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.
