linux驱动篇之 driver_register 过程分析（一）
linux驱动注册过程分析--driver_register（一）
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http://blog.csdn.net/richard_liujh/article/details/45825333
kernel版本3.10.14
driver_register顾名思义，是驱动程序的注册。但是很少是由我们写的驱动直接调用的，例如framebuffer中调用platform_driver_register，i2c中调用i2c_add_driver等等函数注册对应的驱动程序。虽然我们并没有直接调用driver_register，但是最终都是通过driver_register帮我们完成了驱动程序的注册。所以，了解driver_register的注册过程，对我们理解linux的设备驱动有很到的帮助。
我们借助常用的platform_driver_register开始分析driver_register的调用过程。
1.初始化总线类型(bus_type)，注册probe等相关函数
在文件./drivers/base/platform.c中有platform_driver_register源代码：
/**
* platform_driver_register - register a driver for platform-level devices
* @drv: platform driver structure
*/
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;
return driver_register(&drv->driver);
}
EXPORT_SYMBOL_GPL(platform_driver_register);这里我们需要注意，driver的总线类型（bus_type）被初始化为platform_bus_type
drv->driver.bus = &platform_bus_type;struct bus_type platform_bus_type = {
.name = "platform",
.dev_attrs = platform_dev_attrs,
.match = platform_match,
.uevent = platform_uevent,
.pm = &platform_dev_pm_ops,
};其实也类似，例如在./drivers/i2c/i2c-core.c中有I2C注册函数i2c_register_driver源码（省略部分无关代码）
int i2c_register_driver(struct module *owner, struct i2c_driver *driver)
{
……
driver->driver.owner = owner;
driver->driver.bus = &i2c_bus_type;
……
}struct bus_type i2c_bus_type = {
.name = "i2c",
.match = i2c_device_match,
.probe = i2c_device_probe,
.remove = i2c_device_remove,
.shutdown = i2c_device_shutdown,
.pm = &i2c_device_pm_ops,
};当总线类型和probe、remove、shutdown等函数注册后，就开始调用driver_register注册对应的驱动了。
driver_register源代码在文件./drivers/base/driver.c中
/**
* driver_register - register driver with bus
* @drv: driver to register
*
* We pass off most of the work to the bus_add_driver() call,
* since most of the things we have to do deal with the bus
* structures.
*/
int driver_register(struct device_driver *drv)
{
int ret;
struct device_driver *other;
BUG_ON(!drv->bus->p);
if ((drv->bus->probe && drv->probe) ||
(drv->bus->remove && drv->remove) ||
(drv->bus->shutdown && drv->shutdown))
printk(KERN_WARNING "Driver '%s' needs updating - please use "
"bus_type methods\n", drv->name);
other = driver_find(drv->name, drv->bus);
if (other) {
printk(KERN_ERR "Error: Driver '%s' is already registered, "
"aborting...\n", drv->name);
return -EBUSY;
}
ret = bus_add_driver(drv);
if (ret)
return ret;
ret = driver_add_groups(drv, drv->groups);
if (ret) {
bus_remove_driver(drv);
return ret;
}
kobject_uevent(&drv->p->kobj, KOBJ_ADD);
return ret;
}
EXPORT_SYMBOL_GPL(driver_register);int driver_register(struct device_driver *drv)
|
|--> driver_find //查找驱动是否已经装载
|--> bus_add_driver//根据总线类型添加驱动
|--> driver_add_groups//将驱动添加到对应组中
|--> kobject_uevent//注册uevent事件2. driver_find分析
在driver_register中调用driver_find，driver_find名字很通俗易懂，可以简单理解为找“驱动”。由于从linux 2.6版本，内核采用设备驱动模型，所以所谓的“找驱动“还是了解一点设备驱动模型的知识比较好。
在文件./drivers/base/driver.c中有driver_find源码
/**
* driver_find - locate driver on a bus by its name.
* @name: name of the driver.
* @bus: bus to scan for the driver.
*
* Call kset_find_obj() to iterate over list of drivers on
* a bus to find driver by name. Return driver if found.
*
* This routine provides no locking to prevent the driver it returns
* from being unregistered or unloaded while the caller is using it.
* The caller is responsible for preventing this.
