xHCI: count free TRBs on transfer ring

In the past, the room_on_ring() check was implemented by walking all over
the ring, which is wasteful and complicated.

Count the number of free TRBs instead. The free TRBs number should be
updated when enqueue/dequeue pointer is updated, or upon the completion
of a set dequeue pointer command.

Signed-off-by: Andiry Xu <andiry.xu@amd.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Tested-by: Paul Zimmerman <Paul.Zimmerman@synopsys.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
index bdea4de867b4..212012c97df3 100644
--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -135,6 +135,12 @@ static void xhci_initialize_ring_info(struct xhci_ring *ring)
         /* Not necessary for new rings, but needed for re-initialized rings */
         ring->enq_updates = 0;
         ring->deq_updates = 0;
+
+        /*
+         * Each segment has a link TRB, and leave an extra TRB for SW
+         * accounting purpose
+         */
+        ring->num_trbs_free = ring->num_segs * (TRBS_PER_SEGMENT - 1) - 1;
 }
 
 /**