Re: [PATCH 2.6] POWER5 Virtual Ethernet Checkum offload

[Jeff Garzik <jgarzik@pobox.com>]

Santiago Leon wrote:
> Andrew,
> 
> The following patch adds checksum offloading for the POWER5 Virtual 
> Ethernet driver.  In the case where the OS in the partitions 
> communicating support this feature (i.e. both partition have this patch 
> applied), no checksum will be created because the link is reliable. 
> However, in the case where one of the OS in a partition does support 
> this feature and the other doesn't (i.e. linux with patch applied 
> talking to AIX), then the hypervisor will generate the checksum.
> 
> Some levels of firmware will not support this feature but the code will 
> figure it out and not enable it.
> 
> Applies against the latest mainline and -mm trees. Please apply.

First, please always CC net driver patches to me and netdev@oss.sgi.com.

Second, this patch is incorrect.  Read the top of include/linux/skbuff.h 
for the various levels of checksum offloading, and how to use them.

Specifically,

a) you should not be using CHECKSUM_HW unless your hardware provides a 
valid csum (ipv4 or ipv6) that you store in skb->csum.

b) you should not be using NETIF_F_HW_CSUM for reasons similar to (a): 
your hardware must be able to csum the packet whether its ipv4 or ipv6 
or whatever, given the information in the skb.

c) use of NETIF_F_xxx_CSUM is pointless without NETIF_F_SG and code in 
the transmit path to handle page-based fragments (a scatter-gather list).

	Jeff