On Fri, Aug 19, 2016 at 12:28 PM, David Miller <da...@davemloft.net> wrote: > From: Helmut Buchsbaum <helmut.buchsb...@gmail.com> > Date: Fri, 19 Aug 2016 15:04:57 +0200 > >> When working on upgrading the v3.x kernels of our embedded devices >> to more recent 4.x kernels we noticed some of our proprietary networking >> stuff is broken. Further investigations brought up an issue with small >> UDP packets (data payload <= 2), which contained wrong UDP header >> checksums. >> We tracked this down to commit 85ff3d87bf2ef1fadcde8553628c60f79806fdb4 >> net/macb: add TX checksum offload feature. It turns out that Zynq's GEM >> is obviously buggy regarding the UDP checksum calculation of such small >> UDP packets as long as the UDP checksum field is != 0 *BEFORE* the >> HW calulation. But since udp_send_skb() *ALWAYS* calculates the UDP header >> checksum (unless disabled via socket option), this is the usual case. >> Unfortunately it does not respect the net device feature setting which >> would leave UDP checksum untouched when checksum offloading is enabled. > > Then simply clear the checksum field in the driver, or fix > udp_send_skb() to do what you claim it is supposed to. > > That seems like a much more appropriate fix to me.
Fix the driver to do that. When offloading a UDP checksum the pseudo header checksum is written into the checksum field-- that's the interface that everyone else has been using without issue.
