USB: EHCI: simplify isochronous scanning

This patch (as1587) simplifies ehci-hcd's scan_isoc() routine by
eliminating some local variables, declaring boolean-valued values as
bool rather than unsigned, changing variable names to make more sense,
and so on.

The logic at the end of the routine is cut down significantly.  The
scanning doesn't have to catch up all the way to where the hardware
is; it merely has to catch up to where the hardware was when the last
interrupt occurred.  If the hardware has made more progress since then
and issued another interrupt, a rescan will catch up to it.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/ehci-hcd.c

@@ -488,9 +488,6 @@ static int ehci_init(struct usb_hcd *hcd)
 	else					// N microframes cached
 		ehci->i_thresh = 2 + HCC_ISOC_THRES(hcc_params);
 
-	ehci->next_uframe = -1;
-	ehci->clock_frame = -1;
-
 	/*
 	 * dedicate a qh for the async ring head, since we couldn't unlink
 	 * a 'real' qh without stopping the async schedule [4.8].  use it

drivers/usb/host/ehci-sched.c

@@ -497,8 +497,6 @@ static void disable_periodic(struct ehci_hcd *ehci)
 	if (--ehci->periodic_count)
 		return;
 
-	ehci->next_uframe = -1;		/* the periodic schedule is empty */
-
 	/* Don't turn off the schedule until PSS is 1 */
 	ehci_poll_PSS(ehci);
 }
@@ -1220,7 +1218,7 @@ itd_urb_transaction (
 		if (likely(!list_empty(&stream->free_list))) {
 			itd = list_first_entry(&stream->free_list,
 					struct ehci_itd, itd_list);
-			if (itd->frame == ehci->clock_frame)
+			if (itd->frame == ehci->now_frame)
 				goto alloc_itd;
 			list_del (&itd->itd_list);
 			itd_dma = itd->itd_dma;
@@ -1492,7 +1490,7 @@ iso_stream_schedule (
 
 	/* Make sure scan_isoc() sees these */
 	if (ehci->isoc_count == 0)
-		ehci->next_uframe = now;
+		ehci->next_frame = now >> 3;
 	return 0;
 
  fail:
@@ -1666,11 +1664,8 @@ static void itd_link_urb(
  * (b) only this endpoint's completions submit URBs.  It seems some silicon
  * corrupts things if you reuse completed descriptors very quickly...
  */
-static unsigned
-itd_complete (
-	struct ehci_hcd	*ehci,
-	struct ehci_itd	*itd
-) {
+static bool itd_complete(struct ehci_hcd *ehci, struct ehci_itd *itd)
+{
 	struct urb				*urb = itd->urb;
 	struct usb_iso_packet_descriptor	*desc;
 	u32					t;
@@ -1678,7 +1673,7 @@ itd_complete (
 	int					urb_index = -1;
 	struct ehci_iso_stream			*stream = itd->stream;
 	struct usb_device			*dev;
-	unsigned				retval = false;
+	bool					retval = false;
 
 	/* for each uframe with a packet */
 	for (uframe = 0; uframe < 8; uframe++) {
@@ -1917,7 +1912,7 @@ sitd_urb_transaction (
 		if (likely(!list_empty(&stream->free_list))) {
 			sitd = list_first_entry(&stream->free_list,
 					 struct ehci_sitd, sitd_list);
-			if (sitd->frame == ehci->clock_frame)
+			if (sitd->frame == ehci->now_frame)
 				goto alloc_sitd;
 			list_del (&sitd->sitd_list);
 			sitd_dma = sitd->sitd_dma;
@@ -2071,18 +2066,15 @@ static void sitd_link_urb(
  * (b) only this endpoint's completions submit URBs.  It seems some silicon
  * corrupts things if you reuse completed descriptors very quickly...
  */
-static unsigned
-sitd_complete (
-	struct ehci_hcd		*ehci,
-	struct ehci_sitd	*sitd
-) {
+static bool sitd_complete(struct ehci_hcd *ehci, struct ehci_sitd *sitd)
+{
 	struct urb				*urb = sitd->urb;
 	struct usb_iso_packet_descriptor	*desc;
 	u32					t;
 	int					urb_index = -1;
 	struct ehci_iso_stream			*stream = sitd->stream;
 	struct usb_device			*dev;
-	unsigned				retval = false;
+	bool					retval = false;
 
 	urb_index = sitd->index;
 	desc = &urb->iso_frame_desc [urb_index];
@@ -2214,34 +2206,29 @@ static int sitd_submit (struct ehci_hcd *ehci, struct urb *urb,
 
 static void scan_isoc(struct ehci_hcd *ehci)
 {
-	unsigned	now_uframe, frame, clock, clock_frame, mod;
-	unsigned	modified;
-
-	mod = ehci->periodic_size << 3;
+	unsigned	uf, now_frame, frame;
+	unsigned	fmask = ehci->periodic_size - 1;
+	bool		modified, live;
 
 	/*
 	 * When running, scan from last scan point up to "now"
 	 * else clean up by scanning everything that's left.
 	 * Touches as few pages as possible:  cache-friendly.
 	 */
-	now_uframe = ehci->next_uframe;
 	if (ehci->rh_state >= EHCI_RH_RUNNING) {
-		clock = ehci_read_frame_index(ehci);
-		clock_frame = (clock >> 3) & (ehci->periodic_size - 1);
+		uf = ehci_read_frame_index(ehci);
+		now_frame = (uf >> 3) & fmask;
+		live = true;
 	} else  {
-		clock = now_uframe + mod - 1;
-		clock_frame = -1;
+		now_frame = (ehci->next_frame - 1) & fmask;
+		live = false;
 	}
-	ehci->clock_frame = clock_frame;
-	clock &= mod - 1;
-	clock_frame = clock >> 3;
+	ehci->now_frame = now_frame;
 
