usbcore-generic Framework

usbcore-generic Framework

理解usbcore-generic framework 的两个关键点是：

1. 在此framework中usb driver的注册、启动和运转。
2. urb的生命周期和数据流是如何在主机中的class driver/application 和设备端流动的。

urb 传输过程

usb_generic_driver

在linux usb系统中有如下对应关系：
usb_device_driver 对应的是usb_device结构，usb_driver对应的是usb_interface结构。
usb_bus_type

struct bus_type usb_bus_type = {
	.name =		"usb",
	.match =	usb_device_match,
	.uevent =	usb_uevent,
};

里边的usb_device_match函数用来进行上面图中所示的对应匹配。

//drivers/usb/core/driver.c
static int usb_device_match(struct device *dev, struct device_driver *drv)
{
	/* devices and interfaces are handled separately */
	if (is_usb_device(dev)) {　//如果是usb_devie

		/* interface drivers never match devices */
		if (!is_usb_device_driver(drv)) //如果不是usb_device_driver,不匹配
			return 0;

		/* TODO: Add real matching code */
		return 1; //是usb_device_driver的话，直接匹配

	} else if (is_usb_interface(dev)) {
		struct usb_interface *intf;
		struct usb_driver *usb_drv;
		const struct usb_device_id *id;

		/* device drivers never match interfaces */
		if (is_usb_device_driver(drv))
			return 0;

		intf = to_usb_interface(dev);
		usb_drv = to_usb_driver(drv);

		id = usb_match_id(intf, usb_drv->id_table);
		if (id)
			return 1;

		id = usb_match_dynamic_id(intf, usb_drv);
		if (id)
			return 1;
	}

	return 0;
}

下面是usb system的初始化函数，最后的usb_register_device_driver( )函数注册了usb_generic_driver, 从上边match代码可以看到，usb_generic_driver会匹配所有的usb_device。

//drivers/usb/core/usb.c
/*
 * Init
 */
static int __init usb_init(void)
{
	int retval;
	if (usb_disabled()) {
		pr_info("%s: USB support disabled\n", usbcore_name);
		return 0;
	}
	usb_init_pool_max();

	retval = usb_debugfs_init();
	if (retval)
		goto out;

	usb_acpi_register();
	retval = bus_register(&usb_bus_type);
	if (retval)
		goto bus_register_failed;
	retval = bus_register_notifier(&usb_bus_type, &usb_bus_nb);
	if (retval)
		goto bus_notifier_failed;
	retval = usb_major_init();
	if (retval)
		goto major_init_failed;
	retval = usb_register(&usbfs_driver);
	if (retval)
		goto driver_register_failed;
	retval = usb_devio_init();
	if (retval)
		goto usb_devio_init_failed;
	retval = usb_hub_init();
	if (retval)
		goto hub_init_failed;
	retval = usb_register_device_driver(&usb_generic_driver, THIS_MODULE);
	if (!retval)
		goto out;

	usb_hub_cleanup();
hub_init_failed:
	usb_devio_cleanup();
usb_devio_init_failed:
	usb_deregister(&usbfs_driver);
driver_register_failed:
	usb_major_cleanup();
major_init_failed:
	bus_unregister_notifier(&usb_bus_type, &usb_bus_nb);
bus_notifier_failed:
	bus_unregister(&usb_bus_type);
bus_register_failed:
	usb_acpi_unregister();
	usb_debugfs_cleanup();
out:
	return retval;
}

usb_generic_driver如下

//drivers/usb/core/generic.c
struct usb_device_driver usb_generic_driver = {
	.name =	"usb",
	.probe = generic_probe,
	.disconnect = generic_disconnect,
#ifdef	CONFIG_PM
	.suspend = generic_suspend,
	.resume = generic_resume,
#endif
	.supports_autosuspend = 1,
};

static int generic_probe(struct usb_device *udev)
{
	int err, c;

