驱动设备模型之总线设备驱动

为了适用要求越来越高的硬件设备需求，linux2.6内核提供了一种全新的内核设备模型。

设备模型三元素：总线、设备、驱动；

第一节：总线

总线是处理器与设备之间的通道，所有的设备通过总线相连；总线由bus_type定义（位于<linux/device.h>

struct bus_type {
    const char        *name;
    struct bus_attribute    *bus_attrs;
    struct device_attribute    *dev_attrs;
    struct driver_attribute    *drv_attrs;

    int (*match)(struct device *dev, struct device_driver *drv);
    int (*uevent)(struct device *dev, struct kobj_uevent_env *env);
    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 dev_pm_ops *pm;
device
    struct subsys_private *p;
};

bus_type结构体中重要的方法：

match：当一个新设备或驱动被添加到这条总线时，该方法被调用。用来判断制定的驱动程序是否能够处理指定的设备。若可以，返回非零值。

uevent：为用户空间产生热插拔事件之前，这个方法允许总线添加环境变量；

bus_attribute: 总线属性，这个结构体如下

struct bus_attribute {
    struct attribute    attr;
    ssize_t (*show)(struct bus_type *bus, char *buf);
    ssize_t (*store)(struct bus_type *bus, const char *buf, size_t count);
};

总线属性的操作方法：

int bus_create_file(struct bus_type *bus,struct bus_attribute *attr)   //创建属性

void bus_remove_file(struct bus_type*bus, struct bus_attribute *attr)   //删除属性

总线的常用操作函数：

int bus_register(struct bus_type * bus)     //总线的注册

void bus_unregister(struct bus_type *bus)   //总线的删除

第二节：设备

linux每个设备又结构体devices来定义（位于linux/device.h），如下：

struct device {
    struct device        *parent;

    struct device_private    *p;

    struct kobject kobj;
    const char        *init_name; /* initial name of the device */
    struct device_type    *type;

    struct mutex        mutex;    /* mutex to synchronize calls to
                     * its driver.
                     */

    struct bus_type    *bus;        /* type of bus device is on */
    struct device_driver *driver;    /* which driver has allocated this
                       device */
    void        *platform_data;    /* Platform specific data, device
                       core doesn't touch it */
    struct dev_pm_info    power;

#ifdef CONFIG_NUMA
    int        numa_node;    /* NUMA node this device is close to */
#endif
    u64        *dma_mask;    /* dma mask (if dma'able device) */
    u64        coherent_dma_mask;/* Like dma_mask, but for
                         alloc_coherent mappings as
                         not all hardware supports
                         64 bit addresses for consistent
                         allocations such descriptors. */

    struct device_dma_parameters *dma_parms;

    struct list_head    dma_pools;    /* dma pools (if dma'ble) */

    struct dma_coherent_mem    *dma_mem; /* internal for coherent mem
                         override */
    /* arch specific additions */
    struct dev_archdata    archdata;
#ifdef CONFIG_OF
    struct device_node    *of_node;
#endif

    dev_t            devt;    /* dev_t, creates the sysfs "dev" */

    spinlock_t        devres_lock;
    struct list_head    devres_head;

    struct klist_node    knode_class;
    struct class        *class;
    const struct attribute_group **groups;    /* optional groups */

    void    (*release)(struct device *dev);
};

设备属性由struct device_attribute描述：

struct device_attribute {
    struct attribute    attr;
    ssize_t (*show)(struct device *dev, struct device_attribute *attr,
            char *buf);
    ssize_t (*store)(struct device *dev, struct device_attribute *attr,
             const char *buf, size_t count);
};

设备属性的常用操作方法：

int device_create_file(struct device *device, struct device_attribute * entry)   //创建属性

void device_remove_file(struct device * dev, struct device_attribute * attr)    //删除属性

设备的常用操作函数：

int device_register(struct device *dev)    //注册一个设备；

void device_unregister(struct device *dev)   //注销设备

注意：一条总线也是个设备，也必须按设备注册；

第三节：驱动

驱动程序由struct device_driver描述,代码如下：

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 */

#if defined(CONFIG_OF)
    const struct of_device_id    *of_match_table;
#endif

    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;
};

驱动属性使用struct driver_attribute来描述，如下：

struct driver_attribute {
    struct attribute attr;
    ssize_t (*show)(struct device_driver *driver, char *buf);
    ssize_t (*store)(struct device_driver *driver, const char *buf,
             size_t count);
};

驱动属性的常用操作方法：

int driver_create_file(struct device_driver * drv,struct driver_attribute * attr)   //创建属性

void driver_remove_file(struct device_driver * drv,struct driver_attribute * attr)  /删除属性

驱动常用的操作函数：

int driver_register(struct device_driver *drv)    //注册驱动

void driver_unregister(struct device_driver *drv)   //注销驱动

 

实例分析：

至此，已经介绍完设备模型的基本结构，下面以一个实例分析三者之间的关系：

bus.c    在sysfs/bus下创建一个总线目录my_bus

#include <linux/device.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/string.h>

MODULE_AUTHOR("David Xie");
MODULE_LICENSE("Dual BSD/GPL");

static char *Version = "$Revision: 1.9 $";

