Linux驱动-platform总线设备驱动

[导读]一、简介： platform总线是一种虚拟的总线，相应的设备则为platform_device，而驱动则platform_driver。Linux 2.6的设备驱动模型中，把I2C、RTC、LCD等

一、简介： platform总线是一种虚拟的总线，相应的设备则为platform_device，而驱动则platform_driver。Linux 2.6的设备驱动模型中，把I2C、RTC、LCD等都归纳为platform_device。总线将设备和驱动绑定，在系统每注册一个设备的时候，会寻找与之匹配的驱动；相反的，在系统每注册一个驱动的时候，会寻找与之匹配的设备，而匹配由总线完成。二、驱动设备模型 ① Linux2.6系统中定义了一个bus_type的platform总线实例platform_bus_type：

struct bus_type platform_bus_type = {  
    .name       = "platform",  
    .dev_attrs  = platform_dev_attrs,  
    .match      = platform_match,       //设备和驱动使用match函数来判断是否匹配  
    .uevent     = platform_uevent,  
    .pm     = PLATFORM_PM_OPS_PTR,  
};

/* platform_match函数用于匹配总线中的驱动和设备 */  
static int platform_match(struct device *dev, struct device_driver *drv)  
{  
    struct platform_device *pdev = to_platform_device(dev);  
    struct platform_driver *pdrv = to_platform_driver(drv);  

    /* match against the id table first */  
    if (pdrv->id_table)  
        return platform_match_id(pdrv->id_table, pdev) != NULL;  

    /* fall-back to driver name match */  
    return (strcmp(pdev->name, drv->name) == 0);  
}

platform_match函数首先判断是否platform_driver中定义了id_table，如果有则使用id_table来进行匹配。否则，判断platform_device和platform_driver成员里的name，如果二者的name字段相同则匹配，如果匹配则调用platform_driver的probe函数。 ② platform_driver 结构体:

struct device_driver {  
    const char      *name;  
    struct bus_type     *bus;  
    struct module       *owner;  
    const char      *mod_name;  /* used for built-in modules */  
    bool suppress_bind_attrs;   /* disables bind/unbind via sysfs */  
    const struct of_device_id   *of_match_table;  
    const struct acpi_device_id *acpi_match_table;  
    int (*probe) (struct device *dev);  
    int (*remove) (struct device *dev);  
    void (*shutdown) (struct device *dev);  
    int (*suspend) (struct device *dev, pm_message_t state);  
    int (*resume) (struct device *dev);  
    const struct attribute_group **groups;  
    const struct dev_pm_ops *pm;  
    struct driver_private *p;  
};

platform_driver结构体有device_driver成员，该成员的各自字段如上所示，device_driver也有probe、remove、shutdown等函数，在平台驱动注册的时候被初始化。前面说过，当系统中存在有平台设备和平台驱动通过总线的match函数匹配后则会调用platform_driver的probe函数，参数为platform_device，有时候也通过id_table来判断是否匹配。

struct platform_device_id {  
    char name[PLATFORM_NAME_SIZE];  
    kernel_ulong_t driver_data  
            __attribute__((aligned(sizeof(kernel_ulong_t))));  
};

②-Ⅰ 平台驱动的注册使用platform_driver_register函数：

int platform_driver_register(struct platform_driver *drv)  
{  
    drv->driver.bus = &platform_bus_type;  
    if (drv->probe)  
        drv->driver.probe = platform_drv_probe;  
    if (drv->remove)  
        drv->driver.remove = platform_drv_remove;  
    if (drv->shutdown)  
        drv->driver.shutdown = platform_drv_shutdown;  
    if (drv->suspend)  
        drv->driver.suspend = platform_drv_suspend;  
    if (drv->resume)  
        drv->driver.resume = platform_drv_resume;  
    return driver_register(&drv->driver);  
}

先初始化platform_driver里的driver，该driver的类型为device_driver，设置driver的bus为platform_bus_type；设置driver的probe为platform_drv_probe；设置driver的remove为platform_drv_remove；设置driver的shutdown为platform_drv_shutdown；设置driver的suspend为platform_drv_suspend；设置driver的resume为platform_drv_resume，最后调用driver_register函数来注册平台驱动。 ②-Ⅱ 平台驱动的注销使用platform_driver_unregister函数：

void platform_driver_unregister(struct platform_driver *drv)  
{  
    driver_unregister(&drv->driver);  
}

③ platform_device 结构体:

struct platform_device {  
    const char  * name;         /* 名字 */  
    int     id;  
    struct device   dev;  
    u32     num_resources;      /* 资源总数 */  
    struct resource * resource; /* 资源 */  

    struct platform_device_id   *id_entry;  
};

