USB EHCI Driver_ehci_poll_ass

USB EHCI Driver

struct echi_hcd

struct ehci_hcd {			/* one per controller */
	/* timing support */
	enum ehci_hrtimer_event	next_hrtimer_event;
	unsigned		enabled_hrtimer_events;
	ktime_t			hr_timeouts[EHCI_HRTIMER_NUM_EVENTS];
	struct hrtimer		hrtimer;

	int			PSS_poll_count;
	int			ASS_poll_count;
	int			died_poll_count;

	/* glue to PCI and HCD framework */
	struct ehci_caps __iomem *caps;
	struct ehci_regs __iomem *regs;
	struct ehci_dbg_port __iomem *debug;

	__u32			hcs_params;	/* cached register copy */
	spinlock_t		lock;
	enum ehci_rh_state	rh_state;

	/* general schedule support */
	bool			scanning:1;
	bool			need_rescan:1;
	bool			intr_unlinking:1;
	bool			iaa_in_progress:1;
	bool			async_unlinking:1;
	bool			shutdown:1;
	struct ehci_qh		*qh_scan_next;

	/* async schedule support */
	struct ehci_qh		*async;
	struct ehci_qh		*dummy;		/* For AMD quirk use */
	struct list_head	async_unlink;
	struct list_head	async_idle;
	unsigned		async_unlink_cycle;
	unsigned		async_count;	/* async activity count */
	__hc32			old_current;	/* Test for QH becoming */
	__hc32			old_token;	/*  inactive during unlink */

	/* periodic schedule support */
#define	DEFAULT_I_TDPS		1024		/* some HCs can do less */
	unsigned		periodic_size;
	__hc32			*periodic;	/* hw periodic table */
	dma_addr_t		periodic_dma;
	struct list_head	intr_qh_list;
	unsigned		i_thresh;	/* uframes HC might cache */

	union ehci_shadow	*pshadow;	/* mirror hw periodic table */
	struct list_head	intr_unlink_wait;
	struct list_head	intr_unlink;
	unsigned		intr_unlink_wait_cycle;
	unsigned		intr_unlink_cycle;
	unsigned		now_frame;	/* frame from HC hardware */
	unsigned		last_iso_frame;	/* last frame scanned for iso */
	unsigned		intr_count;	/* intr activity count */
	unsigned		isoc_count;	/* isoc activity count */
	unsigned		periodic_count;	/* periodic activity count */
	unsigned		uframe_periodic_max; /* max periodic time per uframe */


	/* list of itds & sitds completed while now_frame was still active */
	struct list_head	cached_itd_list;
	struct ehci_itd		*last_itd_to_free;
	struct list_head	cached_sitd_list;
	struct ehci_sitd	*last_sitd_to_free;

	/* per root hub port */
	unsigned long		reset_done[EHCI_MAX_ROOT_PORTS];//记录已经reset的port

	/* bit vectors (one bit per port) */
	unsigned long		bus_suspended;		/* which ports were
			already suspended at the start of a bus suspend */
	unsigned long		companion_ports;	/* which ports are
			dedicated to the companion controller */
	unsigned long		owned_ports;		/* which ports are
			owned by the companion during a bus suspend */
	unsigned long		port_c_suspend;		/* which ports have
			the change-suspend feature turned on */
	unsigned long		suspended_ports;	/* which ports are
			suspended */
	unsigned long		resuming_ports;		/* which ports have
			started to resume */

	/* per-HC memory pools (could be per-bus, but ...) */
	struct dma_pool		*qh_pool;	/* qh per active urb */
	struct dma_pool		*qtd_pool;	/* one or more per qh */
	struct dma_pool		*itd_pool;	/* itd per iso urb */
	struct dma_pool		*sitd_pool;	/* sitd per split iso urb */

	unsigned		random_frame;
	unsigned long		next_statechange;
	ktime_t			last_periodic_enable;
	u32			command;

	/* SILICON QUIRKS */
	unsigned		no_selective_suspend:1;
	unsigned		has_fsl_port_bug:1; /* FreeScale */
	unsigned		has_fsl_hs_errata:1;	/* Freescale HS quirk */
	unsigned		big_endian_mmio:1;
	unsigned		big_endian_desc:1;
	unsigned		big_endian_capbase:1;
	unsigned		has_amcc_usb23:1;
	unsigned		need_io_watchdog:1;
	unsigned		amd_pll_fix:1;
	unsigned		use_dummy_qh:1;	/* AMD Frame List table quirk*/
	unsigned		has_synopsys_hc_bug:1; /* Synopsys HC */
	unsigned		frame_index_bug:1; /* MosChip (AKA NetMos) */
	unsigned		need_oc_pp_cycle:1; /* MPC834X port power */
	unsigned		imx28_write_fix:1; /* For Freescale i.MX28 */

	/* required for usb32 quirk */
	#define OHCI_CTRL_HCFS          (3 << 6)
	#define OHCI_USB_OPER           (2 << 6)
	#define OHCI_USB_SUSPEND        (3 << 6)

	#define OHCI_HCCTRL_OFFSET      0x4
	#define OHCI_HCCTRL_LEN         0x4
	__hc32			*ohci_hcctrl_reg;
	unsigned		has_hostpc:1;
	unsigned		has_tdi_phy_lpm:1;
	unsigned		has_ppcd:1; /* support per-port change bits */
	u8			sbrn;		/* packed release number */

	/* irq statistics */
#ifdef EHCI_STATS
	struct ehci_stats	stats;
#	define COUNT(x) ((x)++)
#else
#	define COUNT(x)
#endif

	/* debug files */
#ifdef CONFIG_DYNAMIC_DEBUG
	struct dentry		*debug_dir;
#endif

	/* bandwidth usage */
#define EHCI_BANDWIDTH_SIZE	64
#define EHCI_BANDWIDTH_FRAMES	(EHCI_BANDWIDTH_SIZE >> 3)
	u8			bandwidth[EHCI_BANDWIDTH_SIZE];
						/* us allocated per uframe */
	u8			tt_budget[EHCI_BANDWIDTH_SIZE];
						/* us budgeted per uframe */
	struct list_head	tt_list;

	/* platform-specific data -- must come last */
	unsigned long		priv[0] __aligned(sizeof(s64));
};


