netdev - RE: [PATCH v5 07/14] net: pch_gbe: Fix handling of TX padding

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Date:   Mon, 19 Feb 2018 14:01:25 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Paul Burton' <paul.burton@...s.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     Hassan Naveed <hassan.naveed@...s.com>,
        Matt Redfearn <matt.redfearn@...s.com>,
        "David S . Miller" <davem@...emloft.net>,
        "linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org>
Subject: RE: [PATCH v5 07/14] net: pch_gbe: Fix handling of TX padding

From: Paul Burton
> Sent: 17 February 2018 20:11
> 
> The ethernet controller found in the Intel EG20T Platform Controller
> Hub requires that we place 2 bytes of padding between the ethernet
> header & the packet payload. Our pch_gbe driver handles this by copying
> packets to be transmitted to a temporary struct skb with the padding
> bytes inserted
...

Uggg WFT is the driver doing that for?

I'd guess that the two byte pad is there so that a 4 byte aligned
frame is still 4 byte aligned when the 14 byte ethernet header is added.
So instead of copying the entire frame the MAC header should be built
(or rebuilt?) two bytes further from the actual data.

	David