usb: dwc2: host: Manage frame nums better in scheduler

The dwc2 scheduler (contained in hcd_queue.c) was a bit confusing in the
way it initted / kept track of which frames a QH was going to be active
in.  Let's clean things up a little bit in preparation for a rewrite of
the microframe scheduler.

Specifically:
* Old code would pick a frame number in dwc2_qh_init() and would try to
  pick it "in a slightly future (micro)frame".  As far as I can tell the
  reason for this was that there was a delay between dwc2_qh_init() and
  when we actually wanted to dwc2_hcd_qh_add().  ...but apparently this
  attempt to be slightly in the future wasn't enough because
  dwc2_hcd_qh_add() then had code to reset things if the frame _wasn't_
  in the future.  There's no reason not to just pick the frame later.
  For non-periodic QH we now pick the frame in dwc2_hcd_qh_add().  For
  periodic QH we pick the frame at dwc2_schedule_periodic() time.
* The old "dwc2_qh_init() actually assigned to "hsotg->frame_number".
  This doesn't seem like a great idea since that variable is supposed to
  be used to keep track of which SOF the interrupt handler has seen.
  Let's be clean: anyone who wants the current frame number (instead of
  the one as of the last interrupt) should ask for it.
* The old code wasn't terribly consistent about trying to use the frame
  that the microframe scheduler assigned to it.  In
  dwc2_sched_periodic_split() when it was scheduling the first frame it
  always "ORed" in 0x7 (!).  Since the frame goes on the wire 1 uFrame
  after next_active_frame it meant that the SSPLIT would always try for
  uFrame 0 and the transaction would happen on the low speed bus during
  uFrame 1.  This is irregardless of what the microframe scheduler
  said.
* The old code assumed it would get called to schedule the next in a
  periodic split very quickly.  That is if next_active_frame was
  0 (transfer on wire in uFrame 1) it assumed it was getting called to
  schedule the next uFrame during uFrame 1 too (so it could queue
  something up for uFrame 2).  It should be possible to actually queue
  something up for uFrame 2 while in uFrame 2 (AKA queue up ASAP).  To
  do this, code needs to look at the previously scheduled frame when
  deciding when to next be active, not look at the current frame number.
* If there was no microframe scheduler, the old code would check for
  whether we should be active using "qh->next_active_frame ==
  frame_number".  This seemed like a race waiting to happen.  ...plus
  there's no way that you wouldn't want to schedule if next_active_frame
  was actually less than frame number.

Note that this change doesn't make 100% sense on its own since it's
expecting some sanity in the frame numbers assigned by the microframe
scheduler and (as per the future patch which rewries it) I think that
the current microframe scheduler is quite insane.  However, it seems
like splitting this up from the microframe scheduler patch makes things
into smaller chunks and hopefully adds to clarity rather than reduces
it.  The two patches could certainly be squashed.  Not that in the very
least, I don't see any obvious bad behavior introduced with just this
patch.

I've attempted to keep the config parameter to disable the microframe
scheduler in tact in this change, though I'm not sure it's worth it.
Obviously the code is touched a lot so it's possible I regressed
something when the microframe scheduler is disabled, though I did some
basic testing and it seemed to work OK.  I'm still not 100% sure why you
wouldn't want the microframe scheduler (presuming it works), so maybe a
future patch (or a future version of this patch?) could remove that
parameter.
Acked-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

