IB/mthca: Simplify use of size0 in work request posting

Current code sets size0 to 0 at the start of work request posting
functions and then handles size0 == 0 specially within the loop over
work requests.  Change this so size0 is set along with f0 the first
time through the loop (when nreq == 0).  This makes the code easier to
understand by making it clearer that f0 and size0 are always
initialized if nreq != 0 without having to know that size0 == 0
implies nreq == 0.

Also annotate size0 with uninitialized_var() so that this doesn't
introduce a new compiler warning.

Signed-off-by: Roland Dreier <rolandd@cisco.com>

diff --git a/drivers/infiniband/hw/mthca/mthca_qp.c b/drivers/infiniband/hw/mthca/mthca_qp.c
index b5bd704..df01b20 100644 (file)
--- a/drivers/infiniband/hw/mthca/mthca_qp.c
+++ b/drivers/infiniband/hw/mthca/mthca_qp.c
@@ -1629,13 +1629,14 @@ int mthca_tavor_post_send(struct ib_qp *ibqp, struct ib_send_wr *wr,
        int nreq;
        int i;
        int size;
-       int size0 = 0;
        /*
-        * f0 is only used if nreq != 0, and f0 will be initialized
-        * the first time through the main loop, since size0 == 0 the
-        * first time through.  So nreq cannot become non-zero without
-        * initializing f0, and f0 is in fact never used uninitialized.
+        * f0 and size0 are only used if nreq != 0, and they will
+        * always be initialized the first time through the main loop
+        * before nreq is incremented.  So nreq cannot become non-zero
+        * without initializing f0 and size0, and they are in fact
+        * never used uninitialized.
         */
+       int uninitialized_var(size0);
        u32 uninitialized_var(f0);
        int ind;
        u8 op0 = 0;
@@ -1780,11 +1781,11 @@ int mthca_tavor_post_send(struct ib_qp *ibqp, struct ib_send_wr *wr,
                                    mthca_opcode[wr->opcode]);
                wmb();
                ((struct mthca_next_seg *) prev_wqe)->ee_nds =
-                       cpu_to_be32((size0 ? 0 : MTHCA_NEXT_DBD) | size |
+                       cpu_to_be32((nreq ? 0 : MTHCA_NEXT_DBD) | size |
                                    ((wr->send_flags & IB_SEND_FENCE) ?
                                    MTHCA_NEXT_FENCE : 0));
 
-               if (!size0) {
+               if (!nreq) {
                        size0 = size;
                        op0   = mthca_opcode[wr->opcode];
                        f0    = wr->send_flags & IB_SEND_FENCE ?
@@ -1834,7 +1835,14 @@ int mthca_tavor_post_receive(struct ib_qp *ibqp, struct ib_recv_wr *wr,
        int nreq;
        int i;
        int size;
-       int size0 = 0;
+       /*
+        * size0 is only used if nreq != 0, and it will always be
+        * initialized the first time through the main loop before
+        * nreq is incremented.  So nreq cannot become non-zero
+        * without initializing size0, and it is in fact never used
+        * uninitialized.
+        */
+       int uninitialized_var(size0);
        int ind;
        void *wqe;
        void *prev_wqe;
@@ -1888,7 +1896,7 @@ int mthca_tavor_post_receive(struct ib_qp *ibqp, struct ib_recv_wr *wr,
                ((struct mthca_next_seg *) prev_wqe)->ee_nds =
                        cpu_to_be32(MTHCA_NEXT_DBD | size);
 
-               if (!size0)
+               if (!nreq)
                        size0 = size;
 
                ++ind;
@@ -1910,7 +1918,6 @@ int mthca_tavor_post_receive(struct ib_qp *ibqp, struct ib_recv_wr *wr,
 
                        qp->rq.next_ind = ind;
                        qp->rq.head += MTHCA_TAVOR_MAX_WQES_PER_RECV_DB;
-                       size0 = 0;
                }
        }
 
@@ -1952,13 +1959,14 @@ int mthca_arbel_post_send(struct ib_qp *ibqp, struct ib_send_wr *wr,
        int nreq;
        int i;
        int size;
-       int size0 = 0;
        /*
-        * f0 is only used if nreq != 0, and f0 will be initialized
-        * the first time through the main loop, since size0 == 0 the
-        * first time through.  So nreq cannot become non-zero without
-        * initializing f0, and f0 is in fact never used uninitialized.
+        * f0 and size0 are only used if nreq != 0, and they will
+        * always be initialized the first time through the main loop
+        * before nreq is incremented.  So nreq cannot become non-zero
+        * without initializing f0 and size0, and they are in fact
+        * never used uninitialized.
         */
+       int uninitialized_var(size0);
        u32 uninitialized_var(f0);
        int ind;
        u8 op0 = 0;
@@ -1979,7 +1987,6 @@ int mthca_arbel_post_send(struct ib_qp *ibqp, struct ib_send_wr *wr,
                        doorbell[1] = cpu_to_be32((qp->qpn << 8) | size0);
 
                        qp->sq.head += MTHCA_ARBEL_MAX_WQES_PER_SEND_DB;
-                       size0 = 0;
 
                        /*
                         * Make sure that descriptors are written before
@@ -2133,7 +2140,7 @@ int mthca_arbel_post_send(struct ib_qp *ibqp, struct ib_send_wr *wr,
                                    ((wr->send_flags & IB_SEND_FENCE) ?
                                     MTHCA_NEXT_FENCE : 0));
 
-               if (!size0) {
+               if (!nreq) {
                        size0 = size;
                        op0   = mthca_opcode[wr->opcode];
                        f0    = wr->send_flags & IB_SEND_FENCE ?