be2net: fix erx->rx_drops_no_frags wrap around

The rx_drops_no_frags HW counter for RSS rings is 16bits in HW and can
wraparound often. Maintain a 32-bit accumulator in the driver to prevent
frequent wraparound.

Also, incorporated Eric's feedback to use ACCESS_ONCE() for the accumulator
write.

Signed-off-by: Sathya Perla <sathya.perla@emulex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/emulex/benet/be_main.c b/drivers/net/ethernet/emulex/benet/be_main.c
index 2375c0c..fb2eda0 100644 (file)
--- a/drivers/net/ethernet/emulex/benet/be_main.c
+++ b/drivers/net/ethernet/emulex/benet/be_main.c
@@ -378,6 +378,18 @@ static void populate_lancer_stats(struct be_adapter *adapter)
                                pport_stats->rx_drops_too_many_frags_lo;
 }
 
+static void accumulate_16bit_val(u32 *acc, u16 val)
+{
+#define lo(x)                  (x & 0xFFFF)
+#define hi(x)                  (x & 0xFFFF0000)
+       bool wrapped = val < lo(*acc);
+       u32 newacc = hi(*acc) + val;
+
+       if (wrapped)
+               newacc += 65536;
+       ACCESS_ONCE(*acc) = newacc;
+}
+
 void be_parse_stats(struct be_adapter *adapter)
 {
        struct be_erx_stats_v1 *erx = be_erx_stats_from_cmd(adapter);
@@ -394,9 +406,13 @@ void be_parse_stats(struct be_adapter *adapter)
        }
 
        /* as erx_v1 is longer than v0, ok to use v1 defn for v0 access */
-       for_all_rx_queues(adapter, rxo, i)
-               rx_stats(rxo)->rx_drops_no_frags =
-                       erx->rx_drops_no_fragments[rxo->q.id];
+       for_all_rx_queues(adapter, rxo, i) {
+               /* below erx HW counter can actually wrap around after
+                * 65535. Driver accumulates a 32-bit value
+                */
+               accumulate_16bit_val(&rx_stats(rxo)->rx_drops_no_frags,
+                               (u16)erx->rx_drops_no_fragments[rxo->q.id]);
+       }
 }
 
 static struct rtnl_link_stats64 *be_get_stats64(struct net_device *netdev,