	/* Choose and set the configuration.  This registers the interfaces
	 * with the driver core and lets interface drivers bind to them.
	 */
	if (udev->authorized == 0)
		dev_err(&udev->dev, "Device is not authorized for usage\n");
	else {
		c = usb_choose_configuration(udev);
		if (c >= 0) {
			err = usb_set_configuration(udev, c);
			if (err && err != -ENODEV) {
				dev_err(&udev->dev, "can't set config #%d, error %d\n",
					c, err);
				/* This need not be fatal.  The user can try to
				 * set other configurations. */
			}
		}
	}
	/* USB device state == configured ... usable */
	usb_notify_add_device(udev);

	return 0;
}

在有usb_device被device_add 加入到usb_bus_type中时，match函数一定返回成功，此时上面的probe函数被调用。
以root hub的启用为例，在https://blog.youkuaiyun.com/dongkun152/article/details/101377393　中device_add被调用时，整个枚举过程已经进行完成。此时device已经可用。
下面的代码参考root hub 启用文章中建立的数据结构图。

//drivers/usb/core/generic.c
int usb_choose_configuration(struct usb_device *udev)
{
	int i;
	int num_configs;
	int insufficient_power = 0;
	struct usb_host_config *c, *best;

	if (usb_device_is_owned(udev))
		return 0;

	best = NULL;
	c = udev->config;　//获取该设备配置数组
	num_configs = udev->descriptor.bNumConfigurations;　//获得配置数目
	for (i = 0; i < num_configs; (i++, c++)) {　//选择配置
		struct usb_interface_descriptor	*desc = NULL;

		/* It's possible that a config has no interfaces! */
		if (c->desc.bNumInterfaces > 0)
			desc = &c->intf_cache[0]->altsetting->desc;//获取配置下的接口描述符

		/*
		 * HP's USB bus-powered keyboard has only one configuration
		 * and it claims to be self-powered; other devices may have
		 * similar errors in their descriptors.  If the next test
		 * were allowed to execute, such configurations would always
		 * be rejected and the devices would not work as expected.
		 * In the meantime, we run the risk of selecting a config
		 * that requires external power at a time when that power
		 * isn't available.  It seems to be the lesser of two evils.
		 *
		 * Bugzilla #6448 reports a device that appears to crash
		 * when it receives a GET_DEVICE_STATUS request!  We don't
		 * have any other way to tell whether a device is self-powered,
		 * but since we don't use that information anywhere but here,
		 * the call has been removed.
		 *
		 * Maybe the GET_DEVICE_STATUS call and the test below can
		 * be reinstated when device firmwares become more reliable.
		 * Don't hold your breath.
		 */
#if 0
		/* Rule out self-powered configs for a bus-powered device */
		if (bus_powered && (c->desc.bmAttributes &
					USB_CONFIG_ATT_SELFPOWER))
			continue;
#endif

		/*
		 * The next test may not be as effective as it should be.
		 * Some hubs have errors in their descriptor, claiming
		 * to be self-powered when they are really bus-powered.
		 * We will overestimate the amount of current such hubs
		 * make available for each port.
		 *
		 * This is a fairly benign sort of failure.  It won't
		 * cause us to reject configurations that we should have
		 * accepted.
		 */

		/* Rule out configs that draw too much bus current */
		if (usb_get_max_power(udev, c) > udev->bus_mA) {
			insufficient_power++;
			continue;
		}

		/* When the first config's first interface is one of Microsoft's
		 * pet nonstandard Ethernet-over-USB protocols, ignore it unless
		 * this kernel has enabled the necessary host side driver.
		 * But: Don't ignore it if it's the only config.
		 */
		if (i == 0 && num_configs > 1 && desc &&
				(is_rndis(desc) || is_activesync(desc))) {
#if !defined(CONFIG_USB_NET_RNDIS_HOST) && !defined(CONFIG_USB_NET_RNDIS_HOST_MODULE)
			continue;
#else
			best = c;
#endif
		}

		/* From the remaining configs, choose the first one whose
		 * first interface is for a non-vendor-specific class.
		 * Reason: Linux is more likely to have a class driver
		 * than a vendor-specific driver. */
		else if (udev->descriptor.bDeviceClass !=
						USB_CLASS_VENDOR_SPEC &&
				(desc && desc->bInterfaceClass !=
						USB_CLASS_VENDOR_SPEC)) {
			best = c;
			break;
		}

		/* If all the remaining configs are vendor-specific,
		 * choose the first one. */
		else if (!best)
			best = c;
	}

	if (insufficient_power > 0)
		dev_info(&udev->dev, "rejected %d configuration%s "
			"due to insufficient available bus power\n",
			insufficient_power, plural(insufficient_power));

	if (best) {
		i = best->desc.bConfigurationValue;　//最佳配置号
		dev_dbg(&udev->dev,
			"configuration #%d chosen from %d choice%s\n",
			i, num_configs, plural(num_configs));
	} else {
		i = -1;
		dev_warn(&udev->dev,
			"no configuration chosen from %d choice%s\n",
			num_configs, plural(num_configs));
	}
	return i;
}
EXPORT_SYMBOL_GPL(usb_choose_configuration);

