[PATCH] USB: ehci-hcd updates

This should apply to 2.5.59 too.  It seems to get rid of some pesky
hangs, on at least some hardware, but I won't have time to test it
on either VIA version ... maybe someone else will make the time?  :)

      New QH state prevents a re-activation race
	- nobody can un-halt a qh before its cleanup is done
	- resubmit-from-completion had this race (some usbtest cases)
	  as could some normal submit paths on busy endpoints (storage)
	- faster controllers would trip on this more consistently

      Queues of qtds
	- work harder to avoid ever modifing any qh in software
	- short reads block queue advance much less often
	- be more cautious with large (>~19KB) unaligned buffers

      Unlinking urbs
	- if qtd unlinked is at queue head, use its latest status
	  (main effect is reporting bytes from partial transfers)
	- another new qh state:  defer qh unlink if IAA is busy
	  (eliminates a busy-wait loop in a rare scenario)

      Enable features to improve bus utilization
	- PCI MWI ... can produce better write throughput; and by
	  using right cacheline size, sometimes read throughput too
	- USB NAK throttle ... sometimes reduces PCI access rates

      Other
	- async dump shows more funky qh+qtd states, and NAK count
	- cope with with some of the sprintf wierdness
	- periodic dump is usually smaller (so is that schedule)
      	- minor cleanups

drivers/usb/host/ehci-dbg.c

@@ -277,7 +277,26 @@ static inline void remove_debug_files (struct ehci_hcd *bus) { }
 		default: tmp = '?'; break; \
 		}; tmp; })
 
-static void qh_lines (struct ehci_qh *qh, char **nextp, unsigned *sizep)
+static inline char token_mark (u32 token)
+{
+	token = le32_to_cpu (token);
+	if (token & QTD_STS_ACTIVE)
+		return '*';
+	if (token & QTD_STS_HALT)
+		return '-';
+	if (QTD_PID (token) != 1 /* not IN: OUT or SETUP */
+			|| QTD_LENGTH (token) == 0)
+		return ' ';
+	/* tries to advance through hw_alt_next */
+	return '/';
+}
+
+static void qh_lines (
+	struct ehci_hcd *ehci,
+	struct ehci_qh *qh,
+	char **nextp,
+	unsigned *sizep
+)
 {
 	u32			scratch;
 	u32			hw_curr;
@@ -286,26 +305,49 @@ static void qh_lines (struct ehci_qh *qh, char **nextp, unsigned *sizep)
 	unsigned		temp;
 	unsigned		size = *sizep;
 	char			*next = *nextp;
-
+	char			mark;
+
+	mark = token_mark (qh->hw_token);
+	if (mark == '/') {	/* qh_alt_next controls qh advance? */
+		if ((qh->hw_alt_next & QTD_MASK) == ehci->async->hw_alt_next)
+			mark = '#';	/* blocked */
+		else if (qh->hw_alt_next & cpu_to_le32 (0x01))
+			mark = '.';	/* use hw_qtd_next */
+		/* else alt_next points to some other qtd */
+	}
 	scratch = cpu_to_le32p (&qh->hw_info1);
-	hw_curr = cpu_to_le32p (&qh->hw_current);
+	hw_curr = (mark == '*') ? cpu_to_le32p (&qh->hw_current) : 0;
 	temp = snprintf (next, size,
-			"qh/%p dev%d %cs ep%d %08x %08x (%08x %08x)",
+			"qh/%p dev%d %cs ep%d %08x %08x (%08x%c %s nak%d)",
 			qh, scratch & 0x007f,
 			speed_char (scratch),
 			(scratch >> 8) & 0x000f,
 			scratch, cpu_to_le32p (&qh->hw_info2),
-			hw_curr, cpu_to_le32p (&qh->hw_token));
+			cpu_to_le32p (&qh->hw_token), mark,
+			(cpu_to_le32 (0x8000000) & qh->hw_token)
+				? "data0" : "data1",
+			(cpu_to_le32p (&qh->hw_alt_next) >> 1) & 0x0f);
 	size -= temp;
 	next += temp;
 
