IB/mthca: Use mmiowb after doorbell ring

We discovered a problem when running IPoIB applications on multiple
CPUs on an Altix system. Many messages such as:

ib_mthca 0002:01:00.0: SQ 000014 full (19941644 head, 19941707 tail, 64 max, 0 nreq)

appear in syslog, and the driver wedges up.

Apparently this is because writes to the doorbells from different CPUs
reach the device out of order. The following patch adds mmiowb() calls
after doorbell rings to ensure the doorbell writes are ordered.

Signed-off-by: Arthur Kepner <akepner@sgi.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/drivers/infiniband/hw/mthca/mthca_qp.c b/drivers/infiniband/hw/mthca/mthca_qp.c
index 5e5c58b9920b..6a7822e0fc19 100644
--- a/drivers/infiniband/hw/mthca/mthca_qp.c
+++ b/drivers/infiniband/hw/mthca/mthca_qp.c
@@ -39,6 +39,8 @@
 #include <linux/string.h>
 #include <linux/slab.h>
 
+#include <asm/io.h>
+
 #include <rdma/ib_verbs.h>
 #include <rdma/ib_cache.h>
 #include <rdma/ib_pack.h>
@@ -1732,6 +1734,11 @@ out:
                 mthca_write64(doorbell,
                               dev->kar + MTHCA_SEND_DOORBELL,
                               MTHCA_GET_DOORBELL_LOCK(&dev->doorbell_lock));
+                /*
+                 * Make sure doorbells don't leak out of SQ spinlock
+                 * and reach the HCA out of order:
+                 */
+                mmiowb();
         }
 
         qp->sq.next_ind = ind;
@@ -1851,6 +1858,12 @@ out:
         qp->rq.next_ind = ind;
         qp->rq.head    += nreq;
 
+        /*
+         * Make sure doorbells don't leak out of RQ spinlock and reach
+         * the HCA out of order:
+         */
+        mmiowb();
+
         spin_unlock_irqrestore(&qp->rq.lock, flags);
         return err;
 }
@@ -2112,6 +2125,12 @@ out:
                               MTHCA_GET_DOORBELL_LOCK(&dev->doorbell_lock));
         }
 
+        /*
+         * Make sure doorbells don't leak out of SQ spinlock and reach
+         * the HCA out of order:
+         */
+        mmiowb();
+
         spin_unlock_irqrestore(&qp->sq.lock, flags);
         return err;
 }