1 files changed, 52 insertions, 2 deletions

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 1e2f3f495843..53c2e296467f 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -2973,8 +2973,58 @@ static int prepare_ring(struct xhci_hcd *xhci, struct xhci_ring *ep_ring,
         }
 
         while (1) {
-                if (room_on_ring(xhci, ep_ring, num_trbs))
-                        break;
+                if (room_on_ring(xhci, ep_ring, num_trbs)) {
+                        union xhci_trb *trb = ep_ring->enqueue;
+                        unsigned int usable = ep_ring->enq_seg->trbs +
+                                        TRBS_PER_SEGMENT - 1 - trb;
+                        u32 nop_cmd;
+
+                        /*
+                         * Section 4.11.7.1 TD Fragments states that a link
+                         * TRB must only occur at the boundary between
+                         * data bursts (eg 512 bytes for 480M).
+                         * While it is possible to split a large fragment
+                         * we don't know the size yet.
+                         * Simplest solution is to fill the trb before the
+                         * LINK with nop commands.
+                         */
+                        if (num_trbs == 1 || num_trbs <= usable || usable == 0)
+                                break;
+
+                        if (ep_ring->type != TYPE_BULK)
+                                /*
+                                 * While isoc transfers might have a buffer that
+                                 * crosses a 64k boundary it is unlikely.
+                                 * Since we can't add NOPs without generating
+                                 * gaps in the traffic just hope it never
+                                 * happens at the end of the ring.
+                                 * This could be fixed by writing a LINK TRB
+                                 * instead of the first NOP - however the
+                                 * TRB_TYPE_LINK_LE32() calls would all need
+                                 * changing to check the ring length.
+                                 */
+                                break;
+
+                        if (num_trbs >= TRBS_PER_SEGMENT) {
+                                xhci_err(xhci, "Too many fragments %d, max %d\n",
+                                                num_trbs, TRBS_PER_SEGMENT - 1);
+                                return -ENOMEM;
+                        }
+
+                        nop_cmd = cpu_to_le32(TRB_TYPE(TRB_TR_NOOP) |
+                                        ep_ring->cycle_state);
+                        ep_ring->num_trbs_free -= usable;
+                        do {
+                                trb->generic.field[0] = 0;
+                                trb->generic.field[1] = 0;
+                                trb->generic.field[2] = 0;
+                                trb->generic.field[3] = nop_cmd;
+                                trb++;
+                        } while (--usable);
+                        ep_ring->enqueue = trb;
+                        if (room_on_ring(xhci, ep_ring, num_trbs))
+                                break;
+                }
 
                 if (ep_ring == xhci->cmd_ring) {
                         xhci_err(xhci, "Do not support expand command ring\n");