drivers/usb/dwc2/hcd.h

@@ -244,8 +244,11 @@ enum dwc2_transaction_type {
  *                      the bus.  We'll move the qh to active here.  If the
  *                      host is in high speed mode this will be a uframe.  If
  *                      the host is in low speed mode this will be a full frame.
+ * @start_active_frame: If we are partway through a split transfer, this will be
+ *			what next_active_frame was when we started.  Otherwise
+ *			it should always be the same as next_active_frame.
+ * @assigned_uframe:    The uframe (0 -7) assigned by dwc2_find_uframe().
  * @frame_usecs:        Internal variable used by the microframe scheduler
- * @start_split_frame:  (Micro)frame at which last start split was initialized
  * @ntd:                Actual number of transfer descriptors in a list
  * @qtd_list:           List of QTDs for this QH
  * @channel:            Host channel currently processing transfers for this QH
@@ -279,8 +282,9 @@ struct dwc2_qh {
 	u16 host_us;
 	u16 host_interval;
 	u16 next_active_frame;
+	u16 start_active_frame;
+	u16 assigned_uframe;
 	u16 frame_usecs[8];
-	u16 start_split_frame;
 	u16 ntd;
 	struct list_head qtd_list;
 	struct dwc2_host_chan *channel;
@@ -746,7 +750,7 @@ do {									\
 	_qtd_ = list_entry((_qh_)->qtd_list.next, struct dwc2_qtd,	\
 			   qtd_list_entry);				\
 	if (usb_pipeint(_qtd_->urb->pipe) &&				\
-	    (_qh_)->start_split_frame != 0 && !_qtd_->complete_split) {	\
+	    (_qh_)->start_active_frame != 0 && !_qtd_->complete_split) { \
 		_hfnum_.d32 = dwc2_readl((_hcd_)->regs + HFNUM);	\
 		switch (_hfnum_.b.frnum & 0x7) {			\
 		case 7:							\

drivers/usb/dwc2/hcd_queue.c

@@ -38,6 +38,7 @@
  * This file contains the functions to manage Queue Heads and Queue
  * Transfer Descriptors for Host mode
  */
+#include <linux/gcd.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/spinlock.h>
@@ -244,6 +245,96 @@ static int dwc2_find_uframe(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh)
 	return ret;
 }
 
+/**
+ * dwc2_pick_first_frame() - Choose 1st frame for qh that's already scheduled
+ *
+ * Takes a qh that has already been scheduled (which means we know we have the
+ * bandwdith reserved for us) and set the next_active_frame and the
+ * start_active_frame.
+ *
+ * This is expected to be called on qh's that weren't previously actively
+ * running.  It just picks the next frame that we can fit into without any
+ * thought about the past.
+ *
+ * @hsotg: The HCD state structure for the DWC OTG controller
+ * @qh:    QH for a periodic endpoint
+ *
+ */
+static void dwc2_pick_first_frame(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh)
+{
+	u16 frame_number;
+	u16 earliest_frame;
+	u16 next_active_frame;
+	u16 interval;
+
+	/*
+	 * Use the real frame number rather than the cached value as of the
+	 * last SOF to give us a little extra slop.
+	 */
+	frame_number = dwc2_hcd_get_frame_number(hsotg);
+
+	/*
+	 * We wouldn't want to start any earlier than the next frame just in
+	 * case the frame number ticks as we're doing this calculation.
+	 *
+	 * NOTE: if we could quantify how long till we actually get scheduled
+	 * we might be able to avoid the "+ 1" by looking at the upper part of
+	 * HFNUM (the FRREM field).  For now we'll just use the + 1 though.
+	 */
+	earliest_frame = dwc2_frame_num_inc(frame_number, 1);
+	next_active_frame = earliest_frame;
+
+	/* Get the "no microframe schduler" out of the way... */
+	if (hsotg->core_params->uframe_sched <= 0) {
+		if (qh->do_split)
+			/* Splits are active at microframe 0 minus 1 */
+			next_active_frame |= 0x7;
+		goto exit;
+	}
+
+	/* Adjust interval as per high speed schedule which has 8 uFrame */
+	interval = gcd(qh->host_interval, 8);
+
+	/*
+	 * We know interval must divide (HFNUM_MAX_FRNUM + 1) now that we've
+	 * done the gcd(), so it's safe to move to the beginning of the current
+	 * interval like this.
+	 *
+	 * After this we might be before earliest_frame, but don't worry,
+	 * we'll fix it...
+	 */
+	next_active_frame = (next_active_frame / interval) * interval;
+
+	/*
+	 * Actually choose to start at the frame number we've been
+	 * scheduled for.
+	 */
+	next_active_frame = dwc2_frame_num_inc(next_active_frame,
+					       qh->assigned_uframe);
+
+	/*
+	 * We actually need 1 frame before since the next_active_frame is
+	 * the frame number we'll be put on the ready list and we won't be on
+	 * the bus until 1 frame later.
+	 */
+	next_active_frame = dwc2_frame_num_dec(next_active_frame, 1);
+
+	/*
+	 * By now we might actually be before the earliest_frame.  Let's move
+	 * up intervals until we're not.
+	 */
+	while (dwc2_frame_num_gt(earliest_frame, next_active_frame))
+		next_active_frame = dwc2_frame_num_inc(next_active_frame,
+						       interval);
+
+exit:
+	qh->next_active_frame = next_active_frame;
+	qh->start_active_frame = next_active_frame;
+
+	dwc2_sch_vdbg(hsotg, "QH=%p First fn=%04x nxt=%04x\n",
+		     qh, frame_number, qh->next_active_frame);
+}
+
 /**
  * dwc2_do_reserve() - Make a periodic reservation
  *
@@ -260,25 +351,9 @@ static int dwc2_do_reserve(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh)
 	int status;
 
