一般是上层的功能驱动程序通过该函数想core提交urb,core会转递给控制器,控制器处理完urb后,会调用urb的回调函数,将urb控制权重新交给功能驱动程序。驱动程序会重新提交或者释放urb:
int usb_submit_urb(struct urb *urb, gfp_t mem_flags) { int xfertype, max; struct usb_device *dev; struct usb_host_endpoint *ep; int is_out; if (!urb || urb->hcpriv || !urb->complete) return -EINVAL; dev = urb->dev; if ((!dev) || (dev->state < USB_STATE_UNAUTHENTICATED)) return -ENODEV; /* For now, get the endpoint from the pipe. Eventually drivers * will be required to set urb->ep directly and we will eliminate * urb->pipe. */ ep = usb_pipe_endpoint(dev, urb->pipe); if (!ep) return -ENOENT; urb->ep = ep; urb->status = -EINPROGRESS; urb->actual_length = 0; /* Lots of sanity checks, so HCDs can rely on clean data * and don't need to duplicate tests */ xfertype = usb_endpoint_type(&ep->desc); if (xfertype == USB_ENDPOINT_XFER_CONTROL) { struct usb_ctrlrequest *setup = (struct usb_ctrlrequest *) urb->setup_packet; if (!setup) return -ENOEXEC; is_out = !(setup->bRequestType & USB_DIR_IN) || !setup->wLength; } else { is_out = usb_endpoint_dir_out(&ep->desc); } /* Clear the internal flags and cache the direction for later use */ urb->transfer_flags &= ~(URB_DIR_MASK | URB_DMA_MAP_SINGLE | URB_DMA_MAP_PAGE | URB_DMA_MAP_SG | URB_MAP_LOCAL | URB_SETUP_MAP_SINGLE | URB_SETUP_MAP_LOCAL | URB_DMA_SG_COMBINED); urb->transfer_flags |= (is_out ? URB_DIR_OUT : URB_DIR_IN); if (xfertype != USB_ENDPOINT_XFER_CONTROL && dev->state < USB_STATE_CONFIGURED) return -ENODEV; max = le16_to_cpu(ep->desc.wMaxPacketSize); if (max <= 0) { dev_dbg(&dev->dev, "bogus endpoint ep%d%s in %s (bad maxpacket %d)\n", usb_endpoint_num(&ep->desc), is_out ? "out" : "in", __func__, max); return -EMSGSIZE; } /* periodic transfers limit size per frame/uframe, * but drivers only control those sizes for ISO. * while we're checking, initialize return status. */ if (xfertype == USB_ENDPOINT_XFER_ISOC) { int n, len; /* SuperSpeed isoc endpoints have up to 16 bursts of up to * 3 packets each */ if (dev->speed == USB_SPEED_SUPER) { int burst = 1 + ep->ss_ep_comp.bMaxBurst; int mult = USB_SS_MULT(ep->ss_ep_comp.bmAttributes); max *= burst; max *= mult; } /* "high bandwidth" mode, 1-3 packets/uframe? */ if (dev->speed == USB_SPEED_HIGH) { int mult = 1 + ((max >> 11) & 0x03); max &= 0x07ff; max *= mult; } if (urb->number_of_packets <= 0) return -EINVAL; for (n = 0; n < urb->number_of_packets; n++) { len = urb->iso_frame_desc[n].length; if (len < 0 || len > max) return -EMSGSIZE; urb->iso_frame_desc[n].status = -EXDEV; urb->iso_frame_desc[n].actual_length = 0; } } /* the I/O buffer must be mapped/unmapped, except when length=0 */ if (urb->transfer_buffer_length > INT_MAX) return -EMSGSIZE; #ifdef DEBUG /* stuff that drivers shouldn't do, but which shouldn't * cause problems in HCDs if they get it wrong. */ { unsigned int orig_flags = urb->transfer_flags; unsigned int allowed; static int pipetypes[4] = { PIPE_CONTROL, PIPE_ISOCHRONOUS, PIPE_BULK, PIPE_INTERRUPT }; /* Check that the pipe's type matches the endpoint's type */ if (usb_pipetype(urb->pipe) != pipetypes[xfertype]) { dev_err(&dev->dev, "BOGUS urb xfer, pipe %x != type %x\n", usb_pipetype(urb->pipe), pipetypes[xfertype]); return -EPIPE; /* The most suitable error code */ } /* enforce