LINUX设备驱动之设备模型五--device&driver&bus（三）

uthor: Eric Fang

Date: 2010-01-18
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本站分析linux内核源码，版本号为2.6.32.3
转载请注明出处：http://ericfang.cublog.cn/
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接上一篇文章，继续device_add()中的代码：
error = bus_add_device(dev);
if (error)
goto BusError;
在对应总线目录下的device目录下创建几个到device的链接文件。
error = dpm_sysfs_add(dev);
if (error)
goto DPMError;
device_pm_add(dev);
添加power文件。
/* Notify clients of device addition. This call must come
* after dpm_sysf_add() and before kobject_uevent().
*/
if (dev->bus)
blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
BUS_NOTIFY_ADD_DEVICE, dev);
调用bus的回调函数。
kobject_uevent(&dev->kobj, KOBJ_ADD);
产生一个add事件。
bus_probe_device(dev);
这个函数将匹配已经注册到总线的驱动程序，如下：
void bus_probe_device(struct device *dev)
{
struct bus_type *bus = dev->bus;
int ret;

if (bus && bus->p->drivers_autoprobe) {
ret = device_attach(dev);
WARN_ON(ret < 0);
}
}
只有bus->p->drivers_autoprobe设置为1是才会去匹配，device_attach()如下：
int device_attach(struct device *dev)
{
int ret = 0;

down(&dev->sem);
if (dev->driver) {
ret = device_bind_driver(dev);
if (ret == 0)
ret = 1;
else {
dev->driver = NULL;
ret = 0;
}
} else {
pm_runtime_get_noresume(dev);
ret = bus_for_each_drv(dev->bus, NULL, dev, __device_attach);
pm_runtime_put_sync(dev);
}
up(&dev->sem);
return ret;
}
如果已指定了dev->driver，则直接在相应的driver目录下建立链接文件，将驱动和设备绑定。
int device_bind_driver(struct device *dev)
{
int ret;

ret = driver_sysfs_add(dev);
if (!ret)
driver_bound(dev);
return ret;
}
driver_bound()函数如下：
static void driver_bound(struct device *dev)
{
if (klist_node_attached(&dev->p->knode_driver)) {
printk(KERN_WARNING "%s: device %s already bound/n",
__func__, kobject_name(&dev->kobj));
return;
}

pr_debug("driver: '%s': %s: bound to device '%s'/n", dev_name(dev),
__func__, dev->driver->name);

if (dev->bus)
blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
BUS_NOTIFY_BOUND_DRIVER, dev);

klist_add_tail(&dev->p->knode_driver, &dev->driver->p->klist_devices);
}
通知总线绑定驱动，将设备添加到驱动的设备链表。
否则调用bus_for_each_drv()匹配总线上的驱动：
int bus_for_each_drv(struct bus_type *bus, struct device_driver *start,
void *data, int (*fn)(struct device_driver *, void *))
{
struct klist_iter i;
struct device_driver *drv;
int error = 0;

if (!bus)
return -EINVAL;

klist_iter_init_node(&bus->p->klist_drivers, &i,
start ? &start->p->knode_bus : NULL);
while ((drv = next_driver(&i)) && !error)
error = fn(drv, data);
klist_iter_exit(&i);
return error;
}
历遍总线上的驱动，每次都调用回调函数fn()（这里是__device_attach），如果fn()返回1则匹配成功，__device_attach()如下：
static int __device_attach(struct device_driver *drv, void *data)
{
struct device *dev = data;

if (!driver_match_device(drv, dev))
return 0;

return driver_probe_device(drv, dev);
}
driver_match_device()如下：
static inline int driver_match_device(struct device_driver *drv,
struct device *dev)
{
return drv->bus->match ? drv->bus ->match(dev, drv) : 1;
}
用drv->bus的match方法进行匹配，如果成功就会继续调用driver_probe_device()：
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;
}
进行一下验证和同步后调用really_probe()最终详细的匹配：
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) {
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;
}
先假定dev的驱动为drv，然后如果总线闪的probe存在，则调用它，否则调用drv的probe（）函数，返回0则匹配成功，调用driver_bound()进行设备和驱动的绑定。driver_bound()函数在上面已经分析。

接着device_add()函数中的代码：
if (dev->class) {
mutex_lock(&dev->class->p->class_mutex);
/* tie the class to the device */
klist_add_tail(&dev->knode_class,
&dev->class->p->class_devices);

/* notify any interfaces that the device is here */
list_for_each_entry(class_intf,
&dev->class->p->class_interfaces, node)
if (class_intf->add_dev)
class_intf->add_dev(dev, class_intf);
mutex_unlock(&dev->class->p->class_mutex);
}
Dev所属class的一些操作。
done:
put_device(dev);
return error;
DPMError:
bus_remove_device(dev);
BusError:
device_remove_attrs(dev);
AttrsError:
device_remove_class_symlinks(dev);
SymlinkError:
if (MAJOR(dev->devt))
device_remove_sys_dev_entry(dev);
devtattrError:
if (MAJOR(dev->devt))
device_remove_file(dev, &devt_attr);
ueventattrError:
device_remove_file(dev, &uevent_attr);
attrError:
kobject_uevent(&dev->kobj, KOBJ_REMOVE);
kobject_del(&dev->kobj);
Error:
cleanup_device_parent(dev);
if (parent)
put_device(parent);
name_error:
kfree(dev->p);
dev->p = NULL;
goto done;
最后是一下除错撤销处理。
}
至此，已经详细的分析了创建和注册设备的函数。
内核撤销设备注册的函数为device_unregister()，这里不再分析。

内核提供注册驱动的函数为driver_register()：
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);
验证driver的包含了需要的方法，并打印信息。
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;
}
如果驱动已注册则返回-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;
}
bus_add_driver()代码如下：
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);
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;
}
简单的分析一下： 为drv分配内存并初始化，创建文件系统中相应的目录、属性文件和链接，调用driver_attach()匹配总线上的设备，将驱动注册到bus上，产生一个 kobject_uevent() ADD事件。详细的过程请参考内核源码。
同样内核提供driver_unregister()函数撤销驱动注册，这里不再分析。

至此，已经清楚了设备驱动模型的device、driver和bus，在此基础上就可以轻松的去分析各个模块的驱动程序了^_^!