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struct urb

/**
 * struct urb - USB Request Block
 * @urb_list: For use by current owner of the URB.
 * @anchor_list: membership in the list of an anchor
 * @anchor: to anchor URBs to a common mooring
 * @ep: Points to the endpoint's data structure.  Will eventually
 *	replace @pipe.
 * @pipe: Holds endpoint number, direction, type, and more.
 *	Create these values with the eight macros available;
 *	usb_{snd,rcv}TYPEpipe(dev,endpoint), where the TYPE is "ctrl"
 *	(control), "bulk", "int" (interrupt), or "iso" (isochronous).
 *	For example usb_sndbulkpipe() or usb_rcvintpipe().  Endpoint
 *	numbers range from zero to fifteen.  Note that "in" endpoint two
 *	is a different endpoint (and pipe) from "out" endpoint two.
 *	The current configuration controls the existence, type, and
 *	maximum packet size of any given endpoint.
 * @stream_id: the endpoint's stream ID for bulk streams
 * @dev: Identifies the USB device to perform the request.
 * @status: This is read in non-iso completion functions to get the
 *	status of the particular request.  ISO requests only use it
 *	to tell whether the URB was unlinked; detailed status for
 *	each frame is in the fields of the iso_frame-desc.
 * @transfer_flags: A variety of flags may be used to affect how URB
 *	submission, unlinking, or operation are handled.  Different
 *	kinds of URB can use different flags.
 * @transfer_buffer:  This identifies the buffer to (or from) which the I/O
 *	request will be performed unless URB_NO_TRANSFER_DMA_MAP is set
 *	(however, do not leave garbage in transfer_buffer even then).
 *	This buffer must be suitable for DMA; allocate it with
 *	kmalloc() or equivalent.  For transfers to "in" endpoints, contents
 *	of this buffer will be modified.  This buffer is used for the data
 *	stage of control transfers.
 * @transfer_dma: When transfer_flags includes URB_NO_TRANSFER_DMA_MAP,
 *	the device driver is saying that it provided this DMA address,
 *	which the host controller driver should use in preference to the
 *	transfer_buffer.
 * @sg: scatter gather buffer list, the buffer size of each element in
 * 	the list (except the last) must be divisible by the endpoint's
 * 	max packet size if no_sg_constraint isn't set in 'struct usb_bus'
 * @num_mapped_sgs: (internal) number of mapped sg entries
 * @num_sgs: number of entries in the sg list
 * @transfer_buffer_length: How big is transfer_buffer.  The transfer may
 *	be broken up into chunks according to the current maximum packet
 *	size for the endpoint, which is a function of the configuration
 *	and is encoded in the pipe.  When the length is zero, neither
 *	transfer_buffer nor transfer_dma is used.
 * @actual_length: This is read in non-iso completion functions, and
 *	it tells how many bytes (out of transfer_buffer_length) were
 *	transferred.  It will normally be the same as requested, unless
 *	either an error was reported or a short read was performed.
 *	The URB_SHORT_NOT_OK transfer flag may be used to make such
 *	short reads be reported as errors.
 * @setup_packet: Only used for control transfers, this points to eight bytes
 *	of setup data.  Control transfers always start by sending this data
 *	to the device.  Then transfer_buffer is read or written, if needed.
 * @setup_dma: DMA pointer for the setup packet.  The caller must not use
 *	this field; setup_packet must point to a valid buffer.
 * @start_frame: Returns the initial frame for isochronous transfers.
 * @number_of_packets: Lists the number of ISO transfer buffers.
 * @interval: Specifies the polling interval for interrupt or isochronous
 *	transfers.  The units are frames (milliseconds) for full and low
 *	speed devices, and microframes (1/8 millisecond) for highspeed
 *	and SuperSpeed devices.
 * @error_count: Returns the number of ISO transfers that reported errors.
 * @context: For use in completion functions.  This normally points to
 *	request-specific driver context.
 * @complete: Completion handler. This URB is passed as the parameter to the
 *	completion function.  The completion function may then do what
 *	it likes with the URB, including resubmitting or freeing it.
 * @iso_frame_desc: Used to provide arrays of ISO transfer buffers and to
 *	collect the transfer status for each buffer.
 *
 * This structure identifies USB transfer requests.  URBs must be allocated by
 * calling usb_alloc_urb() and freed with a call to usb_free_urb().
 * Initialization may be done using various usb_fill_*_urb() functions.  URBs
 * are submitted using usb_submit_urb(), and pending requests may be canceled
 * using usb_unlink_urb() or usb_kill_urb().
 *
 * Data Transfer Buffers:
 *
 * Normally drivers provide I/O buffers allocated with kmalloc() or otherwise
 * taken from the general page pool.  That is provided by transfer_buffer
 * (control requests also use setup_packet), and host controller drivers
 * perform a dma mapping (and unmapping) for each buffer transferred.  Those
 * mapping operations can be expensive on some platforms (perhaps using a dma
 * bounce buffer or talking to an IOMMU),
 * although they're cheap on commodity x86 and ppc hardware.
 *
 * Alternatively, drivers may pass the URB_NO_TRANSFER_DMA_MAP transfer flag,
 * which tells the host controller driver that no such mapping is needed for
 * the transfer_buffer since
 * the device driver is DMA-aware.  For example, a device driver might
 * allocate a DMA buffer with usb_alloc_coherent() or call usb_buffer_map().
 * When this transfer flag is provided, host controller drivers will
 * attempt to use the dma address found in the transfer_dma
 * field rather than determining a dma address themselves.
 *
 * Note that transfer_buffer must still be set if the controller
 * does not support DMA (as indicated by bus.uses_dma) and when talking
 * to root hub. If you have to trasfer between highmem zone and the device
 * on such controller, create a bounce buffer or bail out with an error.
 * If transfer_buffer cannot be set (is in highmem) and the controller is DMA
 * capable, assign NULL to it, so that usbmon knows not to use the value.
 * The setup_packet must always be set, so it cannot be located in highmem.
 *
 * Initialization:
 *
 * All URBs submitted must initialize the dev, pipe, transfer_flags (may be
 * zero), and complete fields.  All URBs must also initialize
 * transfer_buffer and transfer_buffer_length.  They may provide the
 * URB_SHORT_NOT_OK transfer flag, indicating that short reads are
 * to be treated as errors; that flag is invalid for write requests.
 *
 * Bulk URBs may
 * use the URB_ZERO_PACKET transfer flag, indicating that bulk OUT transfers
 * should always terminate with a short packet, even if it means adding an
 * extra zero length packet.
 *
 * Control URBs must provide a valid pointer in the setup_packet field.
 * Unlike the transfer_buffer, the setup_packet may not be mapped for DMA
 * beforehand.
 *
 * Interrupt URBs must provide an interval, saying how often (in milliseconds
 * or, for highspeed devices, 125 microsecond units)
 * to poll for transfers.  After the URB has been submitted, the interval
 * field reflects how the transfer was actually scheduled.
 * The polling interval may be more frequent than requested.
 * For example, some controllers have a maximum interval of 32 milliseconds,
 * while others support intervals of up to 1024 milliseconds.
 * Isochronous URBs also have transfer intervals.  (Note that for isochronous
 * endpoints, as well as high speed interrupt endpoints, the encoding of
 * the transfer interval in the endpoint descriptor is logarithmic.
 * Device drivers must convert that value to linear units themselves.)
 *
 * If an isochronous endpoint queue isn't already running, the host
 * controller will schedule a new URB to start as soon as bandwidth
 * utilization allows.  If the queue is running then a new URB will be
 * scheduled to start in the first transfer slot following the end of the
 * preceding URB, if that slot has not already expired.  If the slot has
 * expired (which can happen when IRQ delivery is delayed for a long time),
 * the scheduling behavior depends on the URB_ISO_ASAP flag.  If the flag
 * is clear then the URB will be scheduled to start in the expired slot,
 * implying that some of its packets will not be transferred; if the flag
 * is set then the URB will be scheduled in the first unexpired slot,
 * breaking the queue's synchronization.  Upon URB completion, the
 * start_frame field will be set to the (micro)frame number in which the
 * transfer was scheduled.  Ranges for frame counter values are HC-specific
 * and can go from as low as 256 to as high as 65536 frames.
 *
 * Isochronous URBs have a different data transfer model, in part because
 * the quality of service is only "best effort".  Callers provide specially
 * allocated URBs, with number_of_packets worth of iso_frame_desc structures
 * at the end.  Each such packet is an individual ISO transfer.  Isochronous
 * URBs are normally queued, submitted by drivers to arrange that
 * transfers are at least double buffered, and then explicitly resubmitted
 * in completion handlers, so
 * that data (such as audio or video) streams at as constant a rate as the
 * host controller scheduler can support.
 *
 * Completion Callbacks:
 *
 * The completion callback is made in_interrupt(), and one of the first
 * things that a completion handler should do is check the status field.
 * The status field is provided for all URBs.  It is used to report
 * unlinked URBs, and status for all non-ISO transfers.  It should not
 * be examined before the URB is returned to the completion handler.
 *
 * The context field is normally used to link URBs back to the relevant
 * driver or request state.
 *
 * When the completion callback is invoked for non-isochronous URBs, the
 * actual_length field tells how many bytes were transferred.  This field
 * is updated even when the URB terminated with an error or was unlinked.
 *
 * ISO transfer status is reported in the status and actual_length fields
 * of the iso_frame_desc array, and the number of errors is reported in
 * error_count.  Completion callbacks for ISO transfers will normally
 * (re)submit URBs to ensure a constant transfer rate.
 *
 * Note that even fields marked "public" should not be touched by the driver
 * when the urb is owned by the hcd, that is, since the call to
 * usb_submit_urb() till the entry into the completion routine.
 */
struct urb {
	/* private: usb core and host controller only fields in the urb */
	struct kref kref;		/* reference count of the URB */
	void *hcpriv;			/* private data for host controller */
	atomic_t use_count;		/* concurrent submissions counter */
	atomic_t reject;		/* submissions will fail */
	int unlinked;			/* unlink error code */

	/* public: documented fields in the urb that can be used by drivers */
	struct list_head urb_list;	/* list head for use by the urb's
					 * current owner */
	struct list_head anchor_list;	/* the URB may be anchored */
	struct usb_anchor *anchor;
	struct usb_device *dev;		/* (in) pointer to associated device */
	struct usb_host_endpoint *ep;	/* (internal) pointer to endpoint */
	unsigned int pipe;		/* (in) pipe information */
	unsigned int stream_id;		/* (in) stream ID */
	int status;			/* (return) non-ISO status */
	unsigned int transfer_flags;	/* (in) URB_SHORT_NOT_OK | ...*/
	void *transfer_buffer;		/* (in) associated data buffer */
	dma_addr_t transfer_dma;	/* (in) dma addr for transfer_buffer */
	struct scatterlist *sg;		/* (in) scatter gather buffer list */
	int num_mapped_sgs;		/* (internal) mapped sg entries */
	int num_sgs;			/* (in) number of entries in the sg list */
	u32 transfer_buffer_length;	/* (in) data buffer length */
	u32 actual_length;		/* (return) actual transfer length */
	unsigned char *setup_packet;	/* (in) setup packet (control only) */
	dma_addr_t setup_dma;		/* (in) dma addr for setup_packet */
	int start_frame;		/* (modify) start frame (ISO) */
	int number_of_packets;		/* (in) number of ISO packets */
	int interval;			/* (modify) transfer interval
					 * (INT/ISO) */
	int error_count;		/* (return) number of ISO errors */
	void *context;			/* (in) context for completion */
	usb_complete_t complete;	/* (in) completion routine */
	struct usb_iso_packet_descriptor iso_frame_desc[0];
					/* (in) ISO ONLY */
};