+	/* hc may be modifying the list as we read it ... */
 	list_for_each (entry, &qh->qtd_list) {
 		td = list_entry (entry, struct ehci_qtd, qtd_list);
 		scratch = cpu_to_le32p (&td->hw_token);
+		mark = ' ';
+		if (hw_curr == td->qtd_dma)
+			mark = '*';
+		else if (qh->hw_qtd_next == td->qtd_dma)
+			mark = '+';
+		else if (QTD_LENGTH (scratch)) {
+			if (td->hw_alt_next == ehci->async->hw_alt_next)
+				mark = '#';
+			else if (td->hw_alt_next != EHCI_LIST_END)
+				mark = '/';
+		}
 		temp = snprintf (next, size,
-				"\n\t%std/%p %s len=%d %08x urb %p",
-				(hw_curr == td->qtd_dma) ? "*" : "",
-				td, ({ char *tmp;
+				"\n\t%p%c%s len=%d %08x urb %p",
+				td, mark, ({ char *tmp;
 				 switch ((scratch>>8)&0x03) {
 				 case 0: tmp = "out"; break;
 				 case 1: tmp = "in"; break;
@@ -315,13 +357,27 @@ static void qh_lines (struct ehci_qh *qh, char **nextp, unsigned *sizep)
 				(scratch >> 16) & 0x7fff,
 				scratch,
 				td->urb);
+		if (temp < 0)
+			temp = 0;
+		else if (size < temp)
+			temp = size;
 		size -= temp;
 		next += temp;
+		if (temp == size)
+			goto done;
 	}
 
 	temp = snprintf (next, size, "\n");
-	*sizep = size - temp;
-	*nextp = next + temp;
+	if (temp < 0)
+		temp = 0;
+	else if (size < temp)
+		temp = size;
+	size -= temp;
+	next += temp;
+
+done:
+	*sizep = size;
+	*nextp = next;
 }
 
 static ssize_t
@@ -344,14 +400,15 @@ show_async (struct device *dev, char *buf)
 	 * one QH per line, and TDs we know about
 	 */
 	spin_lock_irqsave (&ehci->lock, flags);
-	for (qh = ehci->async->qh_next.qh; qh; qh = qh->qh_next.qh)
-		qh_lines (qh, &next, &size);
-	if (ehci->reclaim) {
+	for (qh = ehci->async->qh_next.qh; size > 0 && qh; qh = qh->qh_next.qh)
+		qh_lines (ehci, qh, &next, &size);
+	if (ehci->reclaim && size > 0) {
 		temp = snprintf (next, size, "\nreclaim =\n");
 		size -= temp;
 		next += temp;
 
-		qh_lines (ehci->reclaim, &next, &size);
+		for (qh = ehci->reclaim; size > 0 && qh; qh = qh->reclaim)
+			qh_lines (ehci, qh, &next, &size);
 	}
 	spin_unlock_irqrestore (&ehci->lock, flags);
 
@@ -421,7 +478,7 @@ show_periodic (struct device *dev, char *buf)
 						scratch & 0x007f,
 						(scratch >> 8) & 0x000f,
 						p.qh->usecs, p.qh->c_usecs,
-						scratch >> 16);
+						0x7ff & (scratch >> 16));
 
 					/* FIXME TD info too */
 
@@ -490,7 +547,8 @@ show_registers (struct device *dev, char *buf)
 
 	/* Capability Registers */
 	i = readw (&ehci->caps->hci_version);
-	temp = snprintf (next, size, "EHCI %x.%02x, hcd state %d\n",
+	temp = snprintf (next, size,
+		"EHCI %x.%02x, hcd state %d (version " DRIVER_VERSION ")\n",
 		i >> 8, i & 0x0ff, ehci->hcd.state);
 	size -= temp;
 	next += temp;

drivers/usb/host/ehci-hcd.c

@@ -94,7 +94,7 @@
  * 2001-June	Works with usb-storage and NEC EHCI on 2.4
  */
 
-#define DRIVER_VERSION "2002-Nov-29"
+#define DRIVER_VERSION "2003-Jan-22"
 #define DRIVER_AUTHOR "David Brownell"
 #define DRIVER_DESC "USB 2.0 'Enhanced' Host Controller (EHCI) Driver"
 