*/
struct device_driver *driver_find(const char *name, struct bus_type *bus)
{
struct kobject *k = kset_find_obj(bus->p->drivers_kset, name);
struct driver_private *priv;
if (k) {
/* Drop reference added by kset_find_obj() */
kobject_put(k);
priv = to_driver(k);
return priv->driver;
}
return NULL;
}
EXPORT_SYMBOL_GPL(driver_find);我们注意通过注释和代码知道，driver_find 通过我们给定的name在某bus中寻找驱动。这个比较好理解，就像上学的时候，老师XX知道某个学生的名字（name），然后去他所在的班级（bus）找这个学生。如果找到过（一般没好事TT），就把学生叫出来好好教育一番....。那么driver_find找了所谓的驱动会怎样呢？我们观察driver_find的返回值，你会发现，这里返回的是指针，也就是说driver_find是一个指针函数喽。指针的类型是struct device_driver类型的。
struct device_driver 在文件 include/linux/device.h中定义
/**
* struct device_driver - The basic device driver structure
* @name: Name of the device driver.
* @bus: The bus which the device of this driver belongs to.
* @owner: The module owner.
* @mod_name: Used for built-in modules.
* @suppress_bind_attrs: Disables bind/unbind via sysfs.
* @of_match_table: The open firmware table.
* @acpi_match_table: The ACPI match table.
* @probe: Called to query the existence of a specific device,
* whether this driver can work with it, and bind the driver
* to a specific device.
* @remove: Called when the device is removed from the system to
* unbind a device from this driver.
* @shutdown: Called at shut-down time to quiesce the device.
* @suspend: Called to put the device to sleep mode. Usually to a
* low power state.
* @resume: Called to bring a device from sleep mode.
* @groups: Default attributes that get created by the driver core
* automatically.
* @pm: Power management operations of the device which matched
* this driver.
* @p: Driver core's private data, no one other than the driver
* core can touch this.
*
* The device driver-model tracks all of the drivers known to the system.
* The main reason for this tracking is to enable the driver core to match
* up drivers with new devices. Once drivers are known objects within the
* system, however, a number of other things become possible. Device drivers
* can export information and configuration variables that are independent
* of any specific device.
*/
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;
};/*******************************************************************************************************************************
下面涉及到设备驱动，这里只是简单提一下，一时看不懂很正常。如果有时间还想把设备驱动专门写几篇博文
*******************************************************************************************************************************/
那么问题来了，driver_find到底是如何通过name在bus中寻找驱动呢。其实就是通过下面的代码实现的
struct kobject *k = kset_find_obj(bus->p->drivers_kset, name);所以实现了基本的面向对象管理机制,是构成Linux2.6设备模型的核心结构。它与sysfs文件系统紧密相连,在内核中注册的每个kobject对象对应sysfs文件系统中的一个目录。类似于C++中的基类,Kobject常被嵌入于其他类型(即:容器)中。如bus,devices,drivers都是典型的容器。这些容器通过kobject连接起来,形成了一个树状结构。Bus:在内核中注册的每条总线在该目录下对应一个子目录,如: i2c platform spi ide pci scsi等等 其中每个总线目录内又包含两个子目录:devices和drivers ,devices目录包含了在整个系统中发现的属于该总线类型的设备,drivers目录包含了注册到该总线。其实说这么多，就是想让读者了解一点，我们的driver和bus类型、Kobject，kset等有莫大的关联。至于具体的原理，大家可以自己找一些设备驱动的资料看看。这里就不详细说明了。
在文件./lib/kobject.c 文件中有kset_find_obj函数的源码
* kset_find_obj - search for object in kset.
* @kset: kset we're looking in.
* @name: object's name.
*
* Lock kset via @kset->subsys, and iterate over @kset->list,
* looking for a matching kobject. If matching object is found
* take a reference and return the object.
*/
struct kobject *kset_find_obj(struct kset *kset, const char *name)
{
struct kobject *k;
struct kobject *ret = NULL;
spin_lock(&kset->list_lock);
list_for_each_entry(k, &kset->list, entry) {
if (kobject_name(k) && !strcmp(kobject_name(k), name)) {
ret = kobject_get_unless_zero(k);
break;
}
}
spin_unlock(&kset->list_lock);
return ret;
}总结driver_find过程如下：
1. driver_find，拿到了drv->name和drv->bus开始找驱动
2. kset_find_obj 通过driver_find传递的bus->p->drivers_kset，利用list_for_each_entry遍历kset循环链表。（kset结构体中有循环链表指针next和prev）
3. 遍历循环链表中每一个kobj中的成员变量name
4. 通过strcmp(kobject_name(k), name)比较drv->name 和kobj中的name，如果有相同则表示查找成功
5. return :如果找到，则返回device_driver的指针，如果没有找到则返回了NULL。
为了能更好的说明driver_find，我用下面的图示意一下。
通过下面driver_register的代码可以看出调用driver_find的作用，
other = driver_find(drv->name, drv->bus);
if (other) {
printk(KERN_ERR "Error: Driver '%s' is already registered, "
"aborting...\n", drv->name);
return -EBUSY;
}所以driver_register调用driver_find是为了检验驱动是否已经被注册，防止重复注册。
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