 	if (hsotg->core_params->uframe_sched > 0) {
-		int frame = -1;
-
 		status = dwc2_find_uframe(hsotg, qh);
-		if (status == 0)
-			frame = 7;
-		else if (status > 0)
-			frame = status - 1;
-
-		/* Set the new frame up */
-		if (frame >= 0) {
-			qh->next_active_frame &= ~0x7;
-			qh->next_active_frame |= (frame & 7);
-			dwc2_sch_dbg(hsotg,
-				     "QH=%p sched_p nxt=%04x, uf=%d\n",
-				     qh, qh->next_active_frame, frame);
-		}
-
-		if (status > 0)
-			status = 0;
+		if (status >= 0)
+			qh->assigned_uframe = status;
 	} else {
 		status = dwc2_periodic_channel_available(hsotg);
 		if (status) {
@@ -305,6 +380,8 @@ static int dwc2_do_reserve(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh)
 	/* Update claimed usecs per (micro)frame */
 	hsotg->periodic_usecs += qh->host_us;
 
+	dwc2_pick_first_frame(hsotg, qh);
+
 	return 0;
 }
 
@@ -460,6 +537,16 @@ static int dwc2_schedule_periodic(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh)
 		status = dwc2_do_reserve(hsotg, qh);
 		if (status)
 			return status;
+	} else {
+		/*
+		 * It might have been a while, so make sure that frame_number
+		 * is still good.  Note: we could also try to use the similar
+		 * dwc2_next_periodic_start() but that schedules much more
+		 * tightly and we might need to hurry and queue things up.
+		 */
+		if (dwc2_frame_num_le(qh->next_active_frame,
+				      hsotg->frame_number))
+			dwc2_pick_first_frame(hsotg, qh);
 	}
 
 	qh->unreserve_pending = 0;
@@ -520,7 +607,6 @@ static void dwc2_deschedule_periodic(struct dwc2_hsotg *hsotg,
  * @urb:   Holds the information about the device/endpoint needed to initialize
  *         the QH
  */
-#define SCHEDULE_SLOP 10
 static void dwc2_qh_init(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh,
 			 struct dwc2_hcd_urb *urb)
 {
@@ -569,11 +655,6 @@ static void dwc2_qh_init(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh,
 			      qh->ep_type == USB_ENDPOINT_XFER_ISOC,
 			      bytecount));
 