+	frame = ehci->next_frame;
 	for (;;) {
 		union ehci_shadow	q, *q_p;
 		__hc32			type, *hw_p;
-		unsigned		incomplete = false;
-
-		frame = now_uframe >> 3;
 
 restart:
 		/* scan each element in frame's queue for completions */
@@ -2249,13 +2236,9 @@ static void scan_isoc(struct ehci_hcd *ehci)
 		hw_p = &ehci->periodic [frame];
 		q.ptr = q_p->ptr;
 		type = Q_NEXT_TYPE(ehci, *hw_p);
-		modified = 0;
+		modified = false;
 
 		while (q.ptr != NULL) {
-			unsigned		uf;
-			int			live;
-
-			live = (ehci->rh_state >= EHCI_RH_RUNNING);
 			switch (hc32_to_cpu(ehci, type)) {
 			case Q_TYPE_ITD:
 				/* If this ITD is still active, leave it for
@@ -2263,7 +2246,7 @@ static void scan_isoc(struct ehci_hcd *ehci)
 				 * No need to check for activity unless the
 				 * frame is current.
 				 */
-				if (frame == clock_frame && live) {
+				if (frame == now_frame && live) {
 					rmb();
 					for (uf = 0; uf < 8; uf++) {
 						if (q.itd->hw_transaction[uf] &
@@ -2271,7 +2254,6 @@ static void scan_isoc(struct ehci_hcd *ehci)
 							break;
 					}
 					if (uf < 8) {
-						incomplete = true;
 						q_p = &q.itd->itd_next;
 						hw_p = &q.itd->hw_next;
 						type = Q_NEXT_TYPE(ehci,
@@ -2303,14 +2285,12 @@ static void scan_isoc(struct ehci_hcd *ehci)
 				 * No need to check for activity unless the
 				 * frame is current.
 				 */
-				if (((frame == clock_frame) ||
-				     (((frame + 1) & (ehci->periodic_size - 1))
-				      == clock_frame))
+				if (((frame == now_frame) ||
+				     (((frame + 1) & fmask) == now_frame))
 				    && live
 				    && (q.sitd->hw_results &
 					SITD_ACTIVE(ehci))) {
 
-					incomplete = true;
 					q_p = &q.sitd->sitd_next;
 					hw_p = &q.sitd->hw_next;
 					type = Q_NEXT_TYPE(ehci,
@@ -2347,50 +2327,14 @@ static void scan_isoc(struct ehci_hcd *ehci)
 			}
 
 			/* assume completion callbacks modify the queue */
-			if (unlikely (modified)) {
-				if (likely(ehci->isoc_count > 0))
+			if (unlikely(modified && ehci->isoc_count > 0))
 				goto restart;
-				/* short-circuit this scan */
-				now_uframe = clock;
-				break;
-			}
 		}
 
-		/* If we can tell we caught up to the hardware, stop now.
-		 * We can't advance our scan without collecting the ISO
-		 * transfers that are still pending in this frame.
-		 */
-		if (incomplete && ehci->rh_state >= EHCI_RH_RUNNING) {
-			ehci->next_uframe = now_uframe;
-			break;
-		}
-
-		// FIXME:  this assumes we won't get lapped when
-		// latencies climb; that should be rare, but...
-		// detect it, and just go all the way around.
-		// FLR might help detect this case, so long as latencies
-		// don't exceed periodic_size msec (default 1.024 sec).
-
-		// FIXME:  likewise assumes HC doesn't halt mid-scan
-
-		if (now_uframe == clock) {
-			unsigned	now;
-
-			if (ehci->rh_state < EHCI_RH_RUNNING
-					|| ehci->isoc_count == 0)
-				break;
-			ehci->next_uframe = now_uframe;
-			now = ehci_read_frame_index(ehci) & (mod - 1);
-			if (now_uframe == now)
+		/* Stop when we have reached the current frame */
+		if (frame == now_frame)
 			break;
-
-			/* rescan the rest of this frame, then ... */
-			clock = now;
-			clock_frame = clock >> 3;
-			ehci->clock_frame = clock_frame;
-		} else {
-			now_uframe++;
-			now_uframe &= mod - 1;
-		}
+		frame = (frame + 1) & fmask;
 	}
+	ehci->next_frame = now_frame;
 }

drivers/usb/host/ehci.h

@@ -141,19 +141,19 @@ struct ehci_hcd {			/* one per controller */
 	struct ehci_qh		*intr_unlink;
 	struct ehci_qh		*intr_unlink_last;
 	unsigned		intr_unlink_cycle;
-	int			next_uframe;	/* scan periodic, start here */
+	unsigned		now_frame;	/* frame from HC hardware */
+	unsigned		next_frame;	/* scan periodic, start here */
 	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 clock_frame was still active */
+	/* 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;
-	unsigned		clock_frame;
 
 	/* per root hub port */
 	unsigned long		reset_done [EHCI_MAX_ROOT_PORTS];