一、usb_fill_*_urb 函数调用流程
// 控制
static inline void usb_fill_control_urb(struct urb *urb,
struct usb_device *dev,
unsigned int pipe,
unsigned char *setup_packet,
void *transfer_buffer,
int buffer_length,
usb_complete_t complete_fn,
void *context)
// 中断
static inline void usb_fill_int_urb(struct urb *urb,
struct usb_device *dev,
unsigned int pipe,
void *transfer_buffer,
int buffer_length,
usb_complete_t complete_fn,
void *context,
int interval)
// 批量static inline void usb_fill_bulk_urb(struct urb *urb,
struct usb_device *dev,
unsigned int pipe,
void *transfer_buffer,
int buffer_length,
usb_complete_t complete_fn,
void *context)
// 实时
// 实时urb 没有和中断、控制、批量urb 类似的初始化函数，因此它们在提交到USB核心之前，需要在驱动程序中手动的初始化
拿其中的 usb_fill_int_urb 具体分析
static inline void usb_fill_int_urb(struct urb *urb,
struct usb_device *dev,
unsigned int pipe,
void *transfer_buffer,
int buffer_length,
usb_complete_t complete_fn,
void *context,
int interval)
{
urb->dev = dev;
urb->pipe = pipe;
urb->transfer_buffer = transfer_buffer;
urb->transfer_buffer_length = buffer_length;
urb->complete = complete_fn;
urb->context = context;if (dev->speed == USB_SPEED_HIGH || dev->speed >= USB_SPEED_SUPER) {
/* make sure interval is within allowed range */
interval = clamp(interval, 1, 16);urb->interval = 1 << (interval - 1);
} else {
urb->interval = interval;
}urb->start_frame = -1;
}
上面含义就是填充urb 成员，其中的complete_fn 函数，是urb 执行完毕后，usb core 执行的回调函数。
1、urb的complete 执行流程
以usb鼠标驱动为例，具体分析如下：
usb_mouse_probe->
usb_fill_int_urb(mouse->irq, dev, pipe, mouse->data,
(maxp > 8 ? 8 : maxp),
usb_mouse_irq, mouse, endpoint->bInterval); //填充 urb
usb_mouse_irq 为 urb 的complete 函数。
那么urb->complete 执行流程：
usb_mouse_irq <- __usb_hcd_giveback_urb <- usb_giveback_urb_bh
usb_giveback_urb_bh 这个函数是怎么初始化并触发执行？
在增加usb 控制器驱动中，会调用 usb_add_hcd 函数 ，接着，在usb_add_hcd 函数中，会初始化两个软中断：
/* initialize tasklets */
init_giveback_urb_bh(&hcd->high_prio_bh);
init_giveback_urb_bh(&hcd->low_prio_bh);
接着看 init_giveback_urb_bh ：
static void init_giveback_urb_bh(struct giveback_urb_bh *bh)
{spin_lock_init(&bh->lock);
INIT_LIST_HEAD(&bh->head);
tasklet_setup(&bh->bh, usb_giveback_urb_bh);
}
从上面可知，init_giveback_urb_bh 是软中断函数。所以 usb_mouse_irq 是周期性 检测端口是否有鼠标按键的数据到来。
二、usb_submit_urb
usb_submit_urb 调用流程：
usb_submit_urb->
usb_hcd_submit_urb
usb_hcd_submit_urb 函数：
int usb_hcd_submit_urb (struct urb *urb, gfp_t mem_flags)
{
int status;
struct usb_hcd *hcd = bus_to_hcd(urb->dev->bus);/* increment urb's reference count as part of giving it to the HCD
* (which will control it). HCD guarantees that it either returns
* an error or calls giveback(), but not both.
*/
usb_get_urb(urb);
atomic_inc(&urb->use_count);
atomic_inc(&urb->dev->urbnum);
usbmon_urb_submit(&hcd->self, urb);/* NOTE requirements on root-hub callers (usbfs and the hub
* driver, for now): URBs' urb->transfer_buffer must be
* valid and usb_buffer_{sync,unmap}() not be needed, since
* they could clobber root hub response data. Also, control
* URBs must be submitted in process context with interrupts
* enabled.
*/if (is_root_hub(urb->dev)) { -------------------------------------（1）
status = rh_urb_enqueue(hcd, urb);
} else {
status = map_urb_for_dma(hcd, urb, mem_flags);
if (likely(status == 0)) {
status = hcd->driver->urb_enqueue(hcd, urb, mem_flags); -----------（2）
if (unlikely(status))
unmap_urb_for_dma(hcd, urb);
}
}if (unlikely(status)) {
usbmon_urb_submit_error(&hcd->self, urb, status);
urb->hcpriv = NULL;
INIT_LIST_HEAD(&urb->urb_list);
atomic_dec(&urb->use_count);
/*
* Order the write of urb->use_count above before the read
* of urb->reject below. Pairs with the memory barriers in
* usb_kill_urb() and usb_poison_urb().
*/
smp_mb__after_atomic();atomic_dec(&urb->dev->urbnum);
if (atomic_read(&urb->reject))
wake_up(&usb_kill_urb_queue);
usb_put_urb(urb);
}
return status;
}
（1）如果是 root_hub，则调用 rh_urb_enqueue 函数，
static int rh_urb_enqueue (struct usb_hcd *hcd, struct urb *urb)
{
if (usb_endpoint_xfer_int(&urb->ep->desc)) //中断传输
return rh_queue_status (hcd, urb);
if (usb_endpoint_xfer_control(&urb->ep->desc)) //控制传输
return rh_call_control (hcd, urb);
return -EINVAL;
}
共有两个事务。
（2）如果非root_hub ,则调用回调函数urb_enqueue
拿ohci 举例：
static const struct hc_driver ohci_hc_driver = {
.description = hcd_name,
.product_desc = "OHCI Host Controller",
.hcd_priv_size = sizeof(struct ohci_hcd),/*
* generic hardware linkage
*/
.irq = ohci_irq,
.flags = HCD_MEMORY | HCD_DMA | HCD_USB11,/*
* basic lifecycle operations
*/
.reset = ohci_setup,
.start = ohci_start,
.stop = ohci_stop,
.shutdown = ohci_shutdown,/*
* managing i/o requests and associated device resources
*/
.urb_enqueue = ohci_urb_enqueue,
.urb_dequeue = ohci_urb_dequeue,
.endpoint_disable = ohci_endpoint_disable,/*
* scheduling support
*/
.get_frame_number = ohci_get_frame,/*
* root hub support
*/
.hub_status_data = ohci_hub_status_data,
.hub_control = ohci_hub_control,
#ifdef CONFIG_PM
.bus_suspend = ohci_bus_suspend,
.bus_resume = ohci_bus_resume,
#endif
.start_port_reset = ohci_start_port_reset,
};
.urb_enqueue = ohci_urb_enqueue,调用ohci_urb_enqueue 函数，
ohci_urb_enqueue ->td_submit_urb->ohci_writel
留一个问题：ohci 执行完urb 后，如何触发 compelte 函数？目前还未在代码中找到逻辑。