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在usb_hcd_submit_urb中会区分是root hub还是usb 设备，如下代码

/*-------------------------------------------------------------------------*/

/* may be called in any context with a valid urb->dev usecount
 * caller surrenders "ownership" of urb
 * expects usb_submit_urb() to have sanity checked and conditioned all
 * inputs in the urb
 */
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)) {　//如果是root hub
		status = rh_urb_enqueue(hcd, urb);
	} else { // 不是root hub
		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;
}

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rh_urb_enqueue()当中分为两部分，端点0的控制传输，端点１的中断传输。

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;
}
static int rh_queue_status (struct usb_hcd *hcd, struct urb *urb)
{
	int		retval;
	unsigned long	flags;
	unsigned	len = 1 + (urb->dev->maxchild / 8);

	spin_lock_irqsave (&hcd_root_hub_lock, flags);
	if (hcd->status_urb || urb->transfer_buffer_length < len) {
		dev_dbg (hcd->self.controller, "not queuing rh status urb\n");
		retval = -EINVAL;
		goto done;
	}

	retval = usb_hcd_link_urb_to_ep(hcd, urb);
	if (retval)
		goto done;

	hcd->status_urb = urb;
	urb->hcpriv = hcd;	/* indicate it's queued */
	if (!hcd->uses_new_polling)
		mod_timer(&hcd->rh_timer, (jiffies/(HZ/4) + 1) * (HZ/4));

	/* If a status change has already occurred, report it ASAP */
	else if (HCD_POLL_PENDING(hcd))
		mod_timer(&hcd->rh_timer, jiffies);
	retval = 0;
 done:
	spin_unlock_irqrestore (&hcd_root_hub_lock, flags);
	return retval;
}
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rh_timer_func是rh_timer的回调函数。

/* timer callback */
static void rh_timer_func (unsigned long _hcd)
{
	usb_hcd_poll_rh_status((struct usb_hcd *) _hcd);
}

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ehci driver 如下

static const struct hc_driver ehci_hc_driver = {
	.description =		hcd_name,
	.product_desc =		"EHCI Host Controller",
	.hcd_priv_size =	sizeof(struct ehci_hcd),

	/*
	 * generic hardware linkage
	 */
	.irq =			ehci_irq,
	.flags =		HCD_MEMORY | HCD_USB2 | HCD_BH,

	/*
	 * basic lifecycle operations
	 */
	.reset =		ehci_setup,
	.start =		ehci_run,
	.stop =			ehci_stop,
	.shutdown =		ehci_shutdown,

	/*
	 * managing i/o requests and associated device resources
	 */
	.urb_enqueue =		ehci_urb_enqueue,
	.urb_dequeue =		ehci_urb_dequeue,
	.endpoint_disable =	ehci_endpoint_disable,
	.endpoint_reset =	ehci_endpoint_reset,
	.clear_tt_buffer_complete =	ehci_clear_tt_buffer_complete,

	/*
	 * scheduling support
	 */
	.get_frame_number =	ehci_get_frame,

	/*
	 * root hub support
	 */
	.hub_status_data =	ehci_hub_status_data,
	.hub_control =		ehci_hub_control,
	.bus_suspend =		ehci_bus_suspend,
	.bus_resume =		ehci_bus_resume,
	.relinquish_port =	ehci_relinquish_port,
	.port_handed_over =	ehci_port_handed_over,

	/*
	 * device support
	 */
	.free_dev =		ehci_remove_device,
};

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/*-------------------------------------------------------------------------*/

/*
 * non-error returns are a promise to giveback() the urb later
 * we drop ownership so next owner (or urb unlink) can get it
 *
 * urb + dev is in hcd.self.controller.urb_list
 * we're queueing TDs onto software and hardware lists
 *
 * hcd-specific init for hcpriv hasn't been done yet
 *
 * NOTE:  control, bulk, and interrupt share the same code to append TDs
 * to a (possibly active) QH, and the same QH scanning code.
 */
static int ehci_urb_enqueue (
	struct usb_hcd	*hcd,
	struct urb	*urb,
	gfp_t		mem_flags
) {
	struct ehci_hcd		*ehci = hcd_to_ehci (hcd);
	struct list_head	qtd_list;

	INIT_LIST_HEAD (&qtd_list);

	switch (usb_pipetype (urb->pipe)) {
	case PIPE_CONTROL:　//控制传输
		/* qh_completions() code doesn't handle all the fault cases
		 * in multi-TD control transfers.  Even 1KB is rare anyway.
		 */
		if (urb->transfer_buffer_length > (16 * 1024))
			return -EMSGSIZE;
		/* FALLTHROUGH */
	/* case PIPE_BULK: */
	default:　//块传输　控制传输和块传输用一个传输函数
		if (!qh_urb_transaction (ehci, urb, &qtd_list, mem_flags))　//将urb
			return -ENOMEM;
		return submit_async(ehci, urb, &qtd_list, mem_flags);

	case PIPE_INTERRUPT:　//中断传输
		if (!qh_urb_transaction (ehci, urb, &qtd_list, mem_flags))
			return -ENOMEM;
		return intr_submit(ehci, urb, &qtd_list, mem_flags);

	case PIPE_ISOCHRONOUS:　//同步传输
		if (urb->dev->speed == USB_SPEED_HIGH)
			return itd_submit (ehci, urb, mem_flags);
		else
			return sitd_submit (ehci, urb, mem_flags);
	}
}

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在提交到硬件进行数据处理时，会出现很多缩写，如果不清楚这些缩写，看函数的时候都会一脸蒙。缩写的意思可以从ehci_reg的解释中找到。

struct ehci_regs {

	/* USBCMD: offset 0x00 */
	u32		command;

/* EHCI 1.1 addendum */
#define CMD_HIRD	(0xf<<24)	/* host initiated resume duration */
#define CMD_PPCEE	(1<<15)		/* per port change event enable */
#define CMD_FSP		(1<<14)		/* fully synchronized prefetch */
#define CMD_ASPE	(1<<13)		/* async schedule prefetch enable */
#define CMD_PSPE	(1<<12)		/* periodic schedule prefetch enable */
/* 23:16 is r/w intr rate, in microframes; default "8" == 1/msec */
#define CMD_PARK	(1<<11)		/* enable "park" on async qh */
#define CMD_PARK_CNT(c)	(((c)>>8)&3)	/* how many transfers to park for */
#define CMD_LRESET	(1<<7)		/* partial reset (no ports, etc) */
#define CMD_IAAD	(1<<6)		/* "doorbell" interrupt async advance */
#define CMD_ASE		(1<<5)		/* async schedule enable */
#define CMD_PSE		(1<<4)		/* periodic schedule enable */
/* 3:2 is periodic frame list size */
#define CMD_RESET	(1<<1)		/* reset HC not bus */
#define CMD_RUN		(1<<0)		/* start/stop HC */

	/* USBSTS: offset 0x04 */
	u32		status;
#define STS_PPCE_MASK	(0xff<<16)	/* Per-Port change event 1-16 */
#define STS_ASS		(1<<15)		/* Async Schedule Status */
#define STS_PSS		(1<<14)		/* Periodic Schedule Status */
#define STS_RECL	(1<<13)		/* Reclamation */
#define STS_HALT	(1<<12)		/* Not running (any reason) */
/* some bits reserved */
	/* these STS_* flags are also intr_enable bits (USBINTR) */
#define STS_IAA		(1<<5)		/* Interrupted on async advance */
#define STS_FATAL	(1<<4)		/* such as some PCI access errors */
#define STS_FLR		(1<<3)		/* frame list rolled over */
#define STS_PCD		(1<<2)		/* port change detect */
#define STS_ERR		(1<<1)		/* "error" completion (overflow, ...) */
#define STS_INT		(1<<0)		/* "normal" completion (short, ...) */

	/* USBINTR: offset 0x08 */
	u32		intr_enable;

