netdev - RE: [PATCH 3/3] net: fec: align IP header in hardware

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Date:   Mon, 26 Sep 2016 09:26:33 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Eric Nelson' <eric@...int.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "linux@....linux.org.uk" <linux@....linux.org.uk>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "fugang.duan@....com" <fugang.duan@....com>,
        "otavio@...ystems.com.br" <otavio@...ystems.com.br>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "troy.kisky@...ndarydevices.com" <troy.kisky@...ndarydevices.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "u.kleine-koenig@...gutronix.de" <u.kleine-koenig@...gutronix.de>
Subject: RE: [PATCH 3/3] net: fec: align IP header in hardware

From: Eric Nelson
> Sent: 24 September 2016 15:42
> The FEC receive accelerator (RACC) supports shifting the data payload of
> received packets by 16-bits, which aligns the payload (IP header) on a
> 4-byte boundary, which is, if not required, at least strongly suggested
> by the Linux networking layer.
...
> +		/* align IP header */
> +		val |= FEC_RACC_SHIFT16;

I can't help feeling that there needs to be corresponding
changes to increase the buffer size by 2 (maybe for large mtu)
and to discard two bytes from the frame length.

If probably ought to be predicated on NET_IP_ALIGN as well.

	David