在上一篇文章中分析了,i2c设备和i2c驱动的向总线注册过程。在总线-设备-驱动这种模型中,无论是先进行driver_register还是后进行device_register,总线驱动都会对进行匹配,只有匹配工程后,才会执行驱动的probe函数;
首先分析driver_register函数,先看此函数源码(driver/base/driver.c):
int driver_register(struct device_driver *drv)
{
int ret;
struct device_driver *other;
BUG_ON(!drv->bus->p);
/*检查总线上注册的函数和driver注册的函数是否一样*/
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);
/*查找总线上是否注册了这个设备驱动,此函数见分析1*/
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);//向bus中添加此设备驱动程序,下面详细分析此函数,见2
if (ret)
return ret;
ret = driver_add_groups(drv, drv->groups);
if (ret)
bus_remove_driver(drv);
return ret;
}
**1.**driver_find源码如下:
struct device_driver *driver_find(const char *name, struct bus_type *bus)
{
/*这里涉及到kobj和kset的概念,将bus的kset传入函数kset_find_obj,kset是一个结构体,结构体里有链表这一成员,链表里面记录着这类kobjet,通过比较object的成员变量name和传进来的name是否相等,来判断是否注册过此类设备。kset_find_obj函数就不向下跟了,有兴趣可参考https://blog.csdn.net/tmkeepgood/article/details/8767408*/
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;
}
**2.**bus_add_driver源码如下:
int bus_add_driver(struct device_driver *drv)
{
struct bus_type *bus;
struct driver_private *priv;
int error = 0;
bus = bus_get(drv->bus);
if (!bus)
return -EINVAL;
pr_debug("bus: '%s': add driver %s\n", bus->name, drv->name);
priv = kzalloc(sizeof(*priv), GFP_KERNEL);
if (!priv) {
error = -ENOMEM;
goto out_put_bus;
}
klist_init(&priv->klist_devices, NULL, NULL);
priv->driver = drv;
drv->p = priv;
priv->kobj.kset = bus->p->drivers_kset;
error = kobject_init_and_add(&priv->kobj, &driver_ktype, NULL,
"%s", drv->name);
/*初始化并添加kobject,就是在sys/bus/i2c/driver目录下新建此驱动对应的目录*/
if (error)
goto out_unregister;
if (drv->bus->p->drivers_autoprobe) {
error = driver_attach(drv);//匹配函数,下面重点分析。
if (error)
goto out_unregister;
}
/*一旦匹配成功,下面的函数就是为上面kobject_init_and_add函数建立的驱动文件添加相应的属性*/
klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers);
module_add_driver(drv->owner, drv);
error = driver_create_file(drv, &driver_attr_uevent);
if (error) {
printk(KERN_ERR "%s: uevent attr (%s) failed\n",
__func__, drv->name);
}
error = driver_add_attrs(bus, drv);
if (error) {
/* How the hell do we get out of this pickle? Give up */
printk(KERN_ERR "%s: driver_add_attrs(%s) failed\n",
__func__, drv->name);
}
if (!drv->suppress_bind_attrs) {
error = add_bind_files(drv);
if (error) {
/* Ditto */
printk(KERN_ERR "%s: add_bind_files(%s) failed\n",
__func__, drv->name);
}
}
kobject_uevent(&priv->kobj, KOBJ_ADD);
return 0;
out_unregister:
kobject_put(&priv->kobj);
kfree(drv->p);
drv->p = NULL;
out_put_bus:
bus_put(bus);
return error;
}
下面主要看driver_attach函数,此函数是driver主动去匹配device,源码如下(driver/base/dd.c):
int driver_attach(struct device_driver *drv)
{
return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach);//调用此函数,这里的__driver_attach是一个函数指针,传递给bus_for_each_dev函数
}
函数bus_for_each_dev源码如下(driver/base/bus.c):
int bus_for_each_dev(struct bus_type *bus, struct device *start,
void *data, int (*fn)(struct device *, void *))
{
struct klist_iter i;
struct device *dev;
int error = 0;
if (!bus || !bus->p)
return -EINVAL;
klist_iter_init_node(&bus->p->klist_devices, &i,
(start ? &start->p->knode_bus : NULL));//遍历这个链表上的所有设备
while ((dev = next_device(&i)) && !error)
/*这里调用next_device,类似于之前分析的next_driver,
拿出设备链表中的每一个设备,
将dirver和device传递给fn,即__driver_attach*/
error = fn(dev, data);
klist_iter_exit(&i);
return error;
}
下面看__driver_attach源码,看其是怎么样匹配设备和驱动的(driver/base/dd.c):
static int __driver_attach(struct device *dev, void *data)
{
struct device_driver *drv = data;
/*
* Lock device and try to bind to it. We drop the error
* here and always return 0, because we need to keep trying
* to bind to devices and some drivers will return an error
* simply if it didn't support the device.
*
* driver_probe_device() will spit a warning if there
* is an error.
