netdev - RE: [PATCH net-next v5] cadence: Add LSO support.

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Date:   Tue, 15 Nov 2016 07:07:14 +0000
From:   Rafal Ozieblo <rafalo@...ence.com>
To:     David Miller <davem@...emloft.net>
CC:     "nicolas.ferre@...el.com" <nicolas.ferre@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH net-next v5] cadence: Add LSO support.

> > > 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).