@@ -110,10 +110,11 @@ static const char	hcd_name [] = "ehci-hcd";
 
 /* magic numbers that can affect system performance */
 #define	EHCI_TUNE_CERR		3	/* 0-3 qtd retries; 0 == don't stop */
-#define	EHCI_TUNE_RL_HS		0	/* nak throttle; see 4.9 */
+#define	EHCI_TUNE_RL_HS		4	/* nak throttle; see 4.9 */
 #define	EHCI_TUNE_RL_TT		0
 #define	EHCI_TUNE_MULT_HS	1	/* 1-3 transactions/uframe; 4.10.3 */
 #define	EHCI_TUNE_MULT_TT	1
+#define	EHCI_TUNE_FLS		2	/* (small) 256 frame schedule */
 
 #define EHCI_WATCHDOG_JIFFIES	(HZ/100)	/* arbitrary; ~10 msec */
 #define EHCI_ASYNC_JIFFIES	(HZ/20)		/* async idle timeout */
@@ -416,13 +417,26 @@ static int ehci_start (struct usb_hcd *hcd)
 			ehci_info (ehci, "enabled 64bit PCI DMA\n");
 	}
 
+	/* help hc dma work well with cachelines */
+	pci_set_mwi (ehci->hcd.pdev);
+
 	/* clear interrupt enables, set irq latency */
 	temp = readl (&ehci->regs->command) & 0xff;
 	if (log2_irq_thresh < 0 || log2_irq_thresh > 6)
 		log2_irq_thresh = 0;
 	temp |= 1 << (16 + log2_irq_thresh);
 	// if hc can park (ehci >= 0.96), default is 3 packets per async QH 
-	// keeping default periodic framelist size
+	if (HCC_PGM_FRAMELISTLEN (hcc_params)) {
+		/* periodic schedule size can be smaller than default */
+		temp &= ~(3 << 2);
+		temp |= (EHCI_TUNE_FLS << 2);
+		switch (EHCI_TUNE_FLS) {
+		case 0: ehci->periodic_size = 1024; break;
+		case 1: ehci->periodic_size = 512; break;
+		case 2: ehci->periodic_size = 256; break;
+		default:	BUG ();
+		}
+	}
 	temp &= ~(CMD_IAAD | CMD_ASE | CMD_PSE),
 	// Philips, Intel, and maybe others need CMD_RUN before the
 	// root hub will detect new devices (why?); NEC doesn't
@@ -759,7 +773,6 @@ static int ehci_urb_dequeue (struct usb_hcd *hcd, struct urb *urb)
 	struct ehci_hcd		*ehci = hcd_to_ehci (hcd);
 	struct ehci_qh		*qh;
 	unsigned long		flags;
-	int			maybe_irq = 1;
 
 	spin_lock_irqsave (&ehci->lock, flags);
 	switch (usb_pipetype (urb->pipe)) {
@@ -769,23 +782,23 @@ static int ehci_urb_dequeue (struct usb_hcd *hcd, struct urb *urb)
 		qh = (struct ehci_qh *) urb->hcpriv;
 		if (!qh)
 			break;
-		while (qh->qh_state == QH_STATE_LINKED
+
+		/* if we need to use IAA and it's busy, defer */
+		if (qh->qh_state == QH_STATE_LINKED
 				&& ehci->reclaim
 				&& HCD_IS_RUNNING (ehci->hcd.state)
 				) {
-			spin_unlock_irqrestore (&ehci->lock, flags);
+			struct ehci_qh		*last;
 
-			if (maybe_irq) {
-				if (in_interrupt ())
-					return -EAGAIN;
-				maybe_irq = 0;
-			}
-			/* let pending unlinks complete, so this can start */
-			wait_ms (1);
+			for (last = ehci->reclaim;
+					last->reclaim;
+					last = last->reclaim)
+				continue;
+			qh->qh_state = QH_STATE_UNLINK_WAIT;
+			last->reclaim = qh;
 