-		/* Ensure frame_number corresponds to the reality */
-		hsotg->frame_number = dwc2_hcd_get_frame_number(hsotg);
-		/* Start in a slightly future (micro)frame */
-		qh->next_active_frame = dwc2_frame_num_inc(hsotg->frame_number,
-						     SCHEDULE_SLOP);
 		qh->host_interval = urb->interval;
 		dwc2_sch_dbg(hsotg, "QH=%p init nxt=%04x, fn=%04x, int=%#x\n",
 			     qh, qh->next_active_frame, hsotg->frame_number,
@@ -589,8 +670,6 @@ static void dwc2_qh_init(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh,
 		    (dev_speed == USB_SPEED_LOW ||
 		     dev_speed == USB_SPEED_FULL)) {
 			qh->host_interval *= 8;
-			qh->next_active_frame |= 0x7;
-			qh->start_split_frame = qh->next_active_frame;
 			dwc2_sch_dbg(hsotg,
 				     "QH=%p init*8 nxt=%04x, fn=%04x, int=%#x\n",
 				     qh, qh->next_active_frame,
@@ -738,22 +817,12 @@ int dwc2_hcd_qh_add(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh)
 		/* QH already in a schedule */
 		return 0;
 
-	if (!dwc2_frame_num_le(qh->next_active_frame, hsotg->frame_number) &&
-			!hsotg->frame_number) {
-		u16 new_frame;
-
-		dev_dbg(hsotg->dev,
-				"reset frame number counter\n");
-		new_frame = dwc2_frame_num_inc(hsotg->frame_number,
-				SCHEDULE_SLOP);
-
-		dwc2_sch_vdbg(hsotg, "QH=%p reset nxt=%04x=>%04x\n",
-			      qh, qh->next_active_frame, new_frame);
-		qh->next_active_frame = new_frame;
-	}
-
 	/* Add the new QH to the appropriate schedule */
 	if (dwc2_qh_is_non_per(qh)) {
+		/* Schedule right away */
+		qh->start_active_frame = hsotg->frame_number;
+		qh->next_active_frame = qh->start_active_frame;
+
 		/* Always start in inactive schedule */
 		list_add_tail(&qh->qh_list_entry,
 			      &hsotg->non_periodic_sched_inactive);
@@ -807,46 +876,145 @@ void dwc2_hcd_qh_unlink(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh)
 	}
 }
 
-/*
- * Schedule the next continuing periodic split transfer
+/**
+ * dwc2_next_for_periodic_split() - Set next_active_frame midway thru a split.
+ *
+ * This is called for setting next_active_frame for periodic splits for all but
+ * the first packet of the split.  Confusing?  I thought so...
+ *
+ * Periodic splits are single low/full speed transfers that we end up splitting
+ * up into several high speed transfers.  They always fit into one full (1 ms)
+ * frame but might be split over several microframes (125 us each).  We to put
+ * each of the parts on a very specific high speed frame.
+ *
+ * This function figures out where the next active uFrame needs to be.
+ *
+ * @hsotg:        The HCD state structure
+ * @qh:           QH for the periodic transfer.
+ * @frame_number: The current frame number.
+ *
+ * Return: number missed by (or 0 if we didn't miss).
  */
-static void dwc2_sched_periodic_split(struct dwc2_hsotg *hsotg,
-				      struct dwc2_qh *qh, u16 frame_number,
-				      int sched_next_periodic_split)
+static int dwc2_next_for_periodic_split(struct dwc2_hsotg *hsotg,
+					 struct dwc2_qh *qh, u16 frame_number)
 {
-	u16 incr;
 	u16 old_frame = qh->next_active_frame;
+	u16 prev_frame_number = dwc2_frame_num_dec(frame_number, 1);
+	int missed = 0;
+	u16 incr;
+
+	/*
+	 * Basically: increment 1 normally, but 2 right after the start split
+	 * (except for ISOC out).
+	 */
+	if (old_frame == qh->start_active_frame &&
+	    !(qh->ep_type == USB_ENDPOINT_XFER_ISOC && !qh->ep_is_in))
+		incr = 2;
+	else
+		incr = 1;
+
+	qh->next_active_frame = dwc2_frame_num_inc(old_frame, incr);
 
