CHECKSUM_HW not behaving as expected

[Abraham vd Merwe <abraham@2d3d.co.za>]

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Hi!

In Rubini's "Linux Device Drivers 2nd edition" he states in his networking
chapter that skb->ip_summed = CHECKSUM_HW means that the hardware already
performed a checksum and that the upper layers therefore don't need to do it
(He also states that CHECKSUM_NONE (default) means that it still needs to be
verified).

I'm currently writing a network driver for 2.4.17 and the chip automatically
performs checksums and you can tell it to exclude the CRC from the packet or
not before making it available for the host. Now, if I configure it to
exclude the CRC and use skb->ip_summed = CHECKSUM_HW I get:

root@frodo:/# ./ldm
Using /cs8900.o
CS8900A driver for 2d3D, SA-1110 Development Board.
eth0: CS8900A rev D detected
configuring network:.
root@frodo:/# icmp v4 hw csum failure
icmp v4 hw csum failure
icmp v4 hw csum failure
icmp v4 hw csum failure
icmp v4 hw csum failure
icmp v4 hw csum failure
icmp v4 hw csum failure
icmp v4 hw csum failure
icmp v4 hw csum failure
icmp v4 hw csum failure
icmp v4 hw csum failure
icmp v4 hw csum failure
NET: 3 messages suppressed.
icmp v4 hw csum failure

root@frodo:/#
------------< snip <------< snip <------< snip <------------

If I used CHECKSUM_NONE, it works fine which obviously means that the CRC is
not computed in software.

Is that a bug in the kernel or does Alessandro have it wrong?

-- 

Regards
 Abraham

There is one difference between a tax collector and a taxidermist --
the taxidermist leaves the hide.
		-- Mortimer Caplan

__________________________________________________________
 Abraham vd Merwe - 2d3D, Inc.

 Device Driver Development, Outsourcing, Embedded Systems

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