-			spin_lock_irqsave (&ehci->lock, flags);
-		}
-		if (!HCD_IS_RUNNING (ehci->hcd.state) && ehci->reclaim)
+		/* bypass IAA if the hc can't care */
+		} else if (!HCD_IS_RUNNING (ehci->hcd.state) && ehci->reclaim)
 			end_unlink_async (ehci, NULL);
 
 		/* something else might have unlinked the qh by now */

drivers/usb/host/ehci-mem.c

@@ -75,8 +75,6 @@ static struct ehci_qtd *ehci_qtd_alloc (struct ehci_hcd *ehci, int flags)
 	qtd = pci_pool_alloc (ehci->qtd_pool, flags, &dma);
 	if (qtd != 0) {
 		ehci_qtd_init (qtd, dma);
-		if (ehci->async)
-			qtd->hw_alt_next = ehci->async->hw_alt_next;
 	}
 	return qtd;
 }

drivers/usb/host/ehci-q.c

@@ -43,7 +43,8 @@
 /* fill a qtd, returning how much of the buffer we were able to queue up */
 
 static int
-qtd_fill (struct ehci_qtd *qtd, dma_addr_t buf, size_t len, int token)
+qtd_fill (struct ehci_qtd *qtd, dma_addr_t buf, size_t len,
+		int token, int maxpacket)
 {
 	int	i, count;
 	u64	addr = buf;
@@ -69,6 +70,10 @@ qtd_fill (struct ehci_qtd *qtd, dma_addr_t buf, size_t len, int token)
 			else
 				count = len;
 		}
+
+		/* short packets may only terminate transfers */
+		if (count != len)
+			count -= (count % maxpacket);
 	}
 	qtd->hw_token = cpu_to_le32 ((count << 16) | token);
 	qtd->length = count;
@@ -85,7 +90,7 @@ qh_update (struct ehci_hcd *ehci, struct ehci_qh *qh, struct ehci_qtd *qtd)
 {
 	qh->hw_current = 0;
 	qh->hw_qtd_next = QTD_NEXT (qtd->qtd_dma);
-	qh->hw_alt_next = ehci->async->hw_alt_next;
+	qh->hw_alt_next = EHCI_LIST_END;
 
 	/* HC must see latest qtd and qh data before we clear ACTIVE+HALT */
 	wmb ();
@@ -96,7 +101,7 @@ qh_update (struct ehci_hcd *ehci, struct ehci_qh *qh, struct ehci_qtd *qtd)
 
 #define IS_SHORT_READ(token) (QTD_LENGTH (token) != 0 && QTD_PID (token) == 1)
 
-static inline void qtd_copy_status (
+static void qtd_copy_status (
 	struct ehci_hcd *ehci,
 	struct urb *urb,
 	size_t length,
@@ -224,12 +229,24 @@ qh_completions (struct ehci_hcd *ehci, struct ehci_qh *qh, struct pt_regs *regs)
 {
 	struct ehci_qtd		*last = 0, *end = qh->dummy;
 	struct list_head	*entry, *tmp;
-	int			stopped = 0;
+	int			stopped;
 	unsigned		count = 0;
+	int			do_status = 0;
+	u8			state;
 
 	if (unlikely (list_empty (&qh->qtd_list)))
 		return count;
 
+	/* 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.
+	 */
+	state = qh->qh_state;
+	qh->qh_state = QH_STATE_COMPLETING;
+	stopped = (state == QH_STATE_IDLE);
+
 	/* remove de-activated QTDs from front of queue.
 	 * after faults (including short reads), cleanup this urb
 	 * then let the queue advance.
@@ -261,7 +278,6 @@ qh_completions (struct ehci_hcd *ehci, struct ehci_qh *qh, struct pt_regs *regs)
 		rmb ();
 		token = le32_to_cpu (qtd->hw_token);
 		stopped = stopped
-			|| (qh->qh_state == QH_STATE_IDLE)
 			|| (HALT_BIT & qh->hw_token) != 0
 			|| (ehci->hcd.state == USB_STATE_HALT);
 
