【打卡】【sysfs相关API详解】21天学习挑战赛—RK3399平台开发入门到精通-Day20

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在Linux概念中，bus下还细化很多，比如不仅仅真正的物理总线归类为bus，还有常用的platform虚拟总线，接下来看看详细的platform总线的相关platform_bus_init：
kernel/drivers/base/platform.c

struct bus_type platform_bus_type = {
    .name       = "platform",  // 总线类型名称
    .dev_groups = platform_dev_groups, //总线设备组，包括设备属性
    .match      = platform_match, //总线匹配函数
    .uevent     = platform_uevent, //热拔插操作函数
    .pm     = &platform_dev_pm_ops, //电源管理，休眠唤醒操作集
};
EXPORT_SYMBOL_GPL(platform_bus_type);

int __init platform_bus_init(void)
{
    int error;

    early_platform_cleanup();

    error = device_register(&platform_bus); //总线也是设备，也要进行设备注册
    if (error)
        return error;
    error =  bus_register(&platform_bus_type); // 注册platform_bus_type总线到内核
    if (error)
        device_unregister(&platform_bus);
    of_platform_register_reconfig_notifier();
    return error;
}

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尽管上面的bus
因为device和driver都是挂载在bus上的，为层次结构清晰，接下来按照顺序看看详细的bus_register、device_register和bus_register的实现机制：

bus_register

kernel/drivers/base/bus.c

/**
 * bus_register - register a driver-core subsystem
 * @bus: bus to register
 *
 * Once we have that, we register the bus with the kobject
 * infrastructure, then register the children subsystems it has:
 * the devices and drivers that belong to the subsystem.
 */
int bus_register(struct bus_type *bus)
{
    int retval;
    struct subsys_private *priv;
    struct lock_class_key *key = &bus->lock_key;

    priv = kzalloc(sizeof(struct subsys_private), GFP_KERNEL);
    if (!priv)
        return -ENOMEM;

    priv->bus = bus;
    bus->p = priv;

    BLOCKING_INIT_NOTIFIER_HEAD(&priv->bus_notifier);

    retval = kobject_set_name(&priv->subsys.kobj, "%s", bus->name);
    if (retval)
        goto out;

    priv->subsys.kobj.kset = bus_kset;
    priv->subsys.kobj.ktype = &bus_ktype;
    priv->drivers_autoprobe = 1;

    retval = kset_register(&priv->subsys);
    if (retval)
        goto out;

    retval = bus_create_file(bus, &bus_attr_uevent);
    if (retval)
        goto bus_uevent_fail;

    priv->devices_kset = kset_create_and_add("devices", NULL,
                         &priv->subsys.kobj);
    if (!priv->devices_kset) {
        retval = -ENOMEM;
        goto bus_devices_fail;
    }

    priv->drivers_kset = kset_create_and_add("drivers", NULL,
                         &priv->subsys.kobj);
    if (!priv->drivers_kset) {
        retval = -ENOMEM;
        goto bus_drivers_fail;
    }

    INIT_LIST_HEAD(&priv->interfaces);
    __mutex_init(&priv->mutex, "subsys mutex", key);
    klist_init(&priv->klist_devices, klist_devices_get, klist_devices_put);
    klist_init(&priv->klist_drivers, NULL, NULL);

    retval = add_probe_files(bus);
    if (retval)
        goto bus_probe_files_fail;

    retval = bus_add_groups(bus, bus->bus_groups);
    if (retval)
        goto bus_groups_fail;

    pr_debug("bus: '%s': registered\n", bus->name);
    return 0;

bus_groups_fail:
    remove_probe_files(bus);
bus_probe_files_fail:
    kset_unregister(bus->p->drivers_kset);
bus_drivers_fail:
    kset_unregister(bus->p->devices_kset);
bus_devices_fail:
    bus_remove_file(bus, &bus_attr_uevent);
bus_uevent_fail:
    kset_unregister(&bus->p->subsys);
out:
    kfree(bus->p);
    bus->p = NULL;
    return retval;
}
EXPORT_SYMBOL_GPL(bus_register);

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通过bus_register注册完bus后，将会生成目录结构如下：