From 4398f9c817028b3b654923b3b614ea174cbc2c67 Mon Sep 17 00:00:00 2001 From: Ben Hutchings Date: Thu, 26 Feb 2015 20:35:05 +0000 Subject: [PATCH] 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 Signed-off-by: David S. Miller --- drivers/net/ethernet/renesas/sh_eth.c | 37 ++++++++++++++++++--------- 1 file changed, 25 insertions(+), 12 deletions(-) diff --git a/drivers/net/ethernet/renesas/sh_eth.c b/drivers/net/ethernet/renesas/sh_eth.c index c92dd173b994..7fb244f565b2 100644 --- a/drivers/net/ethernet/renesas/sh_eth.c +++ b/drivers/net/ethernet/renesas/sh_eth.c @@ -2417,6 +2417,22 @@ static int sh_eth_start_xmit(struct sk_buff *skb, struct net_device *ndev) 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 @@ static struct net_device_stats *sh_eth_get_stats(struct net_device *ndev) 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; -- 2.20.1