netdev - Re: [PATCH v2] gianfar: fix size of scatter-gathered frames

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Message-Id: <20160823.164913.1405890361099687642.davem@davemloft.net>
Date:   Tue, 23 Aug 2016 16:49:13 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     zefir.kurtisi@...atec.com
Cc:     netdev@...r.kernel.org, claudiu.manoil@...escale.com,
        andrew@...n.ch
Subject: Re: [PATCH v2] gianfar: fix size of scatter-gathered frames

From: Zefir Kurtisi <zefir.kurtisi@...atec.com>
Date: Mon, 22 Aug 2016 15:58:12 +0200

> The current scatter-gather logic in gianfar is flawed, since
> it does not consider the eTSEC's RxBD 'Data Length' field is
> context depening: for the last fragment it contains the full
> frame size, while fragments contain the fragment size, which
> equals the value written to register MRBLR.
> 
> This causes data corruption as soon as the hardware starts
> to fragment receiving frames. As a result, the size of
> fragmented frames is increased by
> (nr_frags - 1) * MRBLR
> 
> We first noticed this issue working with DSA, where an ICMP
> request sized 1472 bytes causes the scatter-gather logic to
> kick in. The full Ethernet frame (1518) gets increased by
> DSA (4), GMAC_FCB_LEN (8), and FSL_GIANFAR_DEV_HAS_TIMER
> (priv->padding=8) to a total of 1538 octets, which is
> fragmented by the hardware and reconstructed by the driver
> to a 3074 octet frame.
> 
> This patch fixes the problem by adjusting the size of
> the last fragment.
> 
> It was tested by setting MRBLR to different multiples of
> 64, proving correct scatter-gather operation on frames
> with up to 9000 octets in size.
> 
> Signed-off-by: Zefir Kurtisi <zefir.kurtisi@...atec.com>

Applied.