@@ -271,36 +287,53 @@ qh_completions (struct ehci_hcd *ehci, struct ehci_qh *qh, struct pt_regs *regs)
 			/* magic dummy for short reads; won't advance */
 			if (IS_SHORT_READ (token)
 					&& !(token & QTD_STS_HALT)
-					&& ehci->async->hw_alt_next
-						== qh->hw_alt_next)
+					&& (qh->hw_alt_next & QTD_MASK)
+						== ehci->async->hw_alt_next) {
+				stopped = 1;
 				goto halt;
+			}
 
 		/* stop scanning when we reach qtds the hc is using */
 		} else if (likely (!stopped)) {
-			last = 0;
 			break;
 
 		} else {
-			/* ignore active qtds unless some previous qtd
+			/* ignore active urbs unless some previous qtd
 			 * for the urb faulted (including short read) or
 			 * its urb was canceled.  we may patch qh or qtds.
 			 */
-			if ((token & QTD_STS_ACTIVE)
-					&& urb->status == -EINPROGRESS) {
-				last = 0;
+			if (likely (urb->status == -EINPROGRESS))
+				continue;
+			
+			/* issue status after short control reads */
+			if (unlikely (do_status != 0)
+					&& QTD_PID (token) == 0 /* OUT */) {
+				do_status = 0;
 				continue;
 			}
+
+			/* token in overlay may be most current */
+			if (state == QH_STATE_IDLE
+					&& cpu_to_le32 (qtd->qtd_dma)
+						== qh->hw_current)
+				token = le32_to_cpu (qh->hw_token);
+
+			/* force halt for unlinked or blocked qh, so we'll
+			 * patch the qh later and so that completions can't
+			 * activate it while we "know" it's stopped.
+			 */
 			if ((HALT_BIT & qh->hw_token) == 0) {
 halt:
 				qh->hw_token |= HALT_BIT;
 				wmb ();
-				stopped = 1;
 			}
 		}
  
 		/* remove it from the queue */
 		spin_lock (&urb->lock);
 		qtd_copy_status (ehci, urb, qtd->length, token);
+		do_status = (urb->status == -EREMOTEIO)
+				&& usb_pipecontrol (urb->pipe);
 		spin_unlock (&urb->lock);
 
 		if (stopped && qtd->qtd_list.prev != &qh->qtd_list) {
@@ -319,6 +352,9 @@ qh_completions (struct ehci_hcd *ehci, struct ehci_qh *qh, struct pt_regs *regs)
 		ehci_qtd_free (ehci, last);
 	}
 
+	/* restore original state; caller must unlink or relink */
+	qh->qh_state = state;
+
 	/* update qh after fault cleanup */
 	if (unlikely ((HALT_BIT & qh->hw_token) != 0)) {
 		qh_update (ehci, qh,
@@ -367,7 +403,7 @@ qh_urb_transaction (
 	struct ehci_qtd		*qtd, *qtd_prev;
 	dma_addr_t		buf;
 	int			len, maxpacket;
-	int			is_input, status_patch = 0;
+	int			is_input;
 	u32			token;
 
 	/*
@@ -388,7 +424,7 @@ qh_urb_transaction (
 	if (usb_pipecontrol (urb->pipe)) {
 		/* SETUP pid */
 		qtd_fill (qtd, urb->setup_dma, sizeof (struct usb_ctrlrequest),
-			token | (2 /* "setup" */ << 8));
+			token | (2 /* "setup" */ << 8), 8);
 
 		/* ... and always at least one more pid */
 		token ^= QTD_TOGGLE;
@@ -399,10 +435,6 @@ qh_urb_transaction (
 		qtd->urb = urb;
 		qtd_prev->hw_next = QTD_NEXT (qtd->qtd_dma);
 		list_add_tail (&qtd->qtd_list, head);
-
-		if (len > 0 && is_input
-				&& !(urb->transfer_flags & URB_SHORT_NOT_OK))
-			status_patch = 1;
 	} 
 
 	/*
@@ -413,6 +445,7 @@ qh_urb_transaction (
 	else
 		buf = 0;
 
