netdev - Re: [PATCH v2] gianfar: prevent fragmentation in DSA environments

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Date:   Tue, 23 Aug 2016 16:49:20 -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: prevent fragmentation in DSA environments

From: Zefir Kurtisi <zefir.kurtisi@...atec.com>
Date: Mon, 22 Aug 2016 15:56:38 +0200

> The eTSEC register MRBLR defines the maximum space in
> the RX buffers and is set to 1536 by gianfar. This
> reasonably covers the common use case where the MTU
> is kept at default 1500. In that case, the largest
> Ethernet frame size of 1518 plus an optional
> GMAC_FCB_LEN of 8, and an additional padding of 8
> to handle FSL_GIANFAR_DEV_HAS_TIMER totals to 1534
> and nicely fit within the chosen MRBLR.
> 
> Alas, if the eTSEC is attached to a DSA enabled switch,
> the (E)DSA header extension (4 or 8 bytes) causes every
> maximum sized frame to be fragmented by the hardware.
> 
> This patch increases the maximum RX buffer size by 8
> and rounds up to the next multiple of 64, which the
> hardware's defines as RX buffer granularity.
> 
> Signed-off-by: Zefir Kurtisi <zefir.kurtisi@...atec.com>

Applied.