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smsc95xx: Fix tx checksum offload for small packets

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TX checksum offload does not work properly when transmitting
UDP packets with 0, 1 or 2 bytes of data.  This patch works
around the problem by calculating checksums for these packets
in the driver.

Signed-off-by: Steve Glendinning <steve.glendinning@smsc.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Steve Glendinning 2010-03-18 22:18:41 -07:00 committed by David S. Miller
parent 0ecad5a262
commit 11bc308837
1 changed files with 15 additions and 3 deletions
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18
drivers/net/usb/smsc95xx.c
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@ -1189,9 +1189,21 @@ static struct sk_buff *smsc95xx_tx_fixup(struct usbnet *dev,
}
if (csum) {
u32 csum_preamble = smsc95xx_calc_csum_preamble(skb);
skb_push(skb, 4);
memcpy(skb->data, &csum_preamble, 4);
if (skb->len <= 45) {
/* workaround - hardware tx checksum does not work
* properly with extremely small packets */
long csstart = skb->csum_start - skb_headroom(skb);
__wsum calc = csum_partial(skb->data + csstart,
skb->len - csstart, 0);
*((__sum16 *)(skb->data + csstart
+ skb->csum_offset)) = csum_fold(calc);
csum = false;
} else {
u32 csum_preamble = smsc95xx_calc_csum_preamble(skb);
skb_push(skb, 4);
memcpy(skb->data, &csum_preamble, 4);
}
}
skb_push(skb, 4);