sfc: Fix interface statistics running backward

Some interface statistics are computed in such a way that they can
sometimes decrease (and even underflow).  Since the computed value
will never be greater than the true value, we fix this by only storing
the computed value when it increases.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/drivers/net/ethernet/sfc/siena.c b/drivers/net/ethernet/sfc/siena.c
index 2354886293db..6bafd216e55e 100644
--- a/drivers/net/ethernet/sfc/siena.c
+++ b/drivers/net/ethernet/sfc/siena.c
@@ -458,8 +458,8 @@ static int siena_try_update_nic_stats(struct efx_nic *efx)
 
         MAC_STAT(tx_bytes, TX_BYTES);
         MAC_STAT(tx_bad_bytes, TX_BAD_BYTES);
-        mac_stats->tx_good_bytes = (mac_stats->tx_bytes -
-                                    mac_stats->tx_bad_bytes);
+        efx_update_diff_stat(&mac_stats->tx_good_bytes,
+                             mac_stats->tx_bytes - mac_stats->tx_bad_bytes);
         MAC_STAT(tx_packets, TX_PKTS);
         MAC_STAT(tx_bad, TX_BAD_FCS_PKTS);
         MAC_STAT(tx_pause, TX_PAUSE_PKTS);
@@ -492,8 +492,8 @@ static int siena_try_update_nic_stats(struct efx_nic *efx)
         MAC_STAT(tx_ip_src_error, TX_IP_SRC_ERR_PKTS);
         MAC_STAT(rx_bytes, RX_BYTES);
         MAC_STAT(rx_bad_bytes, RX_BAD_BYTES);
-        mac_stats->rx_good_bytes = (mac_stats->rx_bytes -
-                                    mac_stats->rx_bad_bytes);
+        efx_update_diff_stat(&mac_stats->rx_good_bytes,
+                             mac_stats->rx_bytes - mac_stats->rx_bad_bytes);
         MAC_STAT(rx_packets, RX_PKTS);
         MAC_STAT(rx_good, RX_GOOD_PKTS);
         MAC_STAT(rx_bad, RX_BAD_FCS_PKTS);