-	if (sched_next_periodic_split) {
+	/*
+	 * Note that it's OK for frame_number to be 1 frame past
+	 * next_active_frame.  Remember that next_active_frame is supposed to
+	 * be 1 frame _before_ when we want to be scheduled.  If we're 1 frame
+	 * past it just means schedule ASAP.
+	 *
+	 * It's _not_ OK, however, if we're more than one frame past.
+	 */
+	if (dwc2_frame_num_gt(prev_frame_number, qh->next_active_frame)) {
+		/*
+		 * OOPS, we missed.  That's actually pretty bad since
+		 * the hub will be unhappy; try ASAP I guess.
+		 */
+		missed = dwc2_frame_num_dec(prev_frame_number,
+					    qh->next_active_frame);
 		qh->next_active_frame = frame_number;
-		incr = dwc2_frame_num_inc(qh->start_split_frame, 1);
-		if (dwc2_frame_num_le(frame_number, incr)) {
-			/*
-			 * Allow one frame to elapse after start split
-			 * microframe before scheduling complete split, but
-			 * DON'T if we are doing the next start split in the
-			 * same frame for an ISOC out
-			 */
-			if (qh->ep_type != USB_ENDPOINT_XFER_ISOC ||
-			    qh->ep_is_in != 0) {
-				qh->next_active_frame = dwc2_frame_num_inc(
-					qh->next_active_frame, 1);
-			}
-		}
-	} else {
-		qh->next_active_frame =
-			dwc2_frame_num_inc(qh->start_split_frame,
-					   qh->host_interval);
-		if (dwc2_frame_num_le(qh->next_active_frame, frame_number))
-			qh->next_active_frame = frame_number;
-		qh->next_active_frame |= 0x7;
-		qh->start_split_frame = qh->next_active_frame;
 	}
 
-	dwc2_sch_vdbg(hsotg, "QH=%p next(%d) fn=%04x, nxt=%04x=>%04x (%+d)\n",
-		      qh, sched_next_periodic_split, frame_number, old_frame,
-		      qh->next_active_frame,
-		      dwc2_frame_num_dec(qh->next_active_frame, old_frame));
+	return missed;
+}
+
+/**
+ * dwc2_next_periodic_start() - Set next_active_frame for next transfer start
+ *
+ * This is called for setting next_active_frame for a periodic transfer for
+ * all cases other than midway through a periodic split.  This will also update
+ * start_active_frame.
+ *
+ * Since we _always_ keep start_active_frame as the start of the previous
+ * transfer this is normally pretty easy: we just add our interval to
+ * start_active_frame and we've got our answer.
+ *
+ * The tricks come into play if we miss.  In that case we'll look for the next
+ * slot we can fit into.
+ *
+ * @hsotg:        The HCD state structure
+ * @qh:           QH for the periodic transfer.
+ * @frame_number: The current frame number.
+ *
+ * Return: number missed by (or 0 if we didn't miss).
+ */
+static int dwc2_next_periodic_start(struct dwc2_hsotg *hsotg,
+				     struct dwc2_qh *qh, u16 frame_number)
+{
+	int missed = 0;
+	u16 interval = qh->host_interval;
+	u16 prev_frame_number = dwc2_frame_num_dec(frame_number, 1);
+
+	qh->start_active_frame = dwc2_frame_num_inc(qh->start_active_frame,
+						    interval);
+
+	/*
+	 * The dwc2_frame_num_gt() function used below won't work terribly well
+	 * with if we just incremented by a really large intervals since the
+	 * frame counter only goes to 0x3fff.  It's terribly unlikely that we
+	 * will have missed in this case anyway.  Just go to exit.  If we want
+	 * to try to do better we'll need to keep track of a bigger counter
+	 * somewhere in the driver and handle overflows.
+	 */
+	if (interval >= 0x1000)
+		goto exit;
+
+	/*
+	 * Test for misses, which is when it's too late to schedule.
+	 *
+	 * A few things to note:
+	 * - We compare against prev_frame_number since start_active_frame
+	 *   and next_active_frame are always 1 frame before we want things
+	 *   to be active and we assume we can still get scheduled in the
+	 *   current frame number.
+	 * - Some misses are expected.  Specifically, in order to work
+	 *   perfectly dwc2 really needs quite spectacular interrupt latency
+	 *   requirements.  It needs to be able to handle its interrupts
+	 *   completely within 125 us of them being asserted. That not only
+	 *   means that the dwc2 interrupt handler needs to be fast but it
+	 *   means that nothing else in the system has to block dwc2 for a long
+	 *   time.  We can help with the dwc2 parts of this, but it's hard to
+	 *   guarantee that a system will have interrupt latency < 125 us, so
+	 *   we have to be robust to some misses.
+	 */
+	if (dwc2_frame_num_gt(prev_frame_number, qh->start_active_frame)) {
+		u16 ideal_start = qh->start_active_frame;
+
+		/* Adjust interval as per gcd with plan length. */
+		interval = gcd(interval, 8);
+
+		do {
+			qh->start_active_frame = dwc2_frame_num_inc(
+				qh->start_active_frame, interval);
+		} while (dwc2_frame_num_gt(prev_frame_number,
+					   qh->start_active_frame));
+
+		missed = dwc2_frame_num_dec(qh->start_active_frame,
+					    ideal_start);
+	}
+
+exit:
+	qh->next_active_frame = qh->start_active_frame;
+
+	return missed;
 }
 
