usbcore-generic Framework
理解usbcore-generic framework 的兩個關鍵點是：
- 在此framework中usb driver的註冊、啓動和運轉。
- urb的生命週期和數據流是如何在主機中的class driver/application 和設備端流動的。
urb 傳輸過程
usb_generic_driver
在linux usb系統中有如下對應關係：
usb_device_driver 對應的是usb_device結構，usb_driver對應的是usb_interface結構。
usb_bus_type
struct bus_type usb_bus_type = {
.name = "usb",
.match = usb_device_match,
.uevent = usb_uevent,
};
裏邊的usb_device_match函數用來進行上面圖中所示的對應匹配。
//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的話，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的初始化函數，最後的usb_register_device_driver( )函數註冊了usb_generic_driver, 從上邊match代碼可以看到，usb_generic_driver會匹配所有的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中時，match函數一定返回成功，此時上面的probe函數被調用。
以root hub的啓用爲例，在https://blog.csdn.net/dongkun152/article/details/101377393 中device_add被調用時，整個枚舉過程已經進行完成。此時device已經可用。
下面的代碼參考root hub 啓用文章中建立的數據結構圖。
//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; //獲取該設備配置數組
num_configs = udev->descriptor.bNumConfigurations; //獲得配置數目
for (i = 0; i < num_configs; (i++, c++)) { //選擇配置
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;//獲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; //最佳配置號
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]; //獲取選擇的配置結構
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); //分配配置下的接口結構
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 時將枚舉中獲得的usb_host_endpoint根據方向加入到usb_device中參考https://blog.csdn.net/dongkun152/article/details/101377393 的圖三
//interface 中有struct device,interface 對應的驅動是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);//設置device的名稱準備將其加入到設備模型中
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);//發送set configuration request 到設備啓用選定的配置
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; //啓用的配置
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); //將接口加入到設備模型中，此時會發生與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); //將endpoint加入到設備模型中
}
usb_autosuspend_device(dev);
return 0;
}
EXPORT_SYMBOL_GPL(usb_set_configuration);
創建端點device, 完成後的結構圖見枚舉後半階段 圖四
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 端點名稱以端點地址結尾
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;
}
總結以上整個過程，usb_generic_driver 做了下面幾件事情：
- 匹配新產生的usb_device(此時枚舉已經完成), 選擇一個configuration,向設備發送set configuration request, 使得設備進入configured state.
- 將usb_interface加入到設備模型中，開始usb_driver的匹配，usb_driver的處理從這裏開始。
- 最後將interface下的endpoint 加入到設備模型中。
sys目錄結構