//drivers/usb/core/message.c
/*
 * usb_set_configuration - Makes a particular device setting be current
 * @dev: the device whose configuration is being updated
 * @configuration: the configuration being chosen.
 * Context: !in_interrupt(), caller owns the device lock
 *
 * This is used to enable non-default device modes.  Not all devices
 * use this kind of configurability; many devices only have one
 * configuration.
 *
 * @configuration is the value of the configuration to be installed.
 * According to the USB spec (e.g. section 9.1.1.5), configuration values
 * must be non-zero; a value of zero indicates that the device in
 * unconfigured.  However some devices erroneously use 0 as one of their
 * configuration values.  To help manage such devices, this routine will
 * accept @configuration = -1 as indicating the device should be put in
 * an unconfigured state.
 *
 * USB device configurations may affect Linux interoperability,
 * power consumption and the functionality available.  For example,
 * the default configuration is limited to using 100mA of bus power,
 * so that when certain device functionality requires more power,
 * and the device is bus powered, that functionality should be in some
 * non-default device configuration.  Other device modes may also be
 * reflected as configuration options, such as whether two ISDN
 * channels are available independently; and choosing between open
 * standard device protocols (like CDC) or proprietary ones.
 *
 * Note that a non-authorized device (dev->authorized == 0) will only
 * be put in unconfigured mode.
 *
 * Note that USB has an additional level of device configurability,
 * associated with interfaces.  That configurability is accessed using
 * usb_set_interface().
 *
 * This call is synchronous. The calling context must be able to sleep,
 * must own the device lock, and must not hold the driver model's USB
 * bus mutex; usb interface driver probe() methods cannot use this routine.
 *
 * Returns zero on success, or else the status code returned by the
 * underlying call that failed.  On successful completion, each interface
 * in the original device configuration has been destroyed, and each one
 * in the new configuration has been probed by all relevant usb device
 * drivers currently known to the kernel.
 */
int usb_set_configuration(struct usb_device *dev, int configuration)
{
	int i, ret;
	struct usb_host_config *cp = NULL;
	struct usb_interface **new_interfaces = NULL;
	struct usb_hcd *hcd = bus_to_hcd(dev->bus);
	int n, nintf;

	if (dev->authorized == 0 || configuration == -1)
		configuration = 0;
	else {
		for (i = 0; i < dev->descriptor.bNumConfigurations; i++) {
			if (dev->config[i].desc.bConfigurationValue ==
					configuration) {
				cp = &dev->config[i];  //获取选择的配置结构
				break;
			}
		}
	}
	if ((!cp && configuration != 0))
		return -EINVAL;

	/* The USB spec says configuration 0 means unconfigured.
	 * But if a device includes a configuration numbered 0,
	 * we will accept it as a correctly configured state.
	 * Use -1 if you really want to unconfigure the device.
	 */
	if (cp && configuration == 0)
		dev_warn(&dev->dev, "config 0 descriptor??\n");

	/* Allocate memory for new interfaces before doing anything else,
	 * so that if we run out then nothing will have changed. */
	n = nintf = 0;
	if (cp) {
		nintf = cp->desc.bNumInterfaces;
		new_interfaces = kmalloc(nintf * sizeof(*new_interfaces),
				GFP_NOIO);
		if (!new_interfaces)
			return -ENOMEM;

		for (; n < nintf; ++n) {
			new_interfaces[n] = kzalloc(
					sizeof(struct usb_interface),
					GFP_NOIO);　//分配配置下的接口结构
			if (!new_interfaces[n]) {
				ret = -ENOMEM;
free_interfaces:
				while (--n >= 0)
					kfree(new_interfaces[n]);
				kfree(new_interfaces);
				return ret;
			}
		}

		i = dev->bus_mA - usb_get_max_power(dev, cp);
		if (i < 0)
			dev_warn(&dev->dev, "new config #%d exceeds power "
					"limit by %dmA\n",
					configuration, -i);
	}

