linux powerpc i2c驱动 之 i2c设备层的注册过程

 

Linux下i2c驱动的加载过程，分为i2c设备层、i2c adapter层与i2c核心层

i2c设备驱动层也就是我们为特定i2c设备编写的驱动，下面是我自己理解的i2c驱动的注册过程

在我们写的i2c设备驱动中，我们会调用i2c_add_driver()开始i2c设备驱动的注册，该函数调用i2c_register_driver完成所有注册操作

 

 

static inline int i2c_add_driver(struct i2c_driver *driver)
{
return i2c_register_driver(THIS_MODULE, driver);
}

i2c_register_driver会调用driver_register() 来将设备驱动添加到总线的设备驱动链表中：

int i2c_register_driver(struct module *owner, struct i2c_driver *driver)
{
int res;
/* Can't register until after driver model init */
if (unlikely(WARN_ON(!i2c_bus_type.p)))
return -EAGAIN;
driver->driver.owner = owner;
driver->driver.bus = &i2c_bus_type;
/* When registration returns, the driver core
 * will have called probe() for all matching-but-unbound devices.
 */
res = driver_register(&driver->driver);
if (res)
return res;
pr_debug("i2c-core: driver [%s] registered\n", driver->driver.name);
INIT_LIST_HEAD(&driver->clients);
/* Walk the adapters that are already present */
mutex_lock(&core_lock);
bus_for_each_dev(&i2c_bus_type, NULL, driver, __attach_adapter);
mutex_unlock(&core_lock);
return 0;
}

在driver_register中，通过driver_find来判断驱动是否已经注册，然后会调用

bus_add_drive

将设备驱动添加到总线上

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) {
put_driver(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;
}

在bus_add_driver中初始化priv->klist_devices的值，并将priv赋值给drv->p

通过调用klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers)将驱动信息保存到总线结构中，在此之前将调用driver_attach()

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);
if (error)
goto out_unregister;
if (drv->bus->p->drivers_autoprobe) {
error = driver_attach(drv);
if (error)
goto out_unregister;
}
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:
kfree(drv->p);
drv->p = NULL;
kobject_put(&priv->kobj);
out_put_bus:
bus_put(bus);
return error;
}

在driver_attach中，通过调用bus_for_each_dev，遍历在总线上挂载的所有设备，并对每个设备(dev)调用__driver_attach()

int driver_attach(struct device_driver *drv)
{
return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach);
}

在__driver_attach里会调用driver_match_device()来判断dev与driv的id是否相同，在i2c驱动里就会调用i2c_bus_type->match程序进行判断，

当id相同时，将会调用driver_probe_device()

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))
return 0;
if (dev->parent) /* Needed for USB */
down(&dev->parent->sem);
down(&dev->sem);
if (!dev->driver)
driver_probe_device(drv, dev);
up(&dev->sem);
if (dev->parent)
up(&dev->parent->sem);
return 0;
}

在driver_probe_device(),首先会调用device_is_registered()判断dev是否注册，若没注册则返回；若已经注册，则调用really_probe

int driver_probe_device(struct device_driver *drv, struct device *dev)
{
int ret = 0;
if (!device_is_registered(dev))
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);
pm_runtime_put_sync(dev);
return ret;
}

在really_probe()里，首先将drv赋值给dev->driver，然后会调用总线的probe函数，在i2c驱动里，

此时将会调用i2c总线的probe函数：i2c_device_probe

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;
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) 
{
//此处调用i2c总线的probe函数
ret = dev->bus->probe(dev);
if (ret)
goto probe_failed;
} 
else if (drv->probe) 
{
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 != -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);
}
/* * 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;
}

在i2c_device_probe()里，会根据to_i2c_driver(dev->driver)获取i2c驱动，也就是我们编写的具体的i2c设备驱动的结构体i2c_driver，即

static struct i2c_driver XXX_driver = {
.driver = {
.name = "XXXX_name",
.owner = THIS_MODULE,
},
.probe = XXX_probe,
.remove = XXX_remove,
.id_table = XXX_id,
};

这样就调用了我们驱动的probe()了，这就是我们在驱动里调用i2c_add_driver()，通过driver_register()的一系列调用，最后执行我们所写的probe()

static int i2c_device_probe(struct device *dev)
{
struct i2c_client *client = i2c_verify_client(dev);
struct i2c_driver *driver;
int status;
if (!client)
return 0;
driver = to_i2c_driver(dev->driver);
if (!driver->probe || !driver->id_table)
return -ENODEV;
client->driver = driver;
if (!device_can_wakeup(&client->dev))
device_init_wakeup(&client->dev,
client->flags & I2C_CLIENT_WAKE);
dev_dbg(dev, "probe\n");
status = driver->probe(client, i2c_match_id(driver->id_table, client));//执行我们写的probe函数
if (status)
client->driver = NULL;
return status;
}