netdev - Re: [patch net / RFC] net: fec: increase frame size limitation to actually available buffer

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Date:   Wed, 30 Nov 2016 17:05:09 +0100
From:   Zefir Kurtisi <zefir.kurtisi@...atec.com>
To:     Nikita Yushchenko <nikita.yoush@...entembedded.com>,
        "David S. Miller" <davem@...emloft.net>,
        Fugang Duan <fugang.duan@....com>,
        Troy Kisky <troy.kisky@...ndarydevices.com>,
        Andrew Lunn <andrew@...n.ch>, Eric Nelson <eric@...int.com>,
        Philippe Reynes <tremyfr@...il.com>,
        Johannes Berg <johannes@...solutions.net>,
        netdev@...r.kernel.org
Cc:     Chris Healy <cphealy@...il.com>,
        Fabio Estevam <fabio.estevam@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [patch net / RFC] net: fec: increase frame size limitation to
 actually available buffer

On 11/29/2016 07:35 PM, Nikita Yushchenko wrote:
> Fec driver uses Rx buffers of 2k, but programs hardware to limit
> incoming frames to 1522 bytes. This raises issues when FEC device
> is used with DSA (since DSA tag can make frame larger), and also
> disallows manual sending and receiving larger frames.
> 
> This patch removes the limitation, allowing Rx size up to entire buffer.
> At the same time possible Tx size is increased as well, because hardware
> uses the same register field to limit Rx and Tx.
> 
> Signed-off-by: Nikita Yushchenko <nikita.yoush@...entembedded.com>
> ---

I recently did similar changes to the freescale/gianfar to prevent fragmentation
of (E)DSA frames [1].

With the fragmentation kicking in, I noticed a bug in the scatter-gather logic
which caused the frame-size of fragmented frames to be reported wrong [2]. Not
sure if the fec driver has SG capabilities and if this issue also applies, you
might want to double-check.


Cheers,
Zefir


[1] http://marc.info/?l=linux-netdev&m=147187438313519&w=2
[2] http://marc.info/?l=linux-netdev&m=147187430213484&w=2