	/* Wake up the device so we can send it the Set-Config request */
	ret = usb_autoresume_device(dev);
	if (ret)
		goto free_interfaces;

	/* if it's already configured, clear out old state first.
	 * getting rid of old interfaces means unbinding their drivers.
	 */
	if (dev->state != USB_STATE_ADDRESS)
		usb_disable_device(dev, 1);	/* Skip ep0 */

	/* Get rid of pending async Set-Config requests for this device */
	cancel_async_set_config(dev);

	/* Make sure we have bandwidth (and available HCD resources) for this
	 * configuration.  Remove endpoints from the schedule if we're dropping
	 * this configuration to set configuration 0.  After this point, the
	 * host controller will not allow submissions to dropped endpoints.  If
	 * this call fails, the device state is unchanged.
	 */
	mutex_lock(hcd->bandwidth_mutex);
	/* Disable LPM, and re-enable it once the new configuration is
	 * installed, so that the xHCI driver can recalculate the U1/U2
	 * timeouts.
	 */
	if (dev->actconfig && usb_disable_lpm(dev)) {
		dev_err(&dev->dev, "%s Failed to disable LPM\n.", __func__);
		mutex_unlock(hcd->bandwidth_mutex);
		ret = -ENOMEM;
		goto free_interfaces;
	}
	ret = usb_hcd_alloc_bandwidth(dev, cp, NULL, NULL);
	if (ret < 0) {
		if (dev->actconfig)
			usb_enable_lpm(dev);
		mutex_unlock(hcd->bandwidth_mutex);
		usb_autosuspend_device(dev);
		goto free_interfaces;
	}

	/*
	 * Initialize the new interface structures and the
	 * hc/hcd/usbcore interface/endpoint state.
	 */
	for (i = 0; i < nintf; ++i) {
		struct usb_interface_cache *intfc;
		struct usb_interface *intf;
		struct usb_host_interface *alt;

		cp->interface[i] = intf = new_interfaces[i];
		intfc = cp->intf_cache[i];
		intf->altsetting = intfc->altsetting;
		intf->num_altsetting = intfc->num_altsetting;
		intf->authorized = !!HCD_INTF_AUTHORIZED(hcd);
		kref_get(&intfc->ref);

		alt = usb_altnum_to_altsetting(intf, 0);

		/* No altsetting 0?  We'll assume the first altsetting.
		 * We could use a GetInterface call, but if a device is
		 * so non-compliant that it doesn't have altsetting 0
		 * then I wouldn't trust its reply anyway.
		 */
		if (!alt)
			alt = &intf->altsetting[0];

		intf->intf_assoc =
			find_iad(dev, cp, alt->desc.bInterfaceNumber);
		intf->cur_altsetting = alt;
		usb_enable_interface(dev, intf, true);//enable 时将枚举中获得的usb_host_endpoint根据方向加入到usb_device中参考https://blog.youkuaiyun.com/dongkun152/article/details/101377393　的图三
		//interface 中有struct device,interface 对应的驱动是usb_driver
		intf->dev.parent = &dev->dev;
		intf->dev.driver = NULL;
		intf->dev.bus = &usb_bus_type;
		intf->dev.type = &usb_if_device_type;
		intf->dev.groups = usb_interface_groups;
		/*
		 * Please refer to usb_alloc_dev() to see why we set
		 * dma_mask and dma_pfn_offset.
		 */
		intf->dev.dma_mask = dev->dev.dma_mask;
		intf->dev.dma_pfn_offset = dev->dev.dma_pfn_offset;
		INIT_WORK(&intf->reset_ws, __usb_queue_reset_device);
		intf->minor = -1;
		device_initialize(&intf->dev);
		pm_runtime_no_callbacks(&intf->dev);
		dev_set_name(&intf->dev, "%d-%s:%d.%d",
			dev->bus->busnum, dev->devpath,
			configuration, alt->desc.bInterfaceNumber);//设置device的名称准备将其加入到设备模型中
		usb_get_dev(dev);
	}
	kfree(new_interfaces);

	ret = usb_control_msg(dev, usb_sndctrlpipe(dev, 0),
			      USB_REQ_SET_CONFIGURATION, 0, configuration, 0,
			      NULL, 0, USB_CTRL_SET_TIMEOUT);//发送set configuration request 到设备启用选定的配置
	if (ret < 0 && cp) {
		/*
		 * All the old state is gone, so what else can we do?
		 * The device is probably useless now anyway.
		 */
		usb_hcd_alloc_bandwidth(dev, NULL, NULL, NULL);
		for (i = 0; i < nintf; ++i) {
			usb_disable_interface(dev, cp->interface[i], true);
			put_device(&cp->interface[i]->dev);
			cp->interface[i] = NULL;
		}
		cp = NULL;
	}

	dev->actconfig = cp;　//启用的配置
	mutex_unlock(hcd->bandwidth_mutex);

	if (!cp) {
		usb_set_device_state(dev, USB_STATE_ADDRESS);