	/* FRINDEX: offset 0x0C */
	u32		frame_index;	/* current microframe number */
	/* CTRLDSSEGMENT: offset 0x10 */
	u32		segment;	/* address bits 63:32 if needed */
	/* PERIODICLISTBASE: offset 0x14 */
	u32		frame_list;	/* points to periodic list */
	/* ASYNCLISTADDR: offset 0x18 */
	u32		async_next;	/* address of next async queue head */

	u32		reserved1[2];

	/* TXFILLTUNING: offset 0x24 */
	u32		txfill_tuning;	/* TX FIFO Tuning register */
#define TXFIFO_DEFAULT	(8<<16)		/* FIFO burst threshold 8 */

	u32		reserved2[6];

	/* CONFIGFLAG: offset 0x40 */
	u32		configured_flag;
#define FLAG_CF		(1<<0)		/* true: we'll support "high speed" */

	/* PORTSC: offset 0x44 */
	u32		port_status[0];	/* up to N_PORTS */
/* EHCI 1.1 addendum */
#define PORTSC_SUSPEND_STS_ACK 0
#define PORTSC_SUSPEND_STS_NYET 1
#define PORTSC_SUSPEND_STS_STALL 2
#define PORTSC_SUSPEND_STS_ERR 3

#define PORT_DEV_ADDR	(0x7f<<25)		/* device address */
#define PORT_SSTS	(0x3<<23)		/* suspend status */
/* 31:23 reserved */
#define PORT_WKOC_E	(1<<22)		/* wake on overcurrent (enable) */
#define PORT_WKDISC_E	(1<<21)		/* wake on disconnect (enable) */
#define PORT_WKCONN_E	(1<<20)		/* wake on connect (enable) */
/* 19:16 for port testing */
#define PORT_TEST(x)	(((x)&0xf)<<16)	/* Port Test Control */
#define PORT_TEST_PKT	PORT_TEST(0x4)	/* Port Test Control - packet test */
#define PORT_TEST_FORCE	PORT_TEST(0x5)	/* Port Test Control - force enable */
#define PORT_LED_OFF	(0<<14)
#define PORT_LED_AMBER	(1<<14)
#define PORT_LED_GREEN	(2<<14)
#define PORT_LED_MASK	(3<<14)
#define PORT_OWNER	(1<<13)		/* true: companion hc owns this port */
#define PORT_POWER	(1<<12)		/* true: has power (see PPC) */
#define PORT_USB11(x) (((x)&(3<<10)) == (1<<10))	/* USB 1.1 device */
/* 11:10 for detecting lowspeed devices (reset vs release ownership) */
/* 9 reserved */
#define PORT_LPM	(1<<9)		/* LPM transaction */
#define PORT_RESET	(1<<8)		/* reset port */
#define PORT_SUSPEND	(1<<7)		/* suspend port */
#define PORT_RESUME	(1<<6)		/* resume it */
#define PORT_OCC	(1<<5)		/* over current change */
#define PORT_OC		(1<<4)		/* over current active */
#define PORT_PEC	(1<<3)		/* port enable change */
#define PORT_PE		(1<<2)		/* port enable */
#define PORT_CSC	(1<<1)		/* connect status change */
#define PORT_CONNECT	(1<<0)		/* device connected */
#define PORT_RWC_BITS   (PORT_CSC | PORT_PEC | PORT_OCC)

	u32		reserved3[9];

	/* USBMODE: offset 0x68 */
	u32		usbmode;	/* USB Device mode */
#define USBMODE_SDIS	(1<<3)		/* Stream disable */
#define USBMODE_BE	(1<<2)		/* BE/LE endianness select */
#define USBMODE_CM_HC	(3<<0)		/* host controller mode */
#define USBMODE_CM_IDLE	(0<<0)		/* idle state */

	u32		reserved4[6];

/* Moorestown has some non-standard registers, partially due to the fact that
 * its EHCI controller has both TT and LPM support. HOSTPCx are extensions to
 * PORTSCx
 */
	/* HOSTPC: offset 0x84 */
	u32		hostpc[0];	/* HOSTPC extension */
#define HOSTPC_PHCD	(1<<22)		/* Phy clock disable */
#define HOSTPC_PSPD	(3<<25)		/* Port speed detection */

	u32		reserved5[17];

	/* USBMODE_EX: offset 0xc8 */
	u32		usbmode_ex;	/* USB Device mode extension */
#define USBMODE_EX_VBPS	(1<<5)		/* VBus Power Select On */
#define USBMODE_EX_HC	(3<<0)		/* host controller mode */
};
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struct ehci_hcd {			/* one per controller */
	/* timing support */
	enum ehci_hrtimer_event	next_hrtimer_event;
	unsigned		enabled_hrtimer_events;
	ktime_t			hr_timeouts[EHCI_HRTIMER_NUM_EVENTS];
	struct hrtimer		hrtimer;
。。。。。。。
｝
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ehci 使用hrtimer 完成延迟或者周期执行某些动作。根据事件的不同类型决定执行相应的动作。如下代码所示为执行的动作。

/*
 * Handler functions for the hrtimer event types.
 * Keep this array in the same order as the event types indexed by
 * enum ehci_hrtimer_event in ehci.h.
 */
static void (*event_handlers[])(struct ehci_hcd *) = {
	ehci_poll_ASS,			/* EHCI_HRTIMER_POLL_ASS */
	ehci_poll_PSS,			/* EHCI_HRTIMER_POLL_PSS */
	ehci_handle_controller_death,	/* EHCI_HRTIMER_POLL_DEAD */
	ehci_handle_intr_unlinks,	/* EHCI_HRTIMER_UNLINK_INTR */
	end_free_itds,			/* EHCI_HRTIMER_FREE_ITDS */
	end_unlink_async,		/* EHCI_HRTIMER_ACTIVE_UNLINK */
	ehci_handle_start_intr_unlinks,	/* EHCI_HRTIMER_START_UNLINK_INTR */
	unlink_empty_async,		/* EHCI_HRTIMER_ASYNC_UNLINKS 将空的qh从async 链表中摘下*/
	ehci_iaa_watchdog,		/* EHCI_HRTIMER_IAA_WATCHDOG */
	ehci_disable_PSE,		/* EHCI_HRTIMER_DISABLE_PERIODIC */
	ehci_disable_ASE,		/* EHCI_HRTIMER_DISABLE_ASYNC */
	ehci_work,			/* EHCI_HRTIMER_IO_WATCHDOG 将urb归还*/
};

static enum hrtimer_restart ehci_hrtimer_func(struct hrtimer *t)
{
	struct ehci_hcd	*ehci = container_of(t, struct ehci_hcd, hrtimer);
	ktime_t		now;
	unsigned long	events;
	unsigned long	flags;
	unsigned	e;

	spin_lock_irqsave(&ehci->lock, flags);

	events = ehci->enabled_hrtimer_events;
	ehci->enabled_hrtimer_events = 0;
	ehci->next_hrtimer_event = EHCI_HRTIMER_NO_EVENT;

	/*
	 * Check each pending event.  If its time has expired, handle
	 * the event; otherwise re-enable it.
	 */
	now = ktime_get();
	for_each_set_bit(e, &events, EHCI_HRTIMER_NUM_EVENTS) {
		if (now.tv64 >= ehci->hr_timeouts[e].tv64)
			event_handlers[e](ehci);
		else
			ehci_enable_event(ehci, e, false);
	}

	spin_unlock_irqrestore(&ehci->lock, flags);
	return HRTIMER_NORESTART;
}
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下面的部分为不同事件对应不同的延迟时间。在相应的延迟时间之后启动。

static unsigned event_delays_ns[] = {
	1 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_POLL_ASS */
	1 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_POLL_PSS */
	1 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_POLL_DEAD */
	1125 * NSEC_PER_USEC,	/* EHCI_HRTIMER_UNLINK_INTR */
	2 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_FREE_ITDS */
	2 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_ACTIVE_UNLINK */
	5 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_START_UNLINK_INTR */
	6 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_ASYNC_UNLINKS */
	10 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_IAA_WATCHDOG */
	10 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_DISABLE_PERIODIC */
	15 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_DISABLE_ASYNC */
	100 * NSEC_PER_MSEC,	/* EHCI_HRTIMER_IO_WATCHDOG */
};

/* Enable a pending hrtimer event */
static void ehci_enable_event(struct ehci_hcd *ehci, unsigned event,
		bool resched)
{
	ktime_t		*timeout = &ehci->hr_timeouts[event];

	if (resched)
		*timeout = ktime_add(ktime_get(),
				ktime_set(0, event_delays_ns[event]));
	ehci->enabled_hrtimer_events |= (1 << event);

	/* Track only the lowest-numbered pending event */
	if (event < ehci->next_hrtimer_event) {
		ehci->next_hrtimer_event = event;
		hrtimer_start_range_ns(&ehci->hrtimer, *timeout,
				NSEC_PER_MSEC, HRTIMER_MODE_ABS);
	}
}
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ehci_hcd中async处理相关元素：

/* async schedule support */
	struct ehci_qh		*async;
	struct ehci_qh		*dummy;		/* For AMD quirk use */
	struct list_head	async_unlink;
	struct list_head	async_idle;
	unsigned		async_unlink_cycle;
	unsigned		async_count;	/* async activity count */
	__hc32			old_current;	/* Test for QH becoming */
	__hc32			old_token;	/*  inactive during unlink */
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qh所有的状态如下：

#define	QH_STATE_LINKED		1		/* HC sees this */
#define	QH_STATE_UNLINK		2		/* HC may still see this */
#define	QH_STATE_IDLE		3		/* HC doesn't see this */
#define	QH_STATE_UNLINK_WAIT	4		/* LINKED and on unlink q */
#define	QH_STATE_COMPLETING	5		/* don't touch token.HALT */
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submit_async() 函数的调用关系如下图：

turn_on_io_watchdog()启动hrtimer处理echi_work.

