> From: Eric Dumazet [mailto:eric.duma...@gmail.com] > Sent: 15 listopada 2016 14:12 > To: Rafal Ozieblo > Cc: David Miller; nicolas.fe...@atmel.com; net...@vger.kernel.org; > linux-kernel@vger.kernel.org > Subject: Re: [PATCH net-next v5] cadence: Add LSO support. > > On Tue, 2016-11-15 at 07:07 +0000, Rafal Ozieblo wrote: > > > > > If UFO is in use it should not silently disable UDP checksums. > > > > > > > > > > If you cannot support UFO with proper checksumming, then you cannot > > > > > enable support for that feature. > > > > > > > > According Cadence Gigabit Ethernet MAC documentation: > > > > > > > > "Hardware will not calculate the UDP checksum or modify the UDP > > > > checksum field. Therefore software must set a value of zero in the > > > > checksum field in the UDP header (in the first payload buffer) to > > > > indicate to the receiver that the UDP datagram does not include a > > > > checksum." > > > > > > > > It is hardware requirement. > > > > > > I do not doubt that it is a hardware restriction. > > > > > > But I am saying that you cannot enable this feature under Linux if this > > > is how it operates on your hardware. > > > > Would it be good to enable UFO conditionally with some internal define? Ex.: > > > > +#ifdef MACB_ENABLE_UFO > > +#define MACB_NETIF_LSO (NETIF_F_TSO | NETIF_F_UFO) > > +#else > > +#define MACB_NETIF_LSO (NETIF_F_TSO) > > +#endif > > > > I could add precise comment here that ufo is possible only without checksum. > > > > Or maybe I could enable it from module_params or device-tree (like: > > drivers/net/ethernet/neterion/s2io.c). > > No you can not do that. > > 1) That would violate UDP specs. > 2) Module params are no longer accepted. > 3) Comments in a driver source code would only help the driver maintainer, > not users to make their mind. > > Only way would be to propagate the intent of the sender. > > Only the sender application can decide to generate UDP checksums or not. > > Your driver ndo_features_check() could then force software segmentation > fallback if the user did not asked to disable UDP checksums, and packet is > UFO. > > (look for UDP_NO_CHECK6_TX, and SO_NO_CHECK ) > > Problem is complex, because the skb has no marker, only the socket has. > > And socket state could change between packets, and packets can stay in an > intermediate qdisc before hitting device driver. So looking at > skb->sk from your ndo_features_check() would be racy. > > What use case would you have precisely ?
I have talked with hardware team who designed and created gem IP. The conclusion is that there is no need to zeroed checksum for UFO. I have tested UFO without zeroing UDP checksum on cadence gem. It works fine. I'll deeply investigate and test UFO again. I'll send version 6 of LSO PATCH either with UFO without zeroing or without UFO at all.
