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

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Date:   Mon, 14 Nov 2016 09:32:34 +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.

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

From: Rafal Ozieblo <rafalo@...ence.com>
Date: Wed, 9 Nov 2016 13:41:02 +0000

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