*/
if (!driver_match_device(drv, dev))//匹配设备和驱动,详见2.1
return 0;
if (dev->parent) /* Needed for USB */
device_lock(dev->parent);
device_lock(dev);
if (!dev->driver)
driver_probe_device(drv, dev);//匹配成功以后调用此函数,详见2.2
device_unlock(dev);
if (dev->parent)
device_unlock(dev->parent);
return 0;
}
2.1下面看driver_match_device源码(driver/base/base.h):
static inline int driver_match_device(struct device_driver *drv,
struct device *dev)
{
return drv->bus->match ? drv->bus->match(dev, drv) : 1;
/*如果注册了bus的match函数,就调用bus的match函数,没有则返回1
这个bus的match在哪里注册的呢?是在i2c_register_driver函数中注册的
i2c_register_driver函数中这条程序driver->driver.bus = &i2c_bus_type;
对bus进行了注册,i2c_bus_type源码如下:
struct bus_type i2c_bus_type = {
.name = "i2c",
.match = i2c_device_match,//这些函数在i2c_register_driver都有定义
.probe = i2c_device_probe,
.remove = i2c_device_remove,
.shutdown = i2c_device_shutdown,
.pm = &i2c_device_pm_ops,
};
*/
}//这是一个内联函数,只能定义在头文件中
下面看i2c_device_match的源码(driver/i2c/i2c-core.c):
static int i2c_device_match(struct device *dev, struct device_driver *drv)
{
struct i2c_client *client = i2c_verify_client(dev);
struct i2c_driver *driver;
if (!client)
return 0;
/* Attempt an OF style match */
/*这个函数是也是进行dev和drv的匹配,当平台使用设备树来记录硬件信息时,
会调用此函数进行匹配,使用设备树时drv和dev匹配的依据是.compatible这一属性*/
if (of_driver_match_device(dev, drv))
return 1;
driver = to_i2c_driver(drv);
/* match on an id table if there is one */
if (driver->id_table)
return i2c_match_id(driver->id_table, client) != NULL;
/*当平台使用i2c_board_info结构体来记录板级信息时,使用此函数进行drv和dev的匹配,两种匹配的依据是dev的name和drv的id_table,下面继续分析这种方法的匹配*/
return 0;
}
下面看i2c_match_id函数的源码:
static const struct i2c_device_id *i2c_match_id(const struct i2c_device_id *id,
const struct i2c_client *client)
{
while (id->name[0]) {
if (strcmp(client->name, id->name) == 0)//比较client和drv中id_table是否相同
return id;
id++;
}
return NULL;
}
2.2无论是使用of_driver_match_device(设备树)函数进行匹配还是使用i2c_match_id(结构体记录板级信息)函数进行匹配,匹配成功时都会调用driver_probe_device函数。下面看这个函数源码,看其实怎么调用设备驱动中的probe函数的(driver/base/dd.c):
nt driver_probe_device(struct device_driver *drv, struct device *dev)
{
int ret = 0;
if (!device_is_registered(dev))//判断这个设备是否已经注册
return -ENODEV;
pr_debug("bus: '%s': %s: matched device %s with driver %s\n",
drv->bus->name, __func__, dev_name(dev), drv->name);
pm_runtime_get_noresume(dev);
pm_runtime_barrier(dev);
ret = really_probe(dev, drv);//在调用此函数
pm_runtime_put_sync(dev);
return ret;
}
看really_probe函数源码:
static int really_probe(struct device *dev, struct device_driver *drv)
{
int ret = 0;
atomic_inc(&probe_count);
pr_debug("bus: '%s': %s: probing driver %s with device %s\n",
drv->bus->name, __func__, drv->name, dev_name(dev));
WARN_ON(!list_empty(&dev->devres_head));
dev->driver = drv;
/*driver_sysfs_add函数就是建立sys/bus/i2c/driver下的驱动
与sys/bus/i2c/devicec下设备的链接*/
if (driver_sysfs_add(dev)) {
printk(KERN_ERR "%s: driver_sysfs_add(%s) failed\n",
__func__, dev_name(dev));
goto probe_failed;
}
if (dev->bus->probe) {//先调用驱动总线的probe函数
ret = dev->bus->probe(dev);
if (ret)
goto probe_failed;
} else if (drv->probe) {
//再调用自己driver的probe函数。执行到这就是已经调用驱动程序中的probe函数了
ret = drv->probe(dev);
if (ret)
goto probe_failed;
}
driver_bound(dev);
ret = 1;
pr_debug("bus: '%s': %s: bound device %s to driver %s\n",
drv->bus->name, __func__, dev_name(dev), drv->name);
goto done;
probe_failed:
devres_release_all(dev);
driver_sysfs_remove(dev);
dev->driver = NULL;
if (ret == -EPROBE_DEFER) {
/* Driver requested deferred probing */
dev_info(dev, "Driver %s requests probe deferral\n", drv->name);
driver_deferred_probe_add(dev);
} else if (ret != -ENODEV && ret != -ENXIO) {
/* driver matched but the probe failed */
printk(KERN_WARNING
"%s: probe of %s failed with error %d\n",
drv->name, dev_name(dev), ret);
} else {
pr_debug("%s: probe of %s rejects match %d\n",
drv->name, dev_name(dev), ret);
}
/*
* Ignore errors returned by ->probe so that the next driver can try
* its luck.
*/
ret = 0;
done:
atomic_dec(&probe_count);
wake_up(&probe_waitqueue);
return ret;
}