1 files changed, 18 insertions, 1 deletions

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index b520b37c0f36..407d33fb5e84 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -242,10 +242,27 @@ static int room_on_ring(struct xhci_hcd *xhci, struct xhci_ring *ring,
         int i;
         union xhci_trb *enq = ring->enqueue;
         struct xhci_segment *enq_seg = ring->enq_seg;
+        struct xhci_segment *cur_seg;
+        unsigned int left_on_ring;
 
         /* Check if ring is empty */
-        if (enq == ring->dequeue)
+        if (enq == ring->dequeue) {
+                /* Can't use link trbs */
+                left_on_ring = TRBS_PER_SEGMENT - 1;
+                for (cur_seg = enq_seg->next; cur_seg != enq_seg;
+                                cur_seg = cur_seg->next)
+                        left_on_ring += TRBS_PER_SEGMENT - 1;
+
+                /* Always need one TRB free in the ring. */
+                left_on_ring -= 1;
+                if (num_trbs > left_on_ring) {
+                        xhci_warn(xhci, "Not enough room on ring; "
+                                        "need %u TRBs, %u TRBs left\n",
+                                        num_trbs, left_on_ring);
+                        return 0;
+                }
                 return 1;
+        }
         /* Make sure there's an extra empty TRB available */
         for (i = 0; i <= num_trbs; ++i) {
                 if (enq == ring->dequeue)