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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 = <1>; /* pwm1周期为1ms */ period = <1000000>; /* 占空比默认为0 */ default-level = <0>; }; &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 / 100; 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 = 0; pwm_laser_update(); pwm_disable(laser.pwm); } static void pwm_laser_set_period(unsigned int period) { laser.period = period * 1000000; pwm_set_period(laser.pwm, laser.period); } static unsigned int pwm_laser_get_period(void) { return (laser.period / 1000000); } static int pwm_laser_open(struct inode *inode, struct file *filp) { return 0; } static int pwm_laser_release(struct inode *inode, struct file *filp) { pwm_laser_disable(); return 0; } static ssize_t pwm_laser_read(struct file *filp, char __user *buf, size_t len, loff_t *pos) { return 0; } static ssize_t pwm_laser_write(struct file *filp, const char __user *buf, size_t len, loff_t *pos) { return 0; } 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 < 0) || (level > 100)) { 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! "); return -EFAULT; } return 0; } 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 "); return -EINVAL; } ret = of_property_read_u32(node, "pwm-id", &laser.pwm_id); if (ret < 0) { dev_err(&pdev->dev, "laser: pwm-id missing "); return ret; } ret = of_property_read_u32(node, "period", &laser.period); if (ret < 0) { dev_err(&pdev->dev, "laser: period missing "); return ret; } ret = of_property_read_u32(node, "default-level", &laser.level); if (ret < 0) { dev_err(&pdev->dev, "laser: default-level missing "); return ret; } return 0; } static void pwm_laser_test(void) { int i = 0, dir = 0; pwm_laser_enable(); while (1) { if (dir == 0) { laser.level = i++; if (i == 100) dir = 1; } else { laser.level = i--; if (i == 0) dir = 0; } pwm_laser_update(); msleep(100); } pwm_laser_disable(); } static int pwm_laser_probe(struct platform_device *pdev) { int ret; ret = pwm_laser_parse_dt(pdev); if (ret < 0) { dev_err(&pdev->dev, "laser: Device not found "); 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 "); 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 < 0) printk("pwm set polarity fail, ret = %d ", 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 0; } static int pwm_laser_remove(struct platform_device *pdev) { pwm_disable(laser.pwm); pwm_free(laser.pwm); misc_deregister(&pwm_laser_dev); return 0; } int pwm_laser_suspend(struct device *dev) { return 0; } int pwm_laser_resume(struct device *dev) { return 0; } 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 = 0; int dir = 0; int duty, period; int fd; fd = open("/dev/pwm-laser", O_RDWR); if (fd < 0) { perror("open pwm-laser fail"); exit(1); } /* 获取pwm周期 */ ioctl(fd, PWM_LASER_GET_PERIOD, &period); printf("pwm: period = %d ", period); /* 设置pwm周期为2ms */ period = 2; ioctl(fd, PWM_LASER_SET_PERIOD, &period); /* 获取pwm占空比 */ ioctl(fd, PWM_LASER_GET_DUTY, &duty); printf("pwm: duty = %d ", duty); /* 使能pwm */ ioctl(fd, PWM_LASER_ENABLE); while(1) { /* 设置pwm占空比 */ ioctl(fd, PWM_LASER_SET_DUTY, &i); if (dir == 0) { i++; if (i == 100) dir = 1; } else { i--; if (i == 0) dir = 0; } sleep(1); } /* 关闭pwm */ ioctl(fd, PWM_LASER_DISABLE); close(fd); return 0; }