其中有个重要的成员是resource，是设备的资源信息，如IO地址，中断号等。

struct resource {  
    resource_size_t start;      //资源的起始值  
    resource_size_t end;        //资源的结束值  
    const char *name;  
    unsigned long flags;        //资源的类型，如IORESOURCE_IO,IORESOURCE_MEM,IORESOURCE_IRQ,IORESOURCE_DMA  
    struct resource *parent, *sibling, *child;  
};

有的设备可能有多个资源，通常使用platform_get_resource函数来获取资源

/** 
 * platform_get_resource - get a resource for a device 
 * @dev: platform device 
 * @type: resource type 
 * @num: resource index 
 */  
struct resource *platform_get_resource(struct platform_device *dev,  
                       unsigned int type, unsigned int num)  
{  
    int i;  

    for (i = 0; i < dev->num_resources; i++) {  
        struct resource *r = &dev->resource[i];  

        if (type == resource_type(r) && num-- == 0)  
            return r;  
    }  
    return NULL;  
}

③-Ⅰ 平台设备的注册，使用platform_device_register函数：

int platform_device_register(struct platform_device *pdev)  
{  
    device_initialize(&pdev->dev);  
    return platform_device_add(pdev);  
}

platform_device_register函数先通过device_initialize函数初始化platform_device的device成员，然后调用platform_device_add向内核添加一个平台设备。

int platform_device_add(struct platform_device *pdev)  
{  
    int i, ret = 0;  

    if (!pdev)  /* 如果pdev为空则返回EINVAL */  
        return -EINVAL;  

    /* 如果pdev->dev.parent为空则将pdev->dev.parent设置为platform_bus */  
    if (!pdev->dev.parent)  
        pdev->dev.parent = &platform_bus;  

    pdev->dev.bus = &platform_bus_type;  /* 设置总线类型 */  

    if (pdev->id != -1)      /* 如果id = -1则表示自动分配name */  
        dev_set_name(&pdev->dev, "%s.%d", pdev->name,  pdev->id);  
    else  
        dev_set_name(&pdev->dev, pdev->name);  

    for (i = 0; i < pdev->num_resources; i++) {  
        struct resource *p, *r = &pdev->resource[i]; /* 获取资源 */  

        if (r->name == NULL)  
            r->name = dev_name(&pdev->dev);  

        p = r->parent;  
        if (!p) {  
            if (resource_type(r) == IORESOURCE_MEM) /* 设置资源类型 */  
                p = &iomem_resource;  
            else if (resource_type(r) == IORESOURCE_IO)  
                p = &ioport_resource;  
        }  

        if (p && insert_resource(p, r)) {  
            printk(KERN_ERR  
                   "%s: failed to claim resource %dn",  
                   dev_name(&pdev->dev), i);  
            ret = -EBUSY;  
            goto failed;  
        }  
    }  

    pr_debug("Registering platform device '%s'. Parent at %sn",  
         dev_name(&pdev->dev), dev_name(pdev->dev.parent));  

    /* 向内核添加一个device */  
    ret = device_add(&pdev->dev);  
    if (ret == 0)  
        return ret;  

 failed:  
    while (--i >= 0) {  
        struct resource *r = &pdev->resource[i];  
        unsigned long type = resource_type(r);  

        if (type == IORESOURCE_MEM || type == IORESOURCE_IO)  
            release_resource(r);  
    }  

    return ret;  
}

platform_device_add最终调用device_add来完成平台设备的注册。 ③-Ⅱ 平台设备的注销，使用platform_device_unregister函数：

void platform_device_unregister(struct platform_device *pdev)  
{  
    platform_device_del(pdev);  
    platform_device_put(pdev);  
}

platform_device_unregister函数调用platform_device_del函数来注销平台设备

void platform_device_del(struct platform_device *pdev)  
{  
    int i;  

    if (pdev) {  
        device_del(&pdev->dev);  

        for (i = 0; i < pdev->num_resources; i++) {  
            struct resource *r = &pdev->resource[i];  
            unsigned long type = resource_type(r);  

            if (type == IORESOURCE_MEM || type == IORESOURCE_IO)  
                release_resource(r);  
        }  
    }  
}

platform_device_del函数调用device_del函数来删除平台设备。相应地，要释放资源应调用release_resource函数，前提是资源的类型为IORESOURCE_MEM或者IORESOURCE_IO

