[PATCH net-next v2 1/2] ibmvnic: rework to ensure SCRQ entry reads are properly ordered

[Lijun Pan]

Move the dma_rmb() between pending_scrq() and ibmvnic_next_scrq()
into the end of pending_scrq() to save the duplicated code since
this dma_rmb will be used 3 times.

Signed-off-by: Lijun Pan <l...@linux.ibm.com>
Acked-by: Thomas Falcon <tlfal...@linux.ibm.com>
---
 drivers/net/ethernet/ibm/ibmvnic.c | 30 +++++++++++-------------------
 1 file changed, 11 insertions(+), 19 deletions(-)

diff --git a/drivers/net/ethernet/ibm/ibmvnic.c 
b/drivers/net/ethernet/ibm/ibmvnic.c
index a40af510018a..331ebca2f57a 100644
--- a/drivers/net/ethernet/ibm/ibmvnic.c
+++ b/drivers/net/ethernet/ibm/ibmvnic.c
@@ -2444,12 +2444,6 @@ static int ibmvnic_poll(struct napi_struct *napi, int 
budget)
 
                if (!pending_scrq(adapter, rx_scrq))
                        break;
-               /* The queue entry at the current index is peeked at above
-                * to determine that there is a valid descriptor awaiting
-                * processing. We want to be sure that the current slot
-                * holds a valid descriptor before reading its contents.
-                */
-               dma_rmb();
                next = ibmvnic_next_scrq(adapter, rx_scrq);
                rx_buff =
                    (struct ibmvnic_rx_buff *)be64_to_cpu(next->
@@ -3189,13 +3183,6 @@ static int ibmvnic_complete_tx(struct ibmvnic_adapter 
*adapter,
                int total_bytes = 0;
                int num_packets = 0;
 
-               /* The queue entry at the current index is peeked at above
-                * to determine that there is a valid descriptor awaiting
-                * processing. We want to be sure that the current slot
-                * holds a valid descriptor before reading its contents.
-                */
-               dma_rmb();
-
                next = ibmvnic_next_scrq(adapter, scrq);
                for (i = 0; i < next->tx_comp.num_comps; i++) {
                        if (next->tx_comp.rcs[i])
@@ -3569,11 +3556,16 @@ static int pending_scrq(struct ibmvnic_adapter *adapter,
                        struct ibmvnic_sub_crq_queue *scrq)
 {
        union sub_crq *entry = &scrq->msgs[scrq->cur];
+       int rc;
 
-       if (entry->generic.first & IBMVNIC_CRQ_CMD_RSP)
-               return 1;
-       else
-               return 0;
+       rc = !!(entry->generic.first & IBMVNIC_CRQ_CMD_RSP);
+
+       /* Ensure that the SCRQ valid flag is loaded prior to loading the
+        * contents of the SCRQ descriptor
+        */
+       dma_rmb();
+
+       return rc;
 }
 
 static union sub_crq *ibmvnic_next_scrq(struct ibmvnic_adapter *adapter,
@@ -3592,8 +3584,8 @@ static union sub_crq *ibmvnic_next_scrq(struct 
ibmvnic_adapter *adapter,
        }
        spin_unlock_irqrestore(&scrq->lock, flags);
 
-       /* Ensure that the entire buffer descriptor has been
-        * loaded before reading its contents
+       /* Ensure that the SCRQ valid flag is loaded prior to loading the
+        * contents of the SCRQ descriptor
         */
        dma_rmb();
 
-- 
2.23.0