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Date: Tue, 01 Nov 2016 10:50:01 +0000 From: Russell King <rmk+kernel@...linux.org.uk> To: Sebastian Hesselbarth <sebastian.hesselbarth@...il.com> Cc: netdev@...r.kernel.org Subject: [PATCH] net: mv643xx_eth: ensure coalesce settings survive read-modify-write The coalesce settings behave badly when changing just one value: ... # ethtool -c eth0 rx-usecs: 249 ... # ethtool -C eth0 tx-usecs 250 ... # ethtool -c eth0 rx-usecs: 248 This occurs due to rounding errors when calculating the microseconds value - the divisons round down. This causes (eg) the rx-usecs to decrease by one every time the tx-usecs value is set as per the above. Fix this by making the divison round-to-nearest. Signed-off-by: Russell King <rmk+kernel@...linux.org.uk> --- drivers/net/ethernet/marvell/mv643xx_eth.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/net/ethernet/marvell/mv643xx_eth.c b/drivers/net/ethernet/marvell/mv643xx_eth.c index 2a85202de6da..8a472cbfda09 100644 --- a/drivers/net/ethernet/marvell/mv643xx_eth.c +++ b/drivers/net/ethernet/marvell/mv643xx_eth.c @@ -1429,6 +1429,7 @@ static unsigned int get_rx_coal(struct mv643xx_eth_private *mp) temp = (val & 0x003fff00) >> 8; temp *= 64000000; + temp += mp->t_clk / 2; do_div(temp, mp->t_clk); return (unsigned int)temp; @@ -1465,6 +1466,7 @@ static unsigned int get_tx_coal(struct mv643xx_eth_private *mp) temp = (rdlp(mp, TX_FIFO_URGENT_THRESHOLD) & 0x3fff0) >> 4; temp *= 64000000; + temp += mp->t_clk / 2; do_div(temp, mp->t_clk); return (unsigned int)temp; -- 2.1.0
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