 /*
@@ -865,7 +1033,9 @@ static void dwc2_sched_periodic_split(struct dwc2_hsotg *hsotg,
 void dwc2_hcd_qh_deactivate(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh,
 			    int sched_next_periodic_split)
 {
+	u16 old_frame = qh->next_active_frame;
 	u16 frame_number;
+	int missed;
 
 	if (dbg_qh(qh))
 		dev_vdbg(hsotg->dev, "%s()\n", __func__);
@@ -878,30 +1048,39 @@ void dwc2_hcd_qh_deactivate(struct dwc2_hsotg *hsotg, struct dwc2_qh *qh,
 		return;
 	}
 
+	/*
+	 * Use the real frame number rather than the cached value as of the
+	 * last SOF just to get us a little closer to reality.  Note that
+	 * means we don't actually know if we've already handled the SOF
+	 * interrupt for this frame.
+	 */
 	frame_number = dwc2_hcd_get_frame_number(hsotg);
 
-	if (qh->do_split) {
-		dwc2_sched_periodic_split(hsotg, qh, frame_number,
-					  sched_next_periodic_split);
-	} else {
-		qh->next_active_frame = dwc2_frame_num_inc(
-			qh->next_active_frame, qh->host_interval);
-		if (dwc2_frame_num_le(qh->next_active_frame, frame_number))
-			qh->next_active_frame = frame_number;
-	}
+	if (sched_next_periodic_split)
+		missed = dwc2_next_for_periodic_split(hsotg, qh, frame_number);
+	else
+		missed = dwc2_next_periodic_start(hsotg, qh, frame_number);
+
+	dwc2_sch_vdbg(hsotg,
+		     "QH=%p next(%d) fn=%04x, sch=%04x=>%04x (%+d) miss=%d %s\n",
+		     qh, sched_next_periodic_split, frame_number, old_frame,
+		     qh->next_active_frame,
+		     dwc2_frame_num_dec(qh->next_active_frame, old_frame),
+		missed, missed ? "MISS" : "");
 
 	if (list_empty(&qh->qtd_list)) {
 		dwc2_hcd_qh_unlink(hsotg, qh);
 		return;
 	}
+
 	/*
 	 * Remove from periodic_sched_queued and move to
 	 * appropriate queue
+	 *
+	 * Note: we purposely use the frame_number from the "hsotg" structure
+	 * since we know SOF interrupt will handle future frames.
 	 */
-	if ((hsotg->core_params->uframe_sched > 0 &&
-	     dwc2_frame_num_le(qh->next_active_frame, frame_number)) ||
-	    (hsotg->core_params->uframe_sched <= 0 &&
-	     qh->next_active_frame == frame_number))
+	if (dwc2_frame_num_le(qh->next_active_frame, hsotg->frame_number))
 		list_move_tail(&qh->qh_list_entry,
 			       &hsotg->periodic_sched_ready);
 	else