From: Al Viro <viro@ftp.linux.org.uk>
To: netdev@vger.kernel.org
Subject: [RFC] skge csum problems
Date: Mon, 24 Dec 2007 09:43:52 +0000 [thread overview]
Message-ID: <20071224094352.GU8181@ftp.linux.org.uk> (raw)
Both variants of skge (drivers/net and drivers/net/sk98lin/ resp.)
have the same problem with rx checksums. They pick checksum from rx
descriptor and use it as-is. Normally that would be the right thing to
do. However, skge is told to byteswap descriptors on big-endian boxen.
Checksum is fixed-endian and we want it that way; IOW, what we end up
storing in skb->csum should be fixed-endian as well. Unless the card
is smart enough to byteswap everything in rx descriptor _except_ the
checksum, we have a trouble - we get a value converted to host-endian
by the general byteswap in descriptor and we must convert it to fixed-endian
ourselves.
FWIW, FreeBSD sk_if sidesteps that mess by not telling the card to
byteswap, so that's not too informative. Datasheet on
http://people.freebsd.org/~wpaul/SysKonnect/xmacii_datasheet_rev_c_9-29.pdf
is not clear on what's going on with checksum in byteswapping mode either...
Could somebody with that sucker on a card (all instances I have here are
on-board ones in little-endian boxen) test what's really going on for
big-endian hosts with either driver?
next reply other threads:[~2007-12-24 9:43 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-12-24 9:43 Al Viro [this message]
2007-12-24 13:15 ` [RFC] skge csum problems Andi Kleen
2007-12-24 18:39 ` Al Viro
2007-12-24 19:36 ` Stephen Hemminger
2007-12-24 19:45 ` Al Viro
2007-12-27 19:31 ` Stephen Hemminger
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