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

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Date:   Sun, 16 Dec 2018 21:59:15 +0100
From:   Simon Horman <horms@...ge.net.au>
To:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
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

On Mon, Dec 10, 2018 at 07:56:14PM +0300, Sergei Shtylyov wrote:
> 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)?

I was hoping that others would test the patch on the same or other boards.
That is all.

> 
> > 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.

It seems that David likes the #define, lets keep it.