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

From: David Miller [mailto:davem@davemloft.net] 
Sent: 10 listopada 2016 18:01
To: Rafal Ozieblo
Cc: nicolas.ferre@atmel.com; netdev@vger.kernel.org; linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next v5]] cadence: Add LSO support.

From: Rafal Ozieblo <redacted>
Date: Wed, 9 Nov 2016 13:41:02 +0000

First, please remove the spurious closing bracket in your Subject line in future submittions.

quoted

+	if (is_udp) /* is_udp is only set when (is_lso) is checked */
+		/* zero UDP checksum, not calculated by h/w for UFO */
+		udp_hdr(skb)->check = 0;

This is really not ok.

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.