+	// FIXME this 'buf' check break some zlps...
 	if (!buf || is_input)
 		token |= (1 /* "in" */ << 8);
 	/* else it's already initted to "out" pid (0 << 8) */
@@ -427,9 +460,11 @@ qh_urb_transaction (
 	for (;;) {
 		int this_qtd_len;
 
-		this_qtd_len = qtd_fill (qtd, buf, len, token);
+		this_qtd_len = qtd_fill (qtd, buf, len, token, maxpacket);
 		len -= this_qtd_len;
 		buf += this_qtd_len;
+		if (is_input)
+			qtd->hw_alt_next = ehci->async->hw_alt_next;
 
 		/* qh makes control packets use qtd toggle; maybe switch it */
 		if ((maxpacket & (this_qtd_len + (maxpacket - 1))) == 0)
@@ -447,6 +482,13 @@ qh_urb_transaction (
 		list_add_tail (&qtd->qtd_list, head);
 	}
 
+	/* unless the bulk/interrupt caller wants a chance to clean
+	 * up after short reads, hc should advance qh past this urb
+	 */
+	if (likely ((urb->transfer_flags & URB_SHORT_NOT_OK) == 0
+				|| usb_pipecontrol (urb->pipe)))
+		qtd->hw_alt_next = EHCI_LIST_END;
+
 	/*
 	 * control requests may need a terminating data "status" ack;
 	 * bulk ones may need a terminating short packet (zero length).
@@ -473,21 +515,8 @@ qh_urb_transaction (
 			list_add_tail (&qtd->qtd_list, head);
 
 			/* never any data in such packets */
-			qtd_fill (qtd, 0, 0, token);
-		}
+			qtd_fill (qtd, 0, 0, token, 0);
 		}
-
-	/* if we're permitting a short control read, we want the hardware to
-	 * just continue after short data and send the status ack.  it can do
-	 * that on the last data packet (typically the only one).  for other
-	 * packets, software fixup is needed (in qh_completions).
-	 */
-	if (status_patch) {
-		struct ehci_qtd		*prev;
-
-		prev = list_entry (qtd->qtd_list.prev,
-				struct ehci_qtd, qtd_list);
-		prev->hw_alt_next = QTD_NEXT (qtd->qtd_dma);
 	}
 
 	/* by default, enable interrupt on urb completion */
@@ -611,6 +640,7 @@ qh_make (
 
 	case USB_SPEED_FULL:
 		/* EPS 0 means "full" */
+		if (type != PIPE_INTERRUPT)
 			info1 |= (EHCI_TUNE_RL_TT << 28);
 		if (type == PIPE_CONTROL) {
 			info1 |= (1 << 27);	/* for TT */
@@ -628,12 +658,13 @@ qh_make (
 
 	case USB_SPEED_HIGH:		/* no TT involved */
 		info1 |= (2 << 12);	/* EPS "high" */
-		info1 |= (EHCI_TUNE_RL_HS << 28);
 		if (type == PIPE_CONTROL) {
+			info1 |= (EHCI_TUNE_RL_HS << 28);
 			info1 |= 64 << 16;	/* usb2 fixed maxpacket */
 			info1 |= 1 << 14;	/* toggle from qtd */
 			info2 |= (EHCI_TUNE_MULT_HS << 30);
 		} else if (type == PIPE_BULK) {
+			info1 |= (EHCI_TUNE_RL_HS << 28);
 			info1 |= 512 << 16;	/* usb2 fixed maxpacket */
 			info2 |= (EHCI_TUNE_MULT_HS << 30);
 		} else {		/* PIPE_INTERRUPT */
@@ -769,8 +800,7 @@ static struct ehci_qh *qh_append_tds (
 				&& !usb_pipecontrol (urb->pipe)) {
 			/* "never happens": drivers do stall cleanup right */
 			if (qh->qh_state != QH_STATE_IDLE
-					&& (cpu_to_le32 (QTD_STS_HALT)
-						& qh->hw_token) == 0)
+					&& qh->qh_state != QH_STATE_COMPLETING)
 				ehci_warn (ehci, "clear toggle dev%d "
 						"ep%d%s: not idle\n",
 						usb_pipedevice (urb->pipe),
@@ -809,7 +839,6 @@ static struct ehci_qh *qh_append_tds (
 			__list_splice (qtd_list, qh->qtd_list.prev);
 
 			ehci_qtd_init (qtd, qtd->qtd_dma);
-			qtd->hw_alt_next = ehci->async->hw_alt_next;
 			qh->dummy = qtd;
 