/*比较设备的bus_id与驱动的名字是否匹配，匹配一致则在insmod驱动 时候调用probe函数*/

static int my_match(struct device *dev, struct device_driver *driver)
{
    return !strncmp(dev->bus_id, driver->name, strlen(driver->name));
}

static void my_bus_release(struct device *dev)
{
    printk(KERN_DEBUG "my bus release\n");
}

struct bus_type my_bus_type = {
    .name = "my_bus",
    .match = my_match,
};
    
struct device my_bus = {
    .bus_id   = "my_bus0",
    .release  = my_bus_release
};


/*符号导出
 * Export a simple attribute.
 */
EXPORT_SYMBOL(my_bus);
EXPORT_SYMBOL(my_bus_type);

static ssize_t show_bus_version(struct bus_type *bus, char *buf)
{
    return snprintf(buf, PAGE_SIZE, "%s\n", Version);
}

static BUS_ATTR(version, S_IRUGO, show_bus_version, NULL);


static int __init my_bus_init(void)
{
    int ret;
        
        /*注册总线*/
    ret = bus_register(&my_bus_type);
    if (ret)
        return ret;
        
    /*创建属性文件*/    
    if (bus_create_file(&my_bus_type, &bus_attr_version))
        printk(KERN_NOTICE "Fail to create version attribute!\n");
    
    /*注册总线设备，设备是挂在my_bus总线上的，怎么做的呢？看device.c*/
    ret = device_register(&my_bus);
    if (ret)
        printk(KERN_NOTICE "Fail to register device:my_bus!\n");
        
    return ret;
}

static void my_bus_exit(void)
{
    device_unregister(&my_bus);
    bus_unregister(&my_bus_type);
}

module_init(my_bus_init);
module_exit(my_bus_exit);

device.c 在sysfs/bus/my_bus/devices目录下创建一个设备my_dev

这里my_dev是一个连接文件，它连接到sysfs/devices/my_bus0/my_dev

#include <linux/device.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/string.h>

MODULE_AUTHOR("David Xie");
MODULE_LICENSE("Dual BSD/GPL");

extern struct device my_bus; 
extern struct bus_type my_bus_type;

/* Why need this ?*/
static void my_dev_release(struct device *dev)
{ 
    
}

struct device my_dev = {
    .bus = &my_bus_type,
    .parent = &my_bus,
    .release = my_dev_release,
};

/*
 * Export a simple attribute.
 */
static ssize_t mydev_show(struct device *dev,struct device_attribute *attr, char *buf)
{
    return sprintf(buf, "%s\n", "This is my device!");
}

static DEVICE_ATTR(dev, S_IRUGO, mydev_show, NULL);

static int __init my_device_init(void)
{
    int ret = 0;
        
        /* 初始化设备 */
    strncpy(my_dev.bus_id, "my_dev", BUS_ID_SIZE);
        
        /*注册设备*/
    device_register(&my_dev);
        
    /*创建属性文件*/
    device_create_file(&my_dev, &dev_attr_dev);
    
    return ret;    

}

static void my_device_exit(void)
{
    device_unregister(&my_dev);
}

module_init(my_device_init);
module_exit(my_device_exit);

driver.c   当加载驱动时候，会在总线上找到它能够处理的设备

#include <linux/device.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/string.h>

MODULE_AUTHOR("David Xie");
MODULE_LICENSE("Dual BSD/GPL");

extern struct bus_type my_bus_type;

static int my_probe(struct device *dev)
{
    printk("Driver found device which my driver can handle!\n");
    return 0;
}

static int my_remove(struct device *dev)
{
    printk("Driver found device unpluged!\n");
    return 0;
}

struct device_driver my_driver = {
    .name = "my_dev",
    .bus = &my_bus_type, /*指明这个驱动程序是属于my_bus_type这条总线上的设备*/
    .probe = my_probe,  /*在my_bus_type总线上找到它能够处理的设备，就调用my_probe;删除设备调用my_remove*/
  .remove    = my_remove,  
  /*能够处理的设备? 
     1、什么时候驱动程序从总线找能够处理的设备；答：驱动注册时候
  2、凭什么说能够处理呢？（或者说标准是什么）；答：驱动与设备都是属于总线上的，利用总线的结构bus_type中match函数
  */
};

/*
 * Export a simple attribute.
 */
static ssize_t mydriver_show(struct device_driver *driver, char *buf)
{
    return sprintf(buf, "%s\n", "This is my driver!");
}

static DRIVER_ATTR(drv, S_IRUGO, mydriver_show, NULL);

static int __init my_driver_init(void)
{
    int ret = 0;
        
  /*注册驱动*/
    driver_register(&my_driver);
        
    /*创建属性文件*/
    driver_create_file(&my_driver, &driver_attr_drv);
    
    return ret;    

}

static void my_driver_exit(void)
{
    driver_unregister(&my_driver);
}

module_init(my_driver_init);
module_exit(my_driver_exit);

注意：无论是先加载驱动还是设备，都会调用probe这个函数。好比先插u盘，在启动系统 与启动系统后再插u盘，系统一样能够支持。