simple/standard policy */ allowed = (URB_NO_TRANSFER_DMA_MAP | URB_NO_INTERRUPT | URB_DIR_MASK | URB_FREE_BUFFER); switch (xfertype) { case USB_ENDPOINT_XFER_BULK: if (is_out) allowed |= URB_ZERO_PACKET; /* FALLTHROUGH */ case USB_ENDPOINT_XFER_CONTROL: allowed |= URB_NO_FSBR; /* only affects UHCI */ /* FALLTHROUGH */ default: /* all non-iso endpoints */ if (!is_out) allowed |= URB_SHORT_NOT_OK; break; case USB_ENDPOINT_XFER_ISOC: allowed |= URB_ISO_ASAP; break; } urb->transfer_flags &= allowed; /* fail if submitter gave bogus flags */ if (urb->transfer_flags != orig_flags) { dev_err(&dev->dev, "BOGUS urb flags, %x --> %x\n", orig_flags, urb->transfer_flags); return -EINVAL; } } #endif /* * Force periodic transfer intervals to be legal values that are * a power of two (so HCDs don't need to). * * FIXME want bus->{intr,iso}_sched_horizon values here. Each HC * supports different values... this uses EHCI/UHCI defaults (and * EHCI can use smaller non-default values). */ switch (xfertype) { case USB_ENDPOINT_XFER_ISOC: case USB_ENDPOINT_XFER_INT: /* too small? */ switch (dev->speed) { case USB_SPEED_WIRELESS: if (urb->interval < 6) return -EINVAL; break; default: if (urb->interval <= 0) return -EINVAL; break; } /* too big? */ switch (dev->speed) { case USB_SPEED_SUPER: /* units are 125us */ /* Handle up to 2^(16-1) microframes */ if (urb->interval > (1 << 15)) return -EINVAL; max = 1 << 15; break; case USB_SPEED_WIRELESS: if (urb->interval > 16) return -EINVAL; break; case USB_SPEED_HIGH: /* units are microframes */ /* NOTE usb handles 2^15 */ if (urb->interval > (1024 * 8)) urb->interval = 1024 * 8; max = 1024 * 8; break; case USB_SPEED_FULL: /* units are frames/msec */ case USB_SPEED_LOW: if (xfertype == USB_ENDPOINT_XFER_INT) { if (urb->interval > 255) return -EINVAL; /* NOTE ohci only handles up to 32 */ max = 128; } else { if (urb->interval > 1024) urb->interval = 1024; /* NOTE usb and ohci handle up to 2^15 */ max = 1024; } break; default: return -EINVAL; } if (dev->speed != USB_SPEED_WIRELESS) { /* Round down to a power of 2, no more than max */ urb->interval = min(max, 1 << ilog2(urb->interval)); } } return usb_hcd_submit_urb(urb, mem_flags); }
usb_submit_urb首先会对urb进行一些设置,然后调用主机控制器函数usb_hcd_submit_urb来完成递交操作。在usb_hcd_submit_urb函数中,如果设备为root hub,则调用rh_urb_enqueue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)) { 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); 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); atomic_dec(&urb->dev->urbnum); if (atomic_read(&urb->reject)) wake_up(&usb_kill_urb_queue); usb_put_urb(urb); } return status; }
在rh_urb_enqueue函数中,主要对hub的urb进行排队:
static int rh_urb_enqueue (struct usb_hcd *hcd, struct urb *urb) { if (usb_endpoint_xfer_int(&urb->ep->desc)) return rh_queue_status (hcd, urb); if (usb_endpoint_xfer_control(&urb->ep->desc)) return rh_call_control (hcd, urb); return -EINVAL; }
若不是root hub 则调用注册的驱动函数:hcd->driver->urb_enqueue(hcd, urb, mem_flags);
针对不同的控制器,会跳转到不同的struct hc_driver注册时的实现函数:urb_enqueue
总之,urb的生命周期从申请创建开始,到驱动程序中的填充,将urb分配给usb设备指定的端点,需要数据通信往端点写数据时,调用usb_submit_urb函数提交到usb core,usb core再进行一些处理就转递给主机控制器的驱动程序HCD,HCD就会解析这个urb,了解它的目的是什么,并与usb设备进行相应的交流,将数据发往usb设备。发送完成,交流结束,urb的目的达到之后,usb控制器驱动会执行urb的回调函数,通知usb功能驱动程序,并将这个urb的控制权回交给功能驱动程序。