		/* Leave LPM disabled while the device is unconfigured. */
		usb_autosuspend_device(dev);
		return ret;
	}
	usb_set_device_state(dev, USB_STATE_CONFIGURED);

	if (cp->string == NULL &&
			!(dev->quirks & USB_QUIRK_CONFIG_INTF_STRINGS))
		cp->string = usb_cache_string(dev, cp->desc.iConfiguration);

	/* Now that the interfaces are installed, re-enable LPM. */
	usb_unlocked_enable_lpm(dev);
	/* Enable LTM if it was turned off by usb_disable_device. */
	usb_enable_ltm(dev);

	/* Now that all the interfaces are set up, register them
	 * to trigger binding of drivers to interfaces.  probe()
	 * routines may install different altsettings and may
	 * claim() any interfaces not yet bound.  Many class drivers
	 * need that: CDC, audio, video, etc.
	 */
	for (i = 0; i < nintf; ++i) {
		struct usb_interface *intf = cp->interface[i];

		dev_dbg(&dev->dev,
			"adding %s (config #%d, interface %d)\n",
			dev_name(&intf->dev), configuration,
			intf->cur_altsetting->desc.bInterfaceNumber);
		device_enable_async_suspend(&intf->dev);
		ret = device_add(&intf->dev); //将接口加入到设备模型中，此时会发生与usb_driver的匹配和probe
		if (ret != 0) {
			dev_err(&dev->dev, "device_add(%s) --> %d\n",
				dev_name(&intf->dev), ret);
			continue;
		}
		create_intf_ep_devs(intf); //将endpoint加入到设备模型中
	}

	usb_autosuspend_device(dev);
	return 0;
}
EXPORT_SYMBOL_GPL(usb_set_configuration);

创建端点device, 完成后的结构图见枚举后半阶段　图四

static int create_intf_ep_devs(struct usb_interface *intf)
{
	struct usb_device *udev = interface_to_usbdev(intf);
	struct usb_host_interface *alt = intf->cur_altsetting;
	int i;

	if (intf->ep_devs_created || intf->unregistering)
		return 0;

	for (i = 0; i < alt->desc.bNumEndpoints; ++i)
		(void) usb_create_ep_devs(&intf->dev, &alt->endpoint[i], udev);
	intf->ep_devs_created = 1;
	return 0;
}
int usb_create_ep_devs(struct device *parent,
			struct usb_host_endpoint *endpoint,
			struct usb_device *udev)
{
	struct ep_device *ep_dev;
	int retval;

	ep_dev = kzalloc(sizeof(*ep_dev), GFP_KERNEL);
	if (!ep_dev) {
		retval = -ENOMEM;
		goto exit;
	}

	ep_dev->desc = &endpoint->desc;
	ep_dev->udev = udev;
	ep_dev->dev.groups = ep_dev_groups;
	ep_dev->dev.type = &usb_ep_device_type;
	ep_dev->dev.parent = parent;
	dev_set_name(&ep_dev->dev, "ep_%02x", endpoint->desc.bEndpointAddress);//endpoint 端点名称以端点地址结尾

	retval = device_register(&ep_dev->dev);
	if (retval)
		goto error_register;

	device_enable_async_suspend(&ep_dev->dev);
	endpoint->ep_dev = ep_dev;
	return retval;

error_register:
	put_device(&ep_dev->dev);
exit:
	return retval;
}

总结以上整个过程，usb_generic_driver 做了下面几件事情：

1. 匹配新产生的usb_device(此时枚举已经完成), 选择一个configuration,向设备发送set configuration request, 使得设备进入configured state.
2. 将usb_interface加入到设备模型中，开始usb_driver的匹配，usb_driver的处理从这里开始。
3. 最后将interface下的endpoint 加入到设备模型中。

sys目录结构