三、用platform总线设备驱动来点亮led

定义平台设备驱动：led_drv.c

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

static int major;
static struct class *cls;
static volatile unsigned long *gpio_con;
static volatile unsigned long *gpio_dat;
static int pin;

static int led_open(struct inode *inode, struct file *file)
{
    //printk("first_drv_openn");
    /* 配置为输出 */
    *gpio_con &= ~(0x3<<(pin*2));
    *gpio_con |= (0x1<<(pin*2));
    return 0;   
}

static ssize_t led_write(struct file *file, const char __user *buf, size_t count, loff_t * ppos)
{
    int val;

    //printk("first_drv_writen");

    copy_from_user(&val, buf, count); //    copy_to_user();

    if (val == 1)
    {
        // 点灯
        *gpio_dat &= ~(1<start,res->end - res->start +1);
    gpio_dat = gpio_con + 1;

    res = platform_get_resource(pdev,IORESOURCE_IRQ,0);
    pin = res->start;


    /* 注册字符设备驱动程序 */
    printk("led_probe, found ledn");
    major = register_chrdev(0,"czgled",&led_fops); // 注册字符设备驱动程序 ， 0表示系统自动分配主设备号
    cls = class_create(THIS_MODULE,"czgled");// 创建类"czg_led"
    class_device_create(cls,NULL,MKDEV(major,0),NULL,"led");/* /dev/led */ 
    return 0;
}

static int led_remove(struct platform_device *pdev)
{
    /* 卸载字符设备驱动程序 */
    /* iounmap */
    printk("led_remove, remove ledn");
    class_device_destroy(cls,MKDEV(major,0));
    class_destroy(cls);
    unregister_chrdev(major,"czgled");
    iounmap(gpio_con);

    return 0;
}

/* 分配/设置platform_driver */
struct platform_driver led_drv = {
    .probe      = led_probe, // 匹配成功后将调用的函数
    .remove     = led_remove, // 与pobe功能相关,做清理工作
    .driver     = {
        .name   = "czgled", //必须和platform_device的name一样
    }
};

/* 注册一个platform_driver */
static int led_drv_init(void)
{
    platform_driver_register(&led_drv);
    return 0;
}
/* 卸载platform_driver */
static void led_drv_exit(void)
{
    platform_driver_unregister(&led_drv);
}

module_init(led_drv_init);
module_exit(led_drv_exit);

MODULE_LICENSE("GPL");

定义平台设备：led_dev.c

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

static struct resource led_resource[] = {
    [0] = {
        .start = 0x56000050,// gpfcon寄存器开始地址
        .end   = 0x56000050 + 8 - 1, // gpfcon寄存器结束地址
        .flags = IORESOURCE_MEM, // 标志
    },
    [1] = {
        .start = 4, // gpfdat 4
        .end   = 4,
        .flags = IORESOURCE_IRQ, // 标记
    }

};

static void led_release(struct device * dev)
{
}// do nothing  

/* 分配/设置platform_device */
static struct platform_device led_dev = {
    .name         = "czgled", // 必须和platform_driver内嵌的driver.name一样
    .id       = -1,
    .num_resources    = ARRAY_SIZE(led_resource), // 资源大小
    .resource     = led_resource, // 前面的资源数组
    .dev = { 
        .release = led_release,  // 必须设置，空的也可以
    },
};
/* 注册一个platform_device */
static int led_dev_init(void)
{
    platform_device_register(&led_dev);
    return 0;
}
/* 卸载platform_device */
static void led_dev_exit(void)
{
    platform_device_unregister(&led_dev);
}

module_init(led_dev_init);
module_exit(led_dev_exit);

MODULE_LICENSE("GPL");

Makefile：

KERN_DIR = /work/system/linux-2.6.22.6

all:
    make -C $(KERN_DIR) M=`pwd` modules 

clean:
    make -C $(KERN_DIR) M=`pwd` modules clean
    rm -rf modules.order

obj-m += led_drv.o
obj-m += led_dev.o

测试程序：led_test.c

#include 
#include 
#include 
#include 

/* led_test on
 * led_test off
 */
int main(int argc, char **argv)
{
    int fd;
    int val = 1;
    fd = open("/dev/led", O_RDWR);
    if (fd < 0)
    {
        printf("can't open!n");
    }
    if (argc != 2)
    {
        printf("Usage :n");
        printf("%s n", argv[0]);
        return 0;
    }

    if (strcmp(argv[1], "on") == 0)
    {
        val  = 1;
    }
    else
    {
        val = 0;
    }

    write(fd, &val, 4);
    return 1;
}