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Commit 4398f9c8 authored by Ben Hutchings's avatar Ben Hutchings Committed by David S. Miller
Browse files

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: default avatarBen Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent e5fd13f4

drivers/net/ethernet/renesas/sh_eth.c

+25 −12
Original line number Diff line number Diff line
@@ -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;