/*
 * ehci_work is called from some interrupts, timers, and so on.
 * it calls driver completion functions, after dropping ehci->lock.
 */
static void ehci_work (struct ehci_hcd *ehci)
{
	/* another CPU may drop ehci->lock during a schedule scan while
	 * it reports urb completions.  this flag guards against bogus
	 * attempts at re-entrant schedule scanning.
	 */
	if (ehci->scanning) {
		ehci->need_rescan = true;
		return;
	}
	ehci->scanning = true;

 rescan:
	ehci->need_rescan = false;
	if (ehci->async_count)
		scan_async(ehci);
	if (ehci->intr_count > 0)
		scan_intr(ehci);
	if (ehci->isoc_count > 0)
		scan_isoc(ehci);
	if (ehci->need_rescan)
		goto rescan;
	ehci->scanning = false;

	/* the IO watchdog guards against hardware or driver bugs that
	 * misplace IRQs, and should let us run completely without IRQs.
	 * such lossage has been observed on both VT6202 and VT8235.
	 */
	turn_on_io_watchdog(ehci);
}

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static void scan_async (struct ehci_hcd *ehci)
{
	struct ehci_qh		*qh;
	bool			check_unlinks_later = false;

	ehci->qh_scan_next = ehci->async->qh_next.qh;
	while (ehci->qh_scan_next) {
		qh = ehci->qh_scan_next;
		ehci->qh_scan_next = qh->qh_next.qh;

		/* clean any finished work for this qh */
		if (!list_empty(&qh->qtd_list)) {
			int temp;

			/*
			 * Unlinks could happen here; completion reporting
			 * drops the lock.  That's why ehci->qh_scan_next
			 * always holds the next qh to scan; if the next qh
			 * gets unlinked then ehci->qh_scan_next is adjusted
			 * in single_unlink_async().
			 */
			temp = qh_completions(ehci, qh); //将qh
			if (unlikely(temp)) {
				start_unlink_async(ehci, qh);
			} else if (list_empty(&qh->qtd_list)
					&& qh->qh_state == QH_STATE_LINKED) {
				qh->unlink_cycle = ehci->async_unlink_cycle;
				check_unlinks_later = true;
			}
		}
	}

	/*
	 * Unlink empty entries, reducing DMA usage as well
	 * as HCD schedule-scanning costs.  Delay for any qh
	 * we just scanned, there's a not-unusual case that it
	 * doesn't stay idle for long.
	 */
	if (check_unlinks_later && ehci->rh_state == EHCI_RH_RUNNING &&
			!(ehci->enabled_hrtimer_events &
				BIT(EHCI_HRTIMER_ASYNC_UNLINKS))) {
		ehci_enable_event(ehci, EHCI_HRTIMER_ASYNC_UNLINKS, true);//将空的qh从async链表中拿掉
		++ehci->async_unlink_cycle;
	}
}
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qh_completions() 中将urb返回。

/*
 * Process and free completed qtds for a qh, returning URBs to drivers.
 * Chases up to qh->hw_current.  Returns nonzero if the caller should
 * unlink qh.
 */
static unsigned
qh_completions (struct ehci_hcd *ehci, struct ehci_qh *qh)
{
	struct ehci_qtd		*last, *end = qh->dummy;
	struct list_head	*entry, *tmp;
	int			last_status;
	int			stopped;
	u8			state;
	struct ehci_qh_hw	*hw = qh->hw;

	/* completions (or tasks on other cpus) must never clobber HALT
	 * till we've gone through and cleaned everything up, even when
	 * they add urbs to this qh's queue or mark them for unlinking.
	 *
	 * NOTE:  unlinking expects to be done in queue order.
	 *
	 * It's a bug for qh->qh_state to be anything other than
	 * QH_STATE_IDLE, unless our caller is scan_async() or
	 * scan_intr().
	 */
	state = qh->qh_state;
	qh->qh_state = QH_STATE_COMPLETING;
	stopped = (state == QH_STATE_IDLE);

 rescan:
	last = NULL;
	last_status = -EINPROGRESS;
	qh->dequeue_during_giveback = 0;

	/* remove de-activated QTDs from front of queue.
	 * after faults (including short reads), cleanup this urb
	 * then let the queue advance.
	 * if queue is stopped, handles unlinks.
	 */
	list_for_each_safe (entry, tmp, &qh->qtd_list) {
		struct ehci_qtd	*qtd;
		struct urb	*urb;
		u32		token = 0;

		qtd = list_entry (entry, struct ehci_qtd, qtd_list);
		urb = qtd->urb;

		/* clean up any state from previous QTD ...*/
		if (last) {
			if (likely (last->urb != urb)) {
				ehci_urb_done(ehci, last->urb, last_status);
				last_status = -EINPROGRESS;
			}
			ehci_qtd_free (ehci, last);
			last = NULL;
		}

		/* ignore urbs submitted during completions we reported */
		if (qtd == end)
			break;

		/* hardware copies qtd out of qh overlay */
		rmb ();
		token = hc32_to_cpu(ehci, qtd->hw_token);

		/* always clean up qtds the hc de-activated */
 retry_xacterr:
		if ((token & QTD_STS_ACTIVE) == 0) {

			/* Report Data Buffer Error: non-fatal but useful */
			if (token & QTD_STS_DBE)
				ehci_dbg(ehci,
					"detected DataBufferErr for urb %p ep%d%s len %d, qtd %p [qh %p]\n",
					urb,
					usb_endpoint_num(&urb->ep->desc),
					usb_endpoint_dir_in(&urb->ep->desc) ? "in" : "out",
					urb->transfer_buffer_length,
					qtd,
					qh);

			/* on STALL, error, and short reads this urb must
			 * complete and all its qtds must be recycled.
			 */
			if ((token & QTD_STS_HALT) != 0) {

				/* retry transaction errors until we
				 * reach the software xacterr limit
				 */
				if ((token & QTD_STS_XACT) &&
						QTD_CERR(token) == 0 &&
						++qh->xacterrs < QH_XACTERR_MAX &&
						!urb->unlinked) {
					ehci_dbg(ehci,
	"detected XactErr len %zu/%zu retry %d\n",
	qtd->length - QTD_LENGTH(token), qtd->length, qh->xacterrs);

					/* reset the token in the qtd and the
					 * qh overlay (which still contains
					 * the qtd) so that we pick up from
					 * where we left off
					 */
					token &= ~QTD_STS_HALT;
					token |= QTD_STS_ACTIVE |
							(EHCI_TUNE_CERR << 10);
					qtd->hw_token = cpu_to_hc32(ehci,
							token);
					wmb();
					hw->hw_token = cpu_to_hc32(ehci,
							token);
					goto retry_xacterr;
				}
				stopped = 1;
				qh->unlink_reason |= QH_UNLINK_HALTED;

			/* magic dummy for some short reads; qh won't advance.
			 * that silicon quirk can kick in with this dummy too.
			 *
			 * other short reads won't stop the queue, including
			 * control transfers (status stage handles that) or
			 * most other single-qtd reads ... the queue stops if
			 * URB_SHORT_NOT_OK was set so the driver submitting
			 * the urbs could clean it up.
			 */
			} else if (IS_SHORT_READ (token)
					&& !(qtd->hw_alt_next
						& EHCI_LIST_END(ehci))) {
				stopped = 1;
				qh->unlink_reason |= QH_UNLINK_SHORT_READ;
			}

