[openib-general] [PATCH] mthca: fix posting lists of 256 entries for tavor

[Michael S. Tsirkin]

If we post a list of length 256 exactly, nreq in doorbell gets set to 256 which
is wrong: should be encoded by 0. This is because we only zero it out on next
WR, which may not be there.  The solution is to ring the doorbell after posting
a WQE, not before posting the next one.

Signed-off-by: Michael S. Tsirkin <mst at mellanox.co.il>

Index: linux-2.6.16/drivers/infiniband/hw/mthca/mthca_qp.c
===================================================================
--- linux-2.6.16/drivers/infiniband/hw/mthca/mthca_qp.c	(revision 7261)
+++ linux-2.6.16/drivers/infiniband/hw/mthca/mthca_qp.c	(working copy)
@@ -1725,23 +1725,7 @@
 
 	ind = qp->rq.next_ind;
 
-	for (nreq = 0; wr; ++nreq, wr = wr->next) {
-		if (unlikely(nreq == MTHCA_TAVOR_MAX_WQES_PER_RECV_DB)) {
-			nreq = 0;
-
-			doorbell[0] = cpu_to_be32((qp->rq.next_ind << qp->rq.wqe_shift) | size0);
-			doorbell[1] = cpu_to_be32(qp->qpn << 8);
-
-			wmb();
-
-			mthca_write64(doorbell,
-				      dev->kar + MTHCA_RECEIVE_DOORBELL,
-				      MTHCA_GET_DOORBELL_LOCK(&dev->doorbell_lock));
-
-			qp->rq.head += MTHCA_TAVOR_MAX_WQES_PER_RECV_DB;
-			size0 = 0;
-		}
-
+	for (nreq = 0; wr; wr = wr->next) {
 		if (mthca_wq_overflow(&qp->rq, nreq, qp->ibqp.recv_cq)) {
 			mthca_err(dev, "RQ %06x full (%u head, %u tail,"
 					" %d max, %d nreq)\n", qp->qpn,
@@ -1795,6 +1779,22 @@
 		++ind;
 		if (unlikely(ind >= qp->rq.max))
 			ind -= qp->rq.max;
+
+		if (unlikely(++nreq == MTHCA_TAVOR_MAX_WQES_PER_RECV_DB)) {
+			nreq = 0;
+
+			doorbell[0] = cpu_to_be32((qp->rq.next_ind << qp->rq.wqe_shift) | size0);
+			doorbell[1] = cpu_to_be32(qp->qpn << 8);
+
+			wmb();
+
+			mthca_write64(doorbell,
+				      dev->kar + MTHCA_RECEIVE_DOORBELL,
+				      MTHCA_GET_DOORBELL_LOCK(&dev->doorbell_lock));
+
+			qp->rq.head += MTHCA_TAVOR_MAX_WQES_PER_RECV_DB;
+			size0 = 0;
+		}
 	}
 
 out:

-- 
MST