netdev - Re: [PATCH v2 net] ravb: expand rx descriptor data to accommodate hw checksum

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Message-Id: <20190123.092557.657889811053553529.davem@davemloft.net>
Date:   Wed, 23 Jan 2019 09:25:57 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     horms+renesas@...ge.net.au
Cc:     sergei.shtylyov@...entembedded.com, magnus.damm@...il.com,
        netdev@...r.kernel.org, linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH v2 net] ravb: expand rx descriptor data to accommodate
 hw checksum

From: Simon Horman <horms+renesas@...ge.net.au>
Date: Wed, 23 Jan 2019 12:14:52 +0100

> EtherAVB may provide a checksum of packet data appended to packet data. In
> order to allow this checksum to be received by the host descriptor data
> needs to be enlarged by 2 bytes to accommodate the checksum.
> 
> In the case of MTU-sized packets without a VLAN tag the
> checksum were already accommodated by virtue of the space reserved for the
> VLAN tag. However, a packet of MTU-size with a  VLAN tag consumed all
> packet data space provided by a descriptor leaving no space for the
> trailing checksum.
> 
> This was not detected by the driver which incorrectly used the last two
> bytes of packet data as the checksum and truncate the packet by two bytes.
> This resulted all such packets being dropped.
> 
> A work around is to disable RX checksum offload
>  # ethtool -K eth0 rx off
> 
> This patch resolves this problem by increasing the size available for
> packet data in RX descriptors by two bytes.
> 
> Tested on R-Car E3 (r8a77990) ES1.0 based Ebisu-4D board
> 
> v2
> * Use sizeof(__sum16) directly rather than adding a driver-local
>   #define for the size of the checksum provided by the hw (2 bytes).
> 
> Fixes: 4d86d3818627 ("ravb: RX checksum offload")
> Signed-off-by: Simon Horman <horms+renesas@...ge.net.au>

Applied and queued up for -stable.