		/* stop scanning when we reach qtds the hc is using */
		} else if (likely (!stopped
				&& ehci->rh_state >= EHCI_RH_RUNNING)) {
			break;

		/* scan the whole queue for unlinks whenever it stops */
		} else {
			stopped = 1;

			/* cancel everything if we halt, suspend, etc */
			if (ehci->rh_state < EHCI_RH_RUNNING) {
				last_status = -ESHUTDOWN;
				qh->unlink_reason |= QH_UNLINK_SHUTDOWN;
			}

			/* this qtd is active; skip it unless a previous qtd
			 * for its urb faulted, or its urb was canceled.
			 */
			else if (last_status == -EINPROGRESS && !urb->unlinked)
				continue;

			/*
			 * If this was the active qtd when the qh was unlinked
			 * and the overlay's token is active, then the overlay
			 * hasn't been written back to the qtd yet so use its
			 * token instead of the qtd's.  After the qtd is
			 * processed and removed, the overlay won't be valid
			 * any more.
			 */
			if (state == QH_STATE_IDLE &&
					qh->qtd_list.next == &qtd->qtd_list &&
					(hw->hw_token & ACTIVE_BIT(ehci))) {
				token = hc32_to_cpu(ehci, hw->hw_token);
				hw->hw_token &= ~ACTIVE_BIT(ehci);
				qh->should_be_inactive = 1;

				/* An unlink may leave an incomplete
				 * async transaction in the TT buffer.
				 * We have to clear it.
				 */
				ehci_clear_tt_buffer(ehci, qh, urb, token);
			}
		}

		/* unless we already know the urb's status, collect qtd status
		 * and update count of bytes transferred.  in common short read
		 * cases with only one data qtd (including control transfers),
		 * queue processing won't halt.  but with two or more qtds (for
		 * example, with a 32 KB transfer), when the first qtd gets a
		 * short read the second must be removed by hand.
		 */
		if (last_status == -EINPROGRESS) {
			last_status = qtd_copy_status(ehci, urb,
					qtd->length, token);
			if (last_status == -EREMOTEIO
					&& (qtd->hw_alt_next
						& EHCI_LIST_END(ehci)))
				last_status = -EINPROGRESS;

			/* As part of low/full-speed endpoint-halt processing
			 * we must clear the TT buffer (11.17.5).
			 */
			if (unlikely(last_status != -EINPROGRESS &&
					last_status != -EREMOTEIO)) {
				/* The TT's in some hubs malfunction when they
				 * receive this request following a STALL (they
				 * stop sending isochronous packets).  Since a
				 * STALL can't leave the TT buffer in a busy
				 * state (if you believe Figures 11-48 - 11-51
				 * in the USB 2.0 spec), we won't clear the TT
				 * buffer in this case.  Strictly speaking this
				 * is a violation of the spec.
				 */
				if (last_status != -EPIPE)
					ehci_clear_tt_buffer(ehci, qh, urb,
							token);
			}
		}

		/* if we're removing something not at the queue head,
		 * patch the hardware queue pointer.
		 */
		if (stopped && qtd->qtd_list.prev != &qh->qtd_list) {
			last = list_entry (qtd->qtd_list.prev,
					struct ehci_qtd, qtd_list);
			last->hw_next = qtd->hw_next;
		}

		/* remove qtd; it's recycled after possible urb completion */
		list_del (&qtd->qtd_list);
		last = qtd;

		/* reinit the xacterr counter for the next qtd */
		qh->xacterrs = 0;
	}

	/* last urb's completion might still need calling */
	if (likely (last != NULL)) {
		ehci_urb_done(ehci, last->urb, last_status);
		ehci_qtd_free (ehci, last);
	}

	/* Do we need to rescan for URBs dequeued during a giveback? */
	if (unlikely(qh->dequeue_during_giveback)) {
		/* If the QH is already unlinked, do the rescan now. */
		if (state == QH_STATE_IDLE)
			goto rescan;

		/* Otherwise the caller must unlink the QH. */
	}

	/* restore original state; caller must unlink or relink */
	qh->qh_state = state;

	/* be sure the hardware's done with the qh before refreshing
	 * it after fault cleanup, or recovering from silicon wrongly
	 * overlaying the dummy qtd (which reduces DMA chatter).
	 *
	 * We won't refresh a QH that's linked (after the HC
	 * stopped the queue).  That avoids a race:
	 *  - HC reads first part of QH;
	 *  - CPU updates that first part and the token;
	 *  - HC reads rest of that QH, including token
	 * Result:  HC gets an inconsistent image, and then
	 * DMAs to/from the wrong memory (corrupting it).
	 *
	 * That should be rare for interrupt transfers,
	 * except maybe high bandwidth ...
	 */
	if (stopped != 0 || hw->hw_qtd_next == EHCI_LIST_END(ehci))
		qh->unlink_reason |= QH_UNLINK_DUMMY_OVERLAY;

	/* Let the caller know if the QH needs to be unlinked. */
	return qh->unlink_reason;
}

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static void
ehci_urb_done(struct ehci_hcd *ehci, struct urb *urb, int status)
{
	if (usb_pipetype(urb->pipe) == PIPE_INTERRUPT) {
		/* ... update hc-wide periodic stats */
		ehci_to_hcd(ehci)->self.bandwidth_int_reqs--;
	}

	if (unlikely(urb->unlinked)) {
		COUNT(ehci->stats.unlink);
	} else {
		/* report non-error and short read status as zero */
		if (status == -EINPROGRESS || status == -EREMOTEIO)
			status = 0;
		COUNT(ehci->stats.complete);
	}

#ifdef EHCI_URB_TRACE
	ehci_dbg (ehci,
		"%s %s urb %p ep%d%s status %d len %d/%d\n",
		__func__, urb->dev->devpath, urb,
		usb_pipeendpoint (urb->pipe),
		usb_pipein (urb->pipe) ? "in" : "out",
		status,
		urb->actual_length, urb->transfer_buffer_length);
#endif

	usb_hcd_unlink_urb_from_ep(ehci_to_hcd(ehci), urb);
	usb_hcd_giveback_urb(ehci_to_hcd(ehci), urb, status);
}


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32

重要函数

/**
 * usb_add_hcd - finish generic HCD structure initialization and register
 * @hcd: the usb_hcd structure to initialize
 * @irqnum: Interrupt line to allocate
 * @irqflags: Interrupt type flags
 *
 * Finish the remaining parts of generic HCD initialization: allocate the
 * buffers of consistent memory, register the bus, request the IRQ line,
 * and call the driver's reset() and start() routines.
 */
int usb_add_hcd(struct usb_hcd *hcd,
		unsigned int irqnum, unsigned long irqflags)
{
	int retval;
	struct usb_device *rhdev;

	if (IS_ENABLED(CONFIG_USB_PHY) && !hcd->usb_phy) {
		struct usb_phy *phy = usb_get_phy_dev(hcd->self.controller, 0);

		if (IS_ERR(phy)) {
			retval = PTR_ERR(phy);
			if (retval == -EPROBE_DEFER)
				return retval;
		} else {
			retval = usb_phy_init(phy);
			if (retval) {
				usb_put_phy(phy);
				return retval;
			}
			hcd->usb_phy = phy;
			hcd->remove_phy = 1;
		}
	}

	if (IS_ENABLED(CONFIG_GENERIC_PHY) && !hcd->phy) {
		struct phy *phy = phy_get(hcd->self.controller, "usb");

		if (IS_ERR(phy)) {
			retval = PTR_ERR(phy);
			if (retval == -EPROBE_DEFER)
				goto err_phy;
		} else {
			retval = phy_init(phy);
			if (retval) {
				phy_put(phy);
				goto err_phy;
			}
			retval = phy_power_on(phy);
			if (retval) {
				phy_exit(phy);
				phy_put(phy);
				goto err_phy;
			}
			hcd->phy = phy;
			hcd->remove_phy = 1;
		}
	}

	dev_info(hcd->self.controller, "%s\n", hcd->product_desc);

	/* Keep old behaviour if authorized_default is not in [0, 1]. */
	if (authorized_default < 0 || authorized_default > 1) {
		if (hcd->wireless)
			clear_bit(HCD_FLAG_DEV_AUTHORIZED, &hcd->flags);
		else
			set_bit(HCD_FLAG_DEV_AUTHORIZED, &hcd->flags);
	} else {
		if (authorized_default)
			set_bit(HCD_FLAG_DEV_AUTHORIZED, &hcd->flags);
		else
			clear_bit(HCD_FLAG_DEV_AUTHORIZED, &hcd->flags);
	}
	set_bit(HCD_FLAG_HW_ACCESSIBLE, &hcd->flags);

