Gianfar TCP checksumming broken in 2.6.35+

[David Miller]

From: "Matthew L. Creech" <mlcreech at gmail.com>
Date: Thu, 18 Nov 2010 14:31:46 -0500

> On Thu, Nov 18, 2010 at 12:06 PM, David Miller <davem at davemloft.net> wrote:
>>
>> Can someone please follow up Matthew to get this bug resolved?  It has
>> been sitting around for a long time.
>>
>> I suspect the gianfar driver, for these chip revisions, will need to
>> do a software checksum when the offset matches the criteria mentioned
>> in the errata above.
>>
> 
> I added a patch for this which fixes our affected systems; however, I
> don't know if this is a good way to perform checksum offloading, I
> just kind of dug around until I found a function that seemed like it
> worked.  :)  Patch against 2.6.36 is below for reference.

It looks fine except I would limit the software checksum to the
exact conditions listed in the errate.

Otherwise this is going to hurt performance and cpu utilization
quite a bit.