[PATCH net-next] bnx2: use READ_ONCE() instead of barrier()

[Eric Dumazet]

From: Eric Dumazet <eduma...@google.com>

barrier() is a big hammer compared to READ_ONCE(),
and requires comments explaining what is protected.

READ_ONCE() is more precise and compiler should generate
better overall code.

Signed-off-by: Eric Dumazet <eduma...@google.com>
---
 drivers/net/ethernet/broadcom/bnx2.c |   17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/bnx2.c 
b/drivers/net/ethernet/broadcom/bnx2.c
index 
9960a9249dc0d0c8fb3494989e882a4c96e64970..d5d1026be4b70a320c48af7545a1891c74e19a47
 100644
--- a/drivers/net/ethernet/broadcom/bnx2.c
+++ b/drivers/net/ethernet/broadcom/bnx2.c
@@ -254,13 +254,10 @@ static inline u32 bnx2_tx_avail(struct bnx2 *bp, struct 
bnx2_tx_ring_info *txr)
 {
        u32 diff;
 
-       /* Tell compiler to fetch tx_prod and tx_cons from memory. */
-       barrier();
-
        /* The ring uses 256 indices for 255 entries, one of them
         * needs to be skipped.
         */
-       diff = txr->tx_prod - txr->tx_cons;
+       diff = READ_ONCE(txr->tx_prod) - READ_ONCE(txr->tx_cons);
        if (unlikely(diff >= BNX2_TX_DESC_CNT)) {
                diff &= 0xffff;
                if (diff == BNX2_TX_DESC_CNT)
@@ -2839,10 +2836,8 @@ bnx2_get_hw_tx_cons(struct bnx2_napi *bnapi)
 {
        u16 cons;
 
-       /* Tell compiler that status block fields can change. */
-       barrier();
-       cons = *bnapi->hw_tx_cons_ptr;
-       barrier();
+       cons = READ_ONCE(*bnapi->hw_tx_cons_ptr);
+
        if (unlikely((cons & BNX2_MAX_TX_DESC_CNT) == BNX2_MAX_TX_DESC_CNT))
                cons++;
        return cons;
@@ -3141,10 +3136,8 @@ bnx2_get_hw_rx_cons(struct bnx2_napi *bnapi)
 {
        u16 cons;
 
-       /* Tell compiler that status block fields can change. */
-       barrier();
-       cons = *bnapi->hw_rx_cons_ptr;
-       barrier();
+       cons = READ_ONCE(*bnapi->hw_rx_cons_ptr);
+
        if (unlikely((cons & BNX2_MAX_RX_DESC_CNT) == BNX2_MAX_RX_DESC_CNT))
                cons++;
        return cons;