sh_eth: Mitigate lost statistics updates
The statistics registers have write-clear behaviour, which means we
will lose any increment between the read and write. Mitigate this by
only clearing when we read a non-zero value, so we will never falsely
report a total of zero. This also saves time as we only handle
error statistics here and they won't often be incremented.
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/renesas/sh_eth.c b/drivers/net/ethernet/renesas/sh_eth.c
index c92dd17..7fb244f 100644
--- a/drivers/net/ethernet/renesas/sh_eth.c
+++ b/drivers/net/ethernet/renesas/sh_eth.c
@@ -2417,6 +2417,22 @@
return NETDEV_TX_OK;
}
+/* The statistics registers have write-clear behaviour, which means we
+ * will lose any increment between the read and write. We mitigate
+ * this by only clearing when we read a non-zero value, so we will
+ * never falsely report a total of zero.
+ */
+static void
+sh_eth_update_stat(struct net_device *ndev, unsigned long *stat, int reg)
+{
+ u32 delta = sh_eth_read(ndev, reg);
+
+ if (delta) {
+ *stat += delta;
+ sh_eth_write(ndev, 0, reg);
+ }
+}
+
static struct net_device_stats *sh_eth_get_stats(struct net_device *ndev)
{
struct sh_eth_private *mdp = netdev_priv(ndev);
@@ -2427,21 +2443,18 @@
if (!mdp->is_opened)
return &ndev->stats;
- ndev->stats.tx_dropped += sh_eth_read(ndev, TROCR);
- sh_eth_write(ndev, 0, TROCR); /* (write clear) */
- ndev->stats.collisions += sh_eth_read(ndev, CDCR);
- sh_eth_write(ndev, 0, CDCR); /* (write clear) */
- ndev->stats.tx_carrier_errors += sh_eth_read(ndev, LCCR);
- sh_eth_write(ndev, 0, LCCR); /* (write clear) */
+ sh_eth_update_stat(ndev, &ndev->stats.tx_dropped, TROCR);
+ sh_eth_update_stat(ndev, &ndev->stats.collisions, CDCR);
+ sh_eth_update_stat(ndev, &ndev->stats.tx_carrier_errors, LCCR);
if (sh_eth_is_gether(mdp)) {
- ndev->stats.tx_carrier_errors += sh_eth_read(ndev, CERCR);
- sh_eth_write(ndev, 0, CERCR); /* (write clear) */
- ndev->stats.tx_carrier_errors += sh_eth_read(ndev, CEECR);
- sh_eth_write(ndev, 0, CEECR); /* (write clear) */
+ sh_eth_update_stat(ndev, &ndev->stats.tx_carrier_errors,
+ CERCR);
+ sh_eth_update_stat(ndev, &ndev->stats.tx_carrier_errors,
+ CEECR);
} else {
- ndev->stats.tx_carrier_errors += sh_eth_read(ndev, CNDCR);
- sh_eth_write(ndev, 0, CNDCR); /* (write clear) */
+ sh_eth_update_stat(ndev, &ndev->stats.tx_carrier_errors,
+ CNDCR);
}
return &ndev->stats;