From 11bc3088373e913f165a8652601c6f8b8dc4aea2 Mon Sep 17 00:00:00 2001 From: Steve Glendinning Date: Thu, 18 Mar 2010 22:18:41 -0700 Subject: [PATCH] smsc95xx: Fix tx checksum offload for small packets 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 Signed-off-by: David S. Miller --- drivers/net/usb/smsc95xx.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/drivers/net/usb/smsc95xx.c b/drivers/net/usb/smsc95xx.c index d222d7e25273..73f9a31cf94d 100644 --- a/drivers/net/usb/smsc95xx.c +++ b/drivers/net/usb/smsc95xx.c @@ -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); -- 2.20.1