	/* per default all interfaces are authorized */
	set_bit(HCD_FLAG_INTF_AUTHORIZED, &hcd->flags);

	/* HC is in reset state, but accessible.  Now do the one-time init,
	 * bottom up so that hcds can customize the root hubs before hub_wq
	 * starts talking to them.  (Note, bus id is assigned early too.)
	 */
	retval = hcd_buffer_create(hcd);
	if (retval != 0) {
		dev_dbg(hcd->self.controller, "pool alloc failed\n");
		goto err_create_buf;
	}

	retval = usb_register_bus(&hcd->self);
	if (retval < 0)
		goto err_register_bus;

	rhdev = usb_alloc_dev(NULL, &hcd->self, 0);
	if (rhdev == NULL) {
		dev_err(hcd->self.controller, "unable to allocate root hub\n");
		retval = -ENOMEM;
		goto err_allocate_root_hub;
	}
	mutex_lock(&usb_port_peer_mutex);
	hcd->self.root_hub = rhdev;
	mutex_unlock(&usb_port_peer_mutex);

	switch (hcd->speed) {
	case HCD_USB11:
		rhdev->speed = USB_SPEED_FULL;
		break;
	case HCD_USB2:
		rhdev->speed = USB_SPEED_HIGH;
		break;
	case HCD_USB25:
		rhdev->speed = USB_SPEED_WIRELESS;
		break;
	case HCD_USB3:
		rhdev->speed = USB_SPEED_SUPER;
		break;
	case HCD_USB31:
		rhdev->speed = USB_SPEED_SUPER_PLUS;
		break;
	default:
		retval = -EINVAL;
		goto err_set_rh_speed;
	}

	/* wakeup flag init defaults to "everything works" for root hubs,
	 * but drivers can override it in reset() if needed, along with
	 * recording the overall controller's system wakeup capability.
	 */
	device_set_wakeup_capable(&rhdev->dev, 1);

	/* HCD_FLAG_RH_RUNNING doesn't matter until the root hub is
	 * registered.  But since the controller can die at any time,
	 * let's initialize the flag before touching the hardware.
	 */
	set_bit(HCD_FLAG_RH_RUNNING, &hcd->flags);

	/* "reset" is misnamed; its role is now one-time init. the controller
	 * should already have been reset (and boot firmware kicked off etc).
	 */
	if (hcd->driver->reset) {
		retval = hcd->driver->reset(hcd);
		if (retval < 0) {
			dev_err(hcd->self.controller, "can't setup: %d\n",
					retval);
			goto err_hcd_driver_setup;
		}
	}
	hcd->rh_pollable = 1;

	/* NOTE: root hub and controller capabilities may not be the same */
	if (device_can_wakeup(hcd->self.controller)
			&& device_can_wakeup(&hcd->self.root_hub->dev))
		dev_dbg(hcd->self.controller, "supports USB remote wakeup\n");

	/* initialize tasklets */
	init_giveback_urb_bh(&hcd->high_prio_bh);
	init_giveback_urb_bh(&hcd->low_prio_bh);

	/* enable irqs just before we start the controller,
	 * if the BIOS provides legacy PCI irqs.
	 */
	if (usb_hcd_is_primary_hcd(hcd) && irqnum) {
		retval = usb_hcd_request_irqs(hcd, irqnum, irqflags);
		if (retval)
			goto err_request_irq;
	}

	hcd->state = HC_STATE_RUNNING;
	retval = hcd->driver->start(hcd);
	if (retval < 0) {
		dev_err(hcd->self.controller, "startup error %d\n", retval);
		goto err_hcd_driver_start;
	}

	/* starting here, usbcore will pay attention to this root hub */
	retval = register_root_hub(hcd);
	if (retval != 0)
		goto err_register_root_hub;

	retval = sysfs_create_group(&rhdev->dev.kobj, &usb_bus_attr_group);
	if (retval < 0) {
		printk(KERN_ERR "Cannot register USB bus sysfs attributes: %d\n",
		       retval);
		goto error_create_attr_group;
	}
	if (hcd->uses_new_polling && HCD_POLL_RH(hcd))
		usb_hcd_poll_rh_status(hcd);

	return retval;

error_create_attr_group:
	clear_bit(HCD_FLAG_RH_RUNNING, &hcd->flags);
	if (HC_IS_RUNNING(hcd->state))
		hcd->state = HC_STATE_QUIESCING;
	spin_lock_irq(&hcd_root_hub_lock);
	hcd->rh_registered = 0;
	spin_unlock_irq(&hcd_root_hub_lock);

#ifdef CONFIG_PM
	cancel_work_sync(&hcd->wakeup_work);
#endif
	mutex_lock(&usb_bus_idr_lock);
	usb_disconnect(&rhdev);		/* Sets rhdev to NULL */
	mutex_unlock(&usb_bus_idr_lock);
err_register_root_hub:
	hcd->rh_pollable = 0;
	clear_bit(HCD_FLAG_POLL_RH, &hcd->flags);
	del_timer_sync(&hcd->rh_timer);
	hcd->driver->stop(hcd);
	hcd->state = HC_STATE_HALT;
	clear_bit(HCD_FLAG_POLL_RH, &hcd->flags);
	del_timer_sync(&hcd->rh_timer);
err_hcd_driver_start:
	if (usb_hcd_is_primary_hcd(hcd) && hcd->irq > 0)
		free_irq(irqnum, hcd);
err_request_irq:
err_hcd_driver_setup:
err_set_rh_speed:
	usb_put_invalidate_rhdev(hcd);
err_allocate_root_hub:
	usb_deregister_bus(&hcd->self);
err_register_bus:
	hcd_buffer_destroy(hcd);
err_create_buf:
	if (IS_ENABLED(CONFIG_GENERIC_PHY) && hcd->remove_phy && hcd->phy) {
		phy_power_off(hcd->phy);
		phy_exit(hcd->phy);
		phy_put(hcd->phy);
		hcd->phy = NULL;
	}
err_phy:
	if (hcd->remove_phy && hcd->usb_phy) {
		usb_phy_shutdown(hcd->usb_phy);
		usb_put_phy(hcd->usb_phy);
		hcd->usb_phy = NULL;
	}
	return retval;
}
EXPORT_SYMBOL_GPL(usb_add_hcd);

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/**
 * usb_hcd_giveback_urb - return URB from HCD to device driver
 * @hcd: host controller returning the URB
 * @urb: urb being returned to the USB device driver.
 * @status: completion status code for the URB.
 * Context: in_interrupt()
 *
 * This hands the URB from HCD to its USB device driver, using its
 * completion function.  The HCD has freed all per-urb resources
 * (and is done using urb->hcpriv).  It also released all HCD locks;
 * the device driver won't cause problems if it frees, modifies,
 * or resubmits this URB.
 *
 * If @urb was unlinked, the value of @status will be overridden by
 * @urb->unlinked.  Erroneous short transfers are detected in case
 * the HCD hasn't checked for them.
 */
void usb_hcd_giveback_urb(struct usb_hcd *hcd, struct urb *urb, int status)
{
	struct giveback_urb_bh *bh;
	bool running, high_prio_bh;

	/* pass status to tasklet via unlinked */
	if (likely(!urb->unlinked))
		urb->unlinked = status;

	if (!hcd_giveback_urb_in_bh(hcd) && !is_root_hub(urb->dev)) { //没有设置USB_BH(在bottom half 执行giveback, 并且不是根集线器时，不在bottom half执行giveback
		__usb_hcd_giveback_urb(urb);
		return;
	}

	if (usb_pipeisoc(urb->pipe) || usb_pipeint(urb->pipe)) { //如果是同步传输或者中断传输，使用高优先级的tasklet
		bh = &hcd->high_prio_bh;
		high_prio_bh = true;
	} else {
		bh = &hcd->low_prio_bh;
		high_prio_bh = false;
	}

	spin_lock(&bh->lock);
	list_add_tail(&urb->urb_list, &bh->head); //加入到giveback_urb_bh 结构中的链表里边，因为giveback_urb_bh属于usb_hcd结构，所以提交传输的urb在归还时都会加入到这个队列中。
	running = bh->running;
	spin_unlock(&bh->lock);

	if (running)
		;
	else if (high_prio_bh)
		tasklet_hi_schedule(&bh->bh); //触发tasklet
	else
		tasklet_schedule(&bh->bh);
}
EXPORT_SYMBOL_GPL(usb_hcd_giveback_urb);
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tasklet 执行的函数　如下。

static void usb_giveback_urb_bh(unsigned long param)
{
	struct giveback_urb_bh *bh = (struct giveback_urb_bh *)param;
	struct list_head local_list;

	spin_lock_irq(&bh->lock);
	bh->running = true; //tasklet 正在运行
 restart:
	list_replace_init(&bh->head, &local_list); //在锁住的时候把队列拿下来
	spin_unlock_irq(&bh->lock);

	while (!list_empty(&local_list)) {　//归还每一个urb
		struct urb *urb;

		urb = list_entry(local_list.next, struct urb, urb_list);
		list_del_init(&urb->urb_list);
		bh->completing_ep = urb->ep;
		__usb_hcd_giveback_urb(urb);
		bh->completing_ep = NULL;
	}

