[PATCH] net: mv643xx_eth: ensure coalesce settings survive read-modify-write

[Russell King]

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+ker...@armlinux.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