一、簡介： platform總線是一種虛擬的總線，相應(yīng)的設(shè)備則為platform_device，而驅(qū)動(dòng)則platform_driver。Linux 2.6的設(shè)備驅(qū)動(dòng)模型中，把I2C、RTC、LCD等都?xì)w納為platform_device。 總線將設(shè)備和驅(qū)動(dòng)綁定，在系統(tǒng)每注冊(cè)一個(gè)設(shè)備的時(shí)候，會(huì)尋找與之匹配的驅(qū)動(dòng)；相反的，在系統(tǒng)每注冊(cè)一個(gè)驅(qū)動(dòng)的時(shí)候，會(huì)尋找與之匹配的設(shè)備，而匹配由總線完成。 二、驅(qū)動(dòng)設(shè)備模型 ① Linux2.6系統(tǒng)中定義了一個(gè)bus_type的platform總線實(shí)例platform_bus_type：

struct bus_type platform_bus_type = {  
    .name       = "platform",  
    .dev_attrs  = platform_dev_attrs,  
    .match      = platform_match,       //設(shè)備和驅(qū)動(dòng)使用match函數(shù)來判斷是否匹配  
    .uevent     = platform_uevent,  
    .pm     = PLATFORM_PM_OPS_PTR,  
};  

/* platform_match函數(shù)用于匹配總線中的驅(qū)動(dòng)和設(shè)備 */  
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函數(shù)首先判斷是否platform_driver中定義了id_table，如果有則使用id_table來進(jìn)行匹配。 否則，判斷platform_device和platform_driver成員里的name，如果二者的name字段相同則匹配，如果匹配則調(diào)用platform_driver的probe函數(shù)。 ② platform_driver 結(jié)構(gòu)體:

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結(jié)構(gòu)體有device_driver成員，該成員的各自字段如上所示，device_driver也有probe、remove、shutdown等函數(shù)，在平臺(tái)驅(qū)動(dòng)注冊(cè)的時(shí)候被初始化。 前面說過，當(dāng)系統(tǒng)中存在有平臺(tái)設(shè)備和平臺(tái)驅(qū)動(dòng)通過總線的match函數(shù)匹配后則會(huì)調(diào)用platform_driver的probe函數(shù)，參數(shù)為platform_device，有時(shí)候也通過id_table來判斷是否匹配。

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

②-Ⅰ 平臺(tái)驅(qū)動(dòng)的注冊(cè)使用platform_driver_register函數(shù)：

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，該driver的類型為device_driver，設(shè)置driver的bus為platform_bus_type； 設(shè)置driver的probe為platform_drv_probe； 設(shè)置driver的remove為platform_drv_remove； 設(shè)置driver的shutdown為platform_drv_shutdown； 設(shè)置driver的suspend為platform_drv_suspend； 設(shè)置driver的resume為platform_drv_resume，最后調(diào)用driver_register函數(shù)來注冊(cè)平臺(tái)驅(qū)動(dòng)。 ②-Ⅱ 平臺(tái)驅(qū)動(dòng)的注銷使用platform_driver_unregister函數(shù)：

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

③ platform_device 結(jié)構(gòu)體:

struct platform_device {  
    const char  * name;         /* 名字 */  
    int     id;  
    struct device   dev;  
    u32     num_resources;      /* 資源總數(shù) */  
    struct resource * resource; /* 資源 */  

    struct platform_device_id   *id_entry;  
};  

其中有個(gè)重要的成員是resource，是設(shè)備的資源信息，如IO地址，中斷號(hào)等。

struct resource {  
    resource_size_t start;      //資源的起始值  
    resource_size_t end;        //資源的結(jié)束值  
    const char *name;  
    unsigned long flags;        //資源的類型，如IORESOURCE_IO,IORESOURCE_MEM,IORESOURCE_IRQ,IORESOURCE_DMA  
    struct resource *parent, *sibling, *child;  
};  

有的設(shè)備可能有多個(gè)資源，通常使用platform_get_resource函數(shù)來獲取資源

/** 
 * 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 平臺(tái)設(shè)備的注冊(cè)，使用platform_device_register函數(shù)：

