Since ring->index points to the next free slot, once we reach index zero

we know that the last non-link TRB has been written and we can look at
the flags to set the chain bit in the link TRB.  Since we will now toggle
the cycle bit on the first TRB of a ring, set it on the ring reset.

Tested by jcs@, jsg@ and visa@
"commit it" jcs@

1 files changed, 17 insertions, 14 deletions

diff --git a/sys/dev/usb/xhci.c b/sys/dev/usb/xhci.c
index efa46ad674a..6b01165672b 100644
--- a/sys/dev/usb/xhci.c
+++ b/sys/dev/usb/xhci.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: xhci.c,v 1.92 2019/02/27 05:22:37 patrick Exp $ */
+/* $OpenBSD: xhci.c,v 1.93 2019/03/01 19:15:59 patrick Exp $ */
 
 /*
  * Copyright (c) 2014-2015 Martin Pieuchot
@@ -1551,7 +1551,8 @@ xhci_ring_reset(struct xhci_softc *sc, struct xhci_ring *ring)
 		struct xhci_trb *trb = &ring->trbs[ring->ntrb - 1];
 
 		trb->trb_paddr = htole64(ring->dma.paddr);
-		trb->trb_flags = htole32(XHCI_TRB_TYPE_LINK | XHCI_TRB_LINKSEG);
+		trb->trb_flags = htole32(XHCI_TRB_TYPE_LINK | XHCI_TRB_LINKSEG |
+		    XHCI_TRB_CYCLE);
 		bus_dmamap_sync(ring->dma.tag, ring->dma.map, 0, size,
 		    BUS_DMASYNC_PREWRITE);
 	} else
@@ -1586,27 +1587,21 @@ xhci_ring_consume(struct xhci_softc *sc, struct xhci_ring *ring)
 struct xhci_trb*
 xhci_ring_produce(struct xhci_softc *sc, struct xhci_ring *ring)
 {
-	struct xhci_trb *trb = &ring->trbs[ring->index];
-	int oidx;
+	struct xhci_trb *lnk, *trb;
 
 	KASSERT(ring->index < ring->ntrb);
 
-	bus_dmamap_sync(ring->dma.tag, ring->dma.map, TRBOFF(ring, trb),
-	    sizeof(struct xhci_trb), BUS_DMASYNC_POSTREAD |
-	    BUS_DMASYNC_POSTWRITE);
-
-	oidx = ring->index++;
-
-	/* Toggle cycle state of the link TRB and skip it. */
-	if (ring->index == (ring->ntrb - 1)) {
-		struct xhci_trb *lnk = &ring->trbs[ring->index];
+	/* Setup the link TRB after the previous TRB is done. */
+	if (ring->index == 0) {
+		lnk = &ring->trbs[ring->ntrb - 1];
+		trb = &ring->trbs[ring->ntrb - 2];
 
 		bus_dmamap_sync(ring->dma.tag, ring->dma.map, TRBOFF(ring, lnk),
 		    sizeof(struct xhci_trb), BUS_DMASYNC_POSTREAD |
 		    BUS_DMASYNC_POSTWRITE);
 
 		lnk->trb_flags &= htole32(~XHCI_TRB_CHAIN);
-		if (letoh32(ring->trbs[oidx].trb_flags) & XHCI_TRB_CHAIN)
+		if (letoh32(trb->trb_flags) & XHCI_TRB_CHAIN)
 			lnk->trb_flags |= htole32(XHCI_TRB_CHAIN);
 
 		bus_dmamap_sync(ring->dma.tag, ring->dma.map, TRBOFF(ring, lnk),
@@ -1616,7 +1611,15 @@ xhci_ring_produce(struct xhci_softc *sc, struct xhci_ring *ring)
 
 		bus_dmamap_sync(ring->dma.tag, ring->dma.map, TRBOFF(ring, lnk),
 		    sizeof(struct xhci_trb), BUS_DMASYNC_PREWRITE);
+	}
 
+	trb = &ring->trbs[ring->index++];
+	bus_dmamap_sync(ring->dma.tag, ring->dma.map, TRBOFF(ring, trb),
+	    sizeof(struct xhci_trb), BUS_DMASYNC_POSTREAD |
+	    BUS_DMASYNC_POSTWRITE);
+
+	/* Toggle cycle state of the link TRB and skip it. */
+	if (ring->index == (ring->ntrb - 1)) {
 		ring->index = 0;
 		ring->toggle ^= 1;
 	}