On Fri, Dec 4, 2015 at 8:50 PM, David Miller <da...@davemloft.net> wrote: > From: Alexander Duyck <alexander.du...@gmail.com> > Date: Fri, 4 Dec 2015 14:44:00 -0800 > >> I actually tried to push the generic checksum idea for fm10k back >> during hardware development but ended up losing that battle. > > This chips already have a circuit calculating the 1's complement sum > over the data as is passed through the FIFO in the RTL, it's merely a > matter of putting the result it in the descriptor.
Actually it is a bit trickier than that. The problem is the L4 checksum doesn't include all of the L3 header in the pseudo header. So in order to add this feature and maintain the current feature you have to essentially compute two checksums. One with the pseudo header and one with the entire L3 header. In addition there are the fiddly little details like what to do about VLAN headers since I think they were included in the checksum if you leave them in the header, but you have to exclude them if they aren't. There is also the matter of if we include the L2 header or not. Basically there are number of odd corner cases and such where this really starts to become a pain. > Relatively speaking, the feature would be almost free. Right. I made similar arguments. The problem is the RTL they have works, and they don't want to change it unless they have to. Having a couple engineers write the RTL, then have some validation engineers test it, and some driver developer code it up costs money. In addition there is risk involved if some flaw slips through one of the validation efforts resulting in a silicon spin, or even worse if some flaw ends up being released. What it comes down to is that from the engineering side we likely won't be able to influence any change on the hardware design. We have to convince the sales and marketing folks for one of the vendors that implementing this feature would be beneficial to their bottom line if we want to see any actual change. Without that impetus there is no motivation on the vendors side to risk any of their capital trying to implement a feature that a few of us kernel engineers think would be a really good idea. - Alex -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