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

platform_device_register函數(shù)先通過device_initialize函數(shù)初始化platform_device的device成員，然后調(diào)用platform_device_add向內(nèi)核添加一個(gè)平臺(tái)設(shè)備。

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

    if (!pdev)  /* 如果pdev為空則返回EINVAL */  
        return -EINVAL;  

    /* 如果pdev->dev.parent為空則將pdev->dev.parent設(shè)置為platform_bus */  
    if (!pdev->dev.parent)  
        pdev->dev.parent = &platform_bus;  

    pdev->dev.bus = &platform_bus_type;  /* 設(shè)置總線類型 */  

    if (pdev->id != -1)      /* 如果id = -1則表示自動(dòng)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]; /* 獲取資源 */  

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

        p = r->parent;  
        if (!p) {  
            if (resource_type(r) == IORESOURCE_MEM) /* 設(shè)置資源類型 */  
                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));  

    /* 向內(nèi)核添加一個(gè)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最終調(diào)用device_add來完成平臺(tái)設(shè)備的注冊(cè)。 ③-Ⅱ 平臺(tái)設(shè)備的注銷，使用platform_device_unregister函數(shù)：

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

platform_device_unregister函數(shù)調(diào)用platform_device_del函數(shù)來注銷平臺(tái)設(shè)備

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函數(shù)調(diào)用device_del函數(shù)來刪除平臺(tái)設(shè)備。 相應(yīng)地，要釋放資源應(yīng)調(diào)用release_resource函數(shù)，前提是資源的類型為IORESOURCE_MEM或者IORESOURCE_IO

三、用platform總線設(shè)備驅(qū)動(dòng)來點(diǎn)亮led

定義平臺(tái)設(shè)備驅(qū)動(dòng)：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");
    /* 配置為輸出 */
    *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)
    {
        // 點(diǎn)燈
        *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;


    /* 注冊(cè)字符設(shè)備驅(qū)動(dòng)程序 */
    printk("led_probe, found ledn");
    major = register_chrdev(0,"czgled",&led_fops); // 注冊(cè)字符設(shè)備驅(qū)動(dòng)程序 ， 0表示系統(tǒng)自動(dòng)分配主設(shè)備號(hào)
    cls = class_create(THIS_MODULE,"czgled");// 創(chuàng)建類"czg_led"
    class_device_create(cls,NULL,MKDEV(major,0),NULL,"led");/* /dev/led */ 
    return 0;
}

static int led_remove(struct platform_device *pdev)
{
    /* 卸載字符設(shè)備驅(qū)動(dòng)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/設(shè)置platform_driver */
struct platform_driver led_drv = {
    .probe      = led_probe, // 匹配成功后將調(diào)用的函數(shù)
    .remove     = led_remove, // 與pobe功能相關(guān),做清理工作
    .driver     = {
        .name   = "czgled", //必須和platform_device的name一樣
    }
};

/* 注冊(cè)一個(gè)platform_driver */
static int led_drv_init(void)
{
    platform_driver_register(&led_drv);
    return 0;
}
/* 卸載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");

定義平臺(tái)設(shè)備：led_dev.c

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

static struct resource led_resource[] = {
    [0] = {
        .start = 0x56000050,// gpfcon寄存器開始地址
        .end   = 0x56000050 + 8 - 1, // gpfcon寄存器結(jié)束地址
        .flags = IORESOURCE_MEM, // 標(biāo)志
    },
    [1] = {
        .start = 4, // gpfdat 4
        .end   = 4,
        .flags = IORESOURCE_IRQ, // 標(biāo)記
    }

};

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

/* 分配/設(shè)置platform_device */
static struct platform_device led_dev = {
    .name         = "czgled", // 必須和platform_driver內(nèi)嵌的driver.name一樣
    .id       = -1,
    .num_resources    = ARRAY_SIZE(led_resource), // 資源大小
    .resource     = led_resource, // 前面的資源數(shù)組
    .dev = { 
        .release = led_release,  // 必須設(shè)置，空的也可以
    },
};
/* 注冊(cè)一個(gè)platform_device */
static int led_dev_init(void)
{
    platform_device_register(&led_dev);
    return 0;
}
/* 卸載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

測試程序：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;
}