwm_laser_parse_dt(pdev);

    if (ret < ) {

        dev_err(&pdev->dev, "laser: Device not found\n");

        return -ENODEV;

    }

    laser.pwm = pwm_request(laser.pwm_id, "pwm-laser");

    if (IS_ERR(laser.pwm)) {

        dev_err(&pdev->dev, "laser: unable to request legacy PWM\n");

        ret = PTR_ERR(laser.pwm);

        return ret;

    }

    // 设置pwm参数

    pwm_laser_update();

    // 设置极性必须在设置参数之后，pwm使能之前，否则会设置失败

    ret = pwm_set_polarity(laser.pwm, PWM_POLARITY_NORMAL);

    if (ret < )

        printk("pwm set polarity fail, ret = %d\n", ret);

    // 调试完屏蔽使能函数，交由app控制

//  pwm_laser_enable();

    misc_register(&pwm_laser_dev);

    // 调试完屏蔽测试函数

//  pwm_laser_test();

    return ;

}

static int pwm_laser_remove(struct platform_device *pdev)

{

    pwm_disable(laser.pwm);

    pwm_free(laser.pwm);

    misc_deregister(&pwm_laser_dev);

    return ;

}

int pwm_laser_suspend(struct device *dev)

{

    return ;

}

int pwm_laser_resume(struct device *dev)

{

    return ;

}

const struct dev_pm_ops pwm_laser_pm_ops = {

    .suspend = pwm_laser_suspend,

    .resume = pwm_laser_resume,

};

static const struct of_device_id of_pwm_laser_match[] = {

    {.compatible = "pwm-laser", },

    {},

};

static struct platform_driver pwm_laser = {

    .probe = pwm_laser_probe,

    .remove = pwm_laser_remove,

    .driver = {

        .name = "pwm-laser",

        .owner = THIS_MODULE,

        .pm = &pwm_laser_pm_ops,

        .of_match_table = of_match_ptr(of_pwm_laser_match),

    },

};

module_platform_driver(pwm_laser);

MODULE_DESCRIPTION("pwm control driver");

MODULE_LICENSE("GPL");

MODULE_AUTHOR("AaronLee");

3、编写用户测试 demo，测试需求中的所有接口

#include <stdio.h>

#include <stdlib.h>

#include <sys/stat.h>

#include <sys/types.h>

#include <sys/ioctl.h>

#include <unistd.h>

#include <fcntl.h>

#define PWM_LASER_SET_PERIOD            _IOW('A', 0x11, unsigned int)

#define PWM_LASER_GET_PERIOD            _IOR('A', 0x12, unsigned int)

#define PWM_LASER_SET_DUTY              _IOW('A', 0x13, unsigned int)

#define PWM_LASER_GET_DUTY              _IOR('A', 0x14, unsigned int)

#define PWM_LASER_ENABLE                _IO('A', 0x15)

#define PWM_LASER_DISABLE               _IO('A', 0x16)

int main(void)

{

    unsigned int i = ;

    int dir = ;

    int duty, period;

    int fd;

    fd = open("/dev/pwm-laser", O_RDWR);

    if (fd < )

    {

            perror("open pwm-laser fail");

            exit();

    }

    /* 获取pwm周期 */

    ioctl(fd, PWM_LASER_GET_PERIOD, &period);

    printf("pwm: period = %d\n", period);

    /* 设置pwm周期为2ms */

    period = ;

    ioctl(fd, PWM_LASER_SET_PERIOD, &period);

    /* 获取pwm占空比 */

    ioctl(fd, PWM_LASER_GET_DUTY, &duty);

    printf("pwm: duty = %d\n", duty);

    /* 使能pwm */

    ioctl(fd, PWM_LASER_ENABLE);

    while()

    {

        /* 设置pwm占空比 */

        ioctl(fd, PWM_LASER_SET_DUTY, &i);

        if (dir == ) {

            i++;

            if (i == )

                dir = ;

        } else {

            i--;

            if (i == )

                dir = ;

        }

        sleep();

    }

    /* 关闭pwm */

    ioctl(fd, PWM_LASER_DISABLE);

    close(fd);

    return ;

}

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