[系统运维]一、linux驱动开发-8.2-设备树下platform驱动

一、简介

???????之前没用设备树的时候，是分别编写并注册platform_device和platform_driver来表示设备和驱动，如果使用设备树，设备的描述就放在设备树中，因此只需要实现platform_driver就可以了，具体如下：

1.1、创建节点

???????因为platform总线需要通过设备节点的compatible属性值来匹配驱动，所以创建节点的重点是设置好compatible属性值。比如：

1.2、兼容属性

在使用设备树的时候，platform驱动会通过of_match_table来保存兼容属性值，也就表明此驱动兼容哪些设备，可以按照如下设置：

static const struct of_device_id led_of_match[] = {
    { .compatible = "atkmini-gpioled"},
    {}
};

MODULE_DEVICE_TABLE(of, led_of_match);

/*
*platform平台驱动结构体
*/
static struct platform_driver led_platform_driver = {
    .driver = {
        .name = "imx6ul-led",
        .of_match_table = led_of_match,
    },
    .probe = leddev_probe,
    .remove = leddev_remove,
};

? ? ? ?of_device_id是驱动的兼容表，一个驱动可以跟多个设备匹配，这里仅匹配了一个。compatible值跟设备树中的值一致，匹配成功后，对应的probe函数就会执行。

二、驱动编写

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/io.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/of_gpio.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/platform_device.h>

#define LEDDEV_CNT     1     
#define LEDDEV_NAME    "dtsplatled"

#define	LED_ON      1
#define LED_OFF     0

//设备结构体
struct leddev_dev{
	dev_t devid;
	struct cdev cdev;
	struct class *class;
	struct device *device;
	int major;
	int minor;
	struct device_node *nd;		//设备节点
	int led_gpio;				//led所使用的GPIO编号
};

struct leddev_dev leddev;  

static void led_switch(uint8_t sta)
{
	if (sta == LED_ON)
	{
		gpio_set_value(leddev.led_gpio, 0);
	} else if (sta == LED_OFF) {
		gpio_set_value(leddev.led_gpio, 1);
	}
}

static int leddev_open(struct inode *inode, struct file *filp)
{
	filp->private_data = &leddev;
	printk("leddev open!\n");
	return 0;
}

static ssize_t leddev_read(struct file *filp, __user char *buf, size_t count, loff_t *ppos)
{	
	printk("leddev read\n");
	return 0;
}

static ssize_t leddev_write(struct file *filp, const char __user *buf, size_t count, loff_t *oppos)
{
	int ret;
	uint8_t data_buf[1];
	ret = copy_from_user(data_buf, buf, count);
	if (ret < 0)
	{
		printk("write data fail\n");
		return -EFAULT;
	}

	led_switch(data_buf[0]);

	return 0;
}

static int leddev_release(struct inode *inode, struct file *filp)
{
	printk("led release\n");
	return 0;
}

static const struct file_operations leddev_fops = {
	.owner = THIS_MODULE,
	.open  = leddev_open,
	.read  = leddev_read,
	.write = leddev_write,
	.release = leddev_release,
};

/*
*platform驱动的probe函数
*驱动与设备匹配成功以后此函数就会执行
*/

static int leddev_probe(struct platform_device *dev)
{
	int ret = 0;

	printk("led driver and device has match\r\n");

	//通过节点名字查找节点
	leddev.nd = of_find_node_by_name(NULL, "gpioled");
	if (leddev.nd == NULL)
	{
		printk("find %s fail\r\n", "gpioled");
		return -EINVAL;
	}

	//获取GPIO编号
	leddev.led_gpio = of_get_named_gpio(leddev.nd, "gpio", 0);
	if (leddev.led_gpio < 0)
	{
		printk("get gpio fail\r\n");
		return -EINVAL;
	}
	else
	{
		printk("led_gpio value is %d", leddev.led_gpio);
	}

	//设置led状态
	ret = gpio_direction_output(leddev.led_gpio, 0);
	if (ret < 0)
	{
		printk("set led status fail\r\n");
		return -EINVAL;
	}

	//分配设备号
	if (leddev.major) {
		leddev.devid = MKDEV(leddev.major, 0);
		register_chrdev_region(leddev.devid, LEDDEV_CNT, LEDDEV_NAME);
	} else {
		alloc_chrdev_region(&leddev.devid, 0, LEDDEV_CNT, LEDDEV_NAME);
		leddev.major = MAJOR(leddev.devid);
		leddev.minor = MINOR(leddev.devid);
	}
	printk("leddev major=%d, minor= %d\r\n", leddev.major, leddev.minor);
	//初始化cdev
	leddev.cdev.owner = THIS_MODULE;
	cdev_init(&leddev.cdev, &leddev_fops);
	//添加cdev
	cdev_add(&leddev.cdev, leddev.devid, LEDDEV_CNT);
	//创建类
	leddev.class = class_create(THIS_MODULE, LEDDEV_NAME);
	//创建设备
	leddev.device = device_create(leddev.class, NULL, leddev.devid, NULL, LEDDEV_NAME);
	
	return 0;
}

static int leddev_remove(struct platform_device *dev)
{
    led_switch(LED_OFF);

	//删除设备的类
	device_destroy(leddev.class, leddev.devid);
	//删除类
	class_destroy(leddev.class);
	//删除设备
	cdev_del(&leddev.cdev);
	//注销设备号
	unregister_chrdev_region(leddev.devid, LEDDEV_CNT);
}

static const struct of_device_id led_of_match[] = {
	{ .compatible = "atkmini-gpioled"},
	{}
};

/*
*platform平台驱动结构体
*/
static struct platform_driver led_driver = {
    .driver = {
        .name = "imx6ul-led",
		.of_match_table = led_of_match,
    },
    .probe = leddev_probe,
    .remove = leddev_remove,
};

static int __init leddriver_init(void)
{
    return platform_driver_register(&led_driver);
}

static void __exit leddriver_exit(void)
{
    platform_driver_unregister(&led_driver);
		
	printk("newchrdev exit\n");
}

module_init(leddriver_init);
module_exit(leddriver_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("ZK");

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