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

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Date:   Mon, 10 Dec 2018 19:56:14 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Simon Horman <horms+renesas@...ge.net.au>
Cc:     Magnus Damm <magnus.damm@...il.com>, netdev@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH/RFT net] ravb: expand rx descriptor data to accommodate hw
 checksum

Hello!

On 12/10/2018 11:59 AM, Simon Horman wrote:

> From: Simon Horman <horms@...ge.net.au>
> 
> 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. It also introduces
> RAVB_CSUM_LEN to make things a little clearer than "2" sprinkled lightly
> over the driver.

   I think a comment would work better in this case.

> Tested on R-Car E3 (r8a77990) ES1.0 based Ebisu-4D board

   You need more testing (RFT specified in the subject)?

> Fixes: 4d86d3818627 ("ravb: RX checksum offload")
> Signed-off-by: Simon Horman <horms+renesas@...ge.net.au>
> ---
>  drivers/net/ethernet/renesas/ravb_main.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
>  I have marked this patch as RTF as I would like it to see further testing
>  before being applied.
> 
> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> index defed0d0c51d..f7f130cf61e4 100644
> --- a/drivers/net/ethernet/renesas/ravb_main.c
> +++ b/drivers/net/ethernet/renesas/ravb_main.c
> @@ -40,6 +40,8 @@
>  		 NETIF_MSG_RX_ERR | \
>  		 NETIF_MSG_TX_ERR)
>  
> +#define RAVB_CSUM_LEN 2

   What's EtherAVB specific there, why RAVB prefix?

[...]
> @@ -350,7 +352,7 @@ static int ravb_ring_init(struct net_device *ndev, int q)
>  	int i;
>  
>  	priv->rx_buf_sz = (ndev->mtu <= 1492 ? PKT_BUF_SZ : ndev->mtu) +
> -		ETH_HLEN + VLAN_HLEN;
> +		ETH_HLEN + VLAN_HLEN + RAVB_CSUM_LEN;

   This is a fix per se. Let's add the #define (if we really need it) in
another patch.

[...]

MBR, Sergei