	/* check if there are new URBs to giveback */
	spin_lock_irq(&bh->lock);
	if (!list_empty(&bh->head))
		goto restart;
	bh->running = false;
	spin_unlock_irq(&bh->lock);
}


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static void __usb_hcd_giveback_urb(struct urb *urb)
{
	struct usb_hcd *hcd = bus_to_hcd(urb->dev->bus);
	struct usb_anchor *anchor = urb->anchor;
	int status = urb->unlinked;
	unsigned long flags;

	urb->hcpriv = NULL;
	if (unlikely((urb->transfer_flags & URB_SHORT_NOT_OK) &&
	    urb->actual_length < urb->transfer_buffer_length &&
	    !status))
		status = -EREMOTEIO;

	unmap_urb_for_dma(hcd, urb);
	usbmon_urb_complete(&hcd->self, urb, status);
	usb_anchor_suspend_wakeups(anchor);
	usb_unanchor_urb(urb);
	if (likely(status == 0))
		usb_led_activity(USB_LED_EVENT_HOST);

	/* pass ownership to the completion handler */
	urb->status = status;

	/*
	 * We disable local IRQs here avoid possible deadlock because
	 * drivers may call spin_lock() to hold lock which might be
	 * acquired in one hard interrupt handler.
	 *
	 * The local_irq_save()/local_irq_restore() around complete()
	 * will be removed if current USB drivers have been cleaned up
	 * and no one may trigger the above deadlock situation when
	 * running complete() in tasklet.
	 */
	local_irq_save(flags);
	urb->complete(urb);   // 释放对urb的占用，回调注册的complete函数
	local_irq_restore(flags);

	usb_anchor_resume_wakeups(anchor);
	atomic_dec(&urb->use_count);
	if (unlikely(atomic_read(&urb->reject)))
		wake_up(&usb_kill_urb_queue);
	usb_put_urb(urb);
}


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/**
 * usb_new_device - perform initial device setup (usbcore-internal)
 * @udev: newly addressed device (in ADDRESS state)
 *
 * This is called with devices which have been detected but not fully
 * enumerated.  The device descriptor is available, but not descriptors
 * for any device configuration.  The caller must have locked either
 * the parent hub (if udev is a normal device) or else the
 * usb_bus_idr_lock (if udev is a root hub).  The parent's pointer to
 * udev has already been installed, but udev is not yet visible through
 * sysfs or other filesystem code.
 *
 * This call is synchronous, and may not be used in an interrupt context.
 *
 * Only the hub driver or root-hub registrar should ever call this.
 *
 * Return: Whether the device is configured properly or not. Zero if the
 * interface was registered with the driver core; else a negative errno
 * value.
 *
 */
int usb_new_device(struct usb_device *udev)
{
	int err;

	if (udev->parent) {
		/* Initialize non-root-hub device wakeup to disabled;
		 * device (un)configuration controls wakeup capable
		 * sysfs power/wakeup controls wakeup enabled/disabled
		 */
		device_init_wakeup(&udev->dev, 0);
	}

	/* Tell the runtime-PM framework the device is active */
	pm_runtime_set_active(&udev->dev);
	pm_runtime_get_noresume(&udev->dev);
	pm_runtime_use_autosuspend(&udev->dev);
	pm_runtime_enable(&udev->dev);

	/* By default, forbid autosuspend for all devices.  It will be
	 * allowed for hubs during binding.
	 */
	usb_disable_autosuspend(udev);

	err = usb_enumerate_device(udev);	/* Read descriptors */
	if (err < 0)
		goto fail;
	dev_dbg(&udev->dev, "udev %d, busnum %d, minor = %d\n",
			udev->devnum, udev->bus->busnum,
			(((udev->bus->busnum-1) * 128) + (udev->devnum-1)));
	/* export the usbdev device-node for libusb */
	udev->dev.devt = MKDEV(USB_DEVICE_MAJOR,
			(((udev->bus->busnum-1) * 128) + (udev->devnum-1)));

	/* Tell the world! */
	announce_device(udev);

	if (udev->serial)
		add_device_randomness(udev->serial, strlen(udev->serial));
	if (udev->product)
		add_device_randomness(udev->product, strlen(udev->product));
	if (udev->manufacturer)
		add_device_randomness(udev->manufacturer,
				      strlen(udev->manufacturer));

	device_enable_async_suspend(&udev->dev);

	/* check whether the hub or firmware marks this port as non-removable */
	if (udev->parent)
		set_usb_port_removable(udev);

	/* Register the device.  The device driver is responsible
	 * for configuring the device and invoking the add-device
	 * notifier chain (used by usbfs and possibly others).
	 */
	err = device_add(&udev->dev);
	if (err) {
		dev_err(&udev->dev, "can't device_add, error %d\n", err);
		goto fail;
	}

	/* Create link files between child device and usb port device. */
	if (udev->parent) {
		struct usb_hub *hub = usb_hub_to_struct_hub(udev->parent);
		int port1 = udev->portnum;
		struct usb_port	*port_dev = hub->ports[port1 - 1];

		err = sysfs_create_link(&udev->dev.kobj,
				&port_dev->dev.kobj, "port");
		if (err)
			goto fail;

		err = sysfs_create_link(&port_dev->dev.kobj,
				&udev->dev.kobj, "device");
		if (err) {
			sysfs_remove_link(&udev->dev.kobj, "port");
			goto fail;
		}

		if (!test_and_set_bit(port1, hub->child_usage_bits))
			pm_runtime_get_sync(&port_dev->dev);
	}

	(void) usb_create_ep_devs(&udev->dev, &udev->ep0, udev);
	usb_mark_last_busy(udev);
	pm_runtime_put_sync_autosuspend(&udev->dev);
	return err;

fail:
	usb_set_device_state(udev, USB_STATE_NOTATTACHED);
	pm_runtime_disable(&udev->dev);
	pm_runtime_set_suspended(&udev->dev);
	return err;
}


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usb_device

struct usb_device {
	int		devnum;
	char		devpath[16];
	u32		route;
	enum usb_device_state	state;
	enum usb_device_speed	speed;

	struct usb_tt	*tt;
	int		ttport;

	unsigned int toggle[2];

	struct usb_device *parent;
	struct usb_bus *bus;
	struct usb_host_endpoint ep0;

	struct device dev;

	struct usb_device_descriptor descriptor; //设备描述符，内部有配置描述符的数量。
	struct usb_host_bos *bos;
	struct usb_host_config *config; //配置描述符数组，host_config中有接口描述符

	struct usb_host_config *actconfig;
	struct usb_host_endpoint *ep_in[16];
	struct usb_host_endpoint *ep_out[16];

	char **rawdescriptors;

	unsigned short bus_mA;
	u8 portnum;
	u8 level;

	unsigned can_submit:1;
	unsigned persist_enabled:1;
	unsigned have_langid:1;
	unsigned authorized:1;
	unsigned authenticated:1;
	unsigned wusb:1;
	unsigned lpm_capable:1;
	unsigned usb2_hw_lpm_capable:1;
	unsigned usb2_hw_lpm_besl_capable:1;
	unsigned usb2_hw_lpm_enabled:1;
	unsigned usb2_hw_lpm_allowed:1;
	unsigned usb3_lpm_u1_enabled:1;
	unsigned usb3_lpm_u2_enabled:1;
	int string_langid;

	/* static strings from the device */
	char *product;
	char *manufacturer;
	char *serial;

	struct list_head filelist;

	int maxchild;

	u32 quirks;
	atomic_t urbnum;

	unsigned long active_duration;

#ifdef CONFIG_PM
	unsigned long connect_time;

	unsigned do_remote_wakeup:1;
	unsigned reset_resume:1;
	unsigned port_is_suspended:1;
#endif
	struct wusb_dev *wusb_dev;
	int slot_id;
	enum usb_device_removable removable;
	struct usb2_lpm_parameters l1_params;
	struct usb3_lpm_parameters u1_params;
	struct usb3_lpm_parameters u2_params;
	unsigned lpm_disable_count;
};
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