1 概念

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struct device_driver {
	const char		*name;
	const struct bus_type	*bus; // 必须指定 bus_type

	struct module		*owner;
	const char		*mod_name;	/* used for built-in modules */

	bool suppress_bind_attrs;	/* disables bind/unbind via sysfs */
	enum probe_type probe_type;

	const struct of_device_id	*of_match_table;
	const struct acpi_device_id	*acpi_match_table;

	int (*probe) (struct device *dev);
	void (*sync_state)(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 attribute_group **dev_groups;

	const struct dev_pm_ops *pm;
	void (*coredump) (struct device *dev);

	struct driver_private *p;
};

2 接口

driver_register() 能够注册驱动到 bus.

在 /sys/bus/<bus>/drivers/<driver_name>/ 下创建一个目录.

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struct device_driver {
    const char *name;
    struct bus_type *bus;   /* 驱动必须依附在哪条 bus 上 */
    ...
};

注册的核心是 bus_add_driver() 将驱动装载到 bus 上，因此 bus 必须存在.

在 driver_register() 的过程中还会将 device 和 driver 进行 match，但是如果上面没有 device 也不会出错，后期注册 device 就行了.

因此 device 和 driver 的注册没有先后关系.

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int driver_register(struct device_driver *drv)
{
	int ret;
	struct device_driver *other;

	if (!bus_is_registered(drv->bus)) {
		pr_err("Driver '%s' was unable to register with bus_type '%s' because the bus was not initialized.\n",
			   drv->name, drv->bus->name);
		return -EINVAL;
	}

	if ((drv->bus->probe && drv->probe) ||
	    (drv->bus->remove && drv->remove) ||
	    (drv->bus->shutdown && drv->shutdown))
		pr_warn("Driver '%s' needs updating - please use "
			"bus_type methods\n", drv->name);

	other = driver_find(drv->name, drv->bus);
	if (other) {
		pr_err("Error: Driver '%s' is already registered, "
			"aborting...\n", drv->name);
		return -EBUSY;
	}

	ret = bus_add_driver(drv); // 将驱动添加到总线
	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); // 通知内核，驱动注册成功了
	deferred_probe_extend_timeout();

	return ret;
}

那么我们看是如何将 bus 和 driver 进行绑定的.

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int bus_add_driver(struct device_driver *drv)
{
	struct subsys_private *sp = bus_to_subsys(drv->bus);
	struct driver_private *priv;
	int error = 0;

	if (!sp)
		return -EINVAL;

	/*
	 * Reference in sp is now incremented and will be dropped when
	 * the driver is removed from the bus
	 */
	pr_debug("bus: '%s': add driver %s\n", sp->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 = sp->drivers_kset;
	error = kobject_init_and_add(&priv->kobj, &driver_ktype, NULL,
				     "%s", drv->name);
	if (error)
		goto out_unregister;

	klist_add_tail(&priv->knode_bus, &sp->klist_drivers);
	if (sp->drivers_autoprobe) {
        // 将 driver 和 device 绑定
		error = driver_attach(drv);
		if (error)
			goto out_del_list;
	}
	error = module_add_driver(drv->owner, drv);
	if (error) {
		printk(KERN_ERR "%s: failed to create module links for %s\n",
			__func__, drv->name);
		goto out_detach;
	}

    // /sys/bus/<bus_name>/drivers/<driver_name>/uevent
	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_groups(drv, sp->bus->drv_groups);
	if (error) {
		/* How the hell do we get out of this pickle? Give up */
		printk(KERN_ERR "%s: driver_add_groups(%s) failed\n",
			__func__, drv->name);
	}

	if (!drv->suppress_bind_attrs) {
        // /sys/bus/<bus_name>/drivers/<driver_name>/bind
        // /sys/bus/<bus_name>/drivers/<driver_name>/unbind
		error = add_bind_files(drv);
		if (error) {
			/* Ditto */
			printk(KERN_ERR "%s: add_bind_files(%s) failed\n",
				__func__, drv->name);
		}
	}

	return 0;

out_detach:
	driver_detach(drv);
out_del_list:
	klist_del(&priv->knode_bus);
out_unregister:
	kobject_put(&priv->kobj);
	/* drv->p is freed in driver_release()  */
	drv->p = NULL;
out_put_bus:
	subsys_put(sp);
	return error;
}

上面我们看到我们还要将 driver 和 device 进行绑定.

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int driver_attach(const struct device_driver *drv)
{
	/* The (void *) will be put back to const * in __driver_attach() */
	return bus_for_each_dev(drv->bus, NULL, (void *)drv, __driver_attach);
}

实际上执行 __driver_attach 来尝试将 bus 上的 device 和 driver 进行绑定.

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static int __driver_attach(struct device *dev, void *data)
{
	const struct device_driver *drv = data;
	bool async = false;
	int ret;

	/*
	 * 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.
	 */

	ret = driver_match_device(drv, dev); // 将驱动程序和设备进行绑定检测
	if (ret == 0) {
		/* no match */
		return 0;
	} else if (ret == -EPROBE_DEFER) {
		dev_dbg(dev, "Device match requests probe deferral\n");
		dev->can_match = true;
		driver_deferred_probe_add(dev);
		/*
		 * Driver could not match with device, but may match with
		 * another device on the bus.
		 */
		return 0;
	} else if (ret < 0) {
		dev_dbg(dev, "Bus failed to match device: %d\n", ret);
		/*
		 * Driver could not match with device, but may match with
		 * another device on the bus.
		 */
		return 0;
	} /* ret > 0 means positive match */

	if (driver_allows_async_probing(drv)) {
		/*
		 * Instead of probing the device synchronously we will
		 * probe it asynchronously to allow for more parallelism.
		 *
		 * We only take the device lock here in order to guarantee
		 * that the dev->driver and async_driver fields are protected
		 */
		dev_dbg(dev, "probing driver %s asynchronously\n", drv->name);
		device_lock(dev);
		if (!dev->driver && !dev->p->async_driver) {
			get_device(dev);
			dev->p->async_driver = drv;
			async = true;
		}
		device_unlock(dev);
		if (async)
			async_schedule_dev(__driver_attach_async_helper, dev);
		return 0;
	}

	__device_driver_lock(dev, dev->parent);
	driver_probe_device(drv, dev); // 将驱动程序和设备进行绑定检测
	__device_driver_unlock(dev, dev->parent);

	return 0;
}