 			/* hc must see the new dummy at list end */
@@ -877,9 +906,12 @@ submit_async (
 
 /* the async qh for the qtds being reclaimed are now unlinked from the HC */
 
+static void start_unlink_async (struct ehci_hcd *ehci, struct ehci_qh *qh);
+
 static void end_unlink_async (struct ehci_hcd *ehci, struct pt_regs *regs)
 {
 	struct ehci_qh		*qh = ehci->reclaim;
+	struct ehci_qh		*next;
 
 	del_timer (&ehci->watchdog);
 
@@ -890,6 +922,10 @@ static void end_unlink_async (struct ehci_hcd *ehci, struct pt_regs *regs)
 	ehci->reclaim = 0;
 	ehci->reclaim_ready = 0;
 
+	/* other unlink(s) may be pending (in QH_STATE_UNLINK_WAIT) */
+	next = qh->reclaim;
+	qh->reclaim = 0;
+
 	qh_completions (ehci, qh, regs);
 
 	if (!list_empty (&qh->qtd_list)
@@ -909,6 +945,9 @@ static void end_unlink_async (struct ehci_hcd *ehci, struct pt_regs *regs)
 					jiffies + EHCI_ASYNC_JIFFIES);
 		}
 	}
+
+	if (next)
+		start_unlink_async (ehci, next);
 }
 
 /* makes sure the async qh will become idle */
@@ -921,7 +960,8 @@ static void start_unlink_async (struct ehci_hcd *ehci, struct ehci_qh *qh)
 
 #ifdef DEBUG
 	if (ehci->reclaim
-			|| qh->qh_state != QH_STATE_LINKED
+			|| (qh->qh_state != QH_STATE_LINKED
+				&& qh->qh_state != QH_STATE_UNLINK_WAIT)
 #ifdef CONFIG_SMP
 // this macro lies except on SMP compiles
 			|| !spin_is_locked (&ehci->lock)
@@ -953,6 +993,9 @@ static void start_unlink_async (struct ehci_hcd *ehci, struct ehci_qh *qh)
 	wmb ();
 
 	if (unlikely (ehci->hcd.state == USB_STATE_HALT)) {
+		/* if (unlikely (qh->reclaim != 0))
+		 * 	this will recurse, probably not much
+		 */
 		end_unlink_async (ehci, NULL);
 		return;
 	}

drivers/usb/host/ehci.h

@@ -236,12 +236,12 @@ struct ehci_qtd {
 	/* the rest is HCD-private */
 	dma_addr_t		qtd_dma;		/* qtd address */
 	struct list_head	qtd_list;		/* sw qtd list */
-
-	/* dma same in urb's qtds, except 1st control qtd (setup buffer) */
 	struct urb		*urb;			/* qtd's urb */
 	size_t			length;			/* length of buffer */
 } __attribute__ ((aligned (32)));
 
+#define QTD_MASK cpu_to_le32 (~0x1f)	/* mask NakCnt+T in qh->hw_alt_next */
+
 /*-------------------------------------------------------------------------*/
 
 /* type tag from {qh,itd,sitd,fstn}->hw_next */
@@ -305,6 +305,7 @@ struct ehci_qh {
 	union ehci_shadow	qh_next;	/* ptr to qh; or periodic */
 	struct list_head	qtd_list;	/* sw qtd list */
 	struct ehci_qtd		*dummy;
+	struct ehci_qh		*reclaim;	/* next to reclaim */
 
 	atomic_t		refcount;
 	unsigned		stamp;
@@ -313,6 +314,8 @@ struct ehci_qh {
 #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 reclaim q */
+#define	QH_STATE_COMPLETING	5		/* don't touch token.HALT */
 
 	/* periodic schedule info */
 	u8			usecs;		/* intr bandwidth */