netdev - Re: [PATCH net-next] net: mscc: allow extracting the FCS into the skb

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Date:   Mon, 1 Oct 2018 09:35:45 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Antoine Tenart <antoine.tenart@...tlin.com>, davem@...emloft.net
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        thomas.petazzoni@...tlin.com, alexandre.belloni@...tlin.com,
        quentin.schulz@...tlin.com, allan.nielsen@...rochip.com
Subject: Re: [PATCH net-next] net: mscc: allow extracting the FCS into the skb

On 10/01/2018 02:57 AM, Antoine Tenart wrote:
> This patch adds support for the NETIF_F_RXFCS feature in the Mscc
> Ethernet driver. This feature is disabled by default and allow an user
> to request the driver not to drop the FCS and to extract it into the skb
> for debugging purposes.
> 
> Signed-off-by: Antoine Tenart <antoine.tenart@...tlin.com>
> ---
>  drivers/net/ethernet/mscc/ocelot.c       | 2 +-
>  drivers/net/ethernet/mscc/ocelot_board.c | 7 ++++++-
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mscc/ocelot.c b/drivers/net/ethernet/mscc/ocelot.c
> index 1a4f2bb48ead..eb5119e7e60b 100644
> --- a/drivers/net/ethernet/mscc/ocelot.c
> +++ b/drivers/net/ethernet/mscc/ocelot.c
> @@ -1606,7 +1606,7 @@ int ocelot_probe_port(struct ocelot *ocelot, u8 port,
>  	dev->ethtool_ops = &ocelot_ethtool_ops;
>  	dev->switchdev_ops = &ocelot_port_switchdev_ops;
>  
> -	dev->hw_features |= NETIF_F_HW_VLAN_CTAG_FILTER;
> +	dev->hw_features |= NETIF_F_HW_VLAN_CTAG_FILTER | NETIF_F_RXFCS;
>  	dev->features |= NETIF_F_HW_VLAN_CTAG_FILTER;
>  
>  	memcpy(dev->dev_addr, ocelot->base_mac, ETH_ALEN);
> diff --git a/drivers/net/ethernet/mscc/ocelot_board.c b/drivers/net/ethernet/mscc/ocelot_board.c
> index 3cdf63e35b53..245452a0f244 100644
> --- a/drivers/net/ethernet/mscc/ocelot_board.c
> +++ b/drivers/net/ethernet/mscc/ocelot_board.c
> @@ -126,11 +126,16 @@ static irqreturn_t ocelot_xtr_irq_handler(int irq, void *arg)
>  			len += sz;
>  		} while (len < buf_len);
>  
> -		/* Read the FCS and discard it */
> +		/* Read the FCS */
>  		sz = ocelot_rx_frame_word(ocelot, grp, false, &val);
>  		/* Update the statistics if part of the FCS was read before */
>  		len -= ETH_FCS_LEN - sz;
>  
Don't this needs to be len -= sz;


> +		if (unlikely(dev->features & NETIF_F_RXFCS)) {
> +			buf = (u32 *)skb_put(skb, ETH_FCS_LEN);
> +			*buf = val;

and here len -= ETH_FCS_LEN

since "len" is later used for accounting how many bytes have been
received by the network device?

I am bit confused by the use of "buf", but presumably if NETIF_F_RXCFS
is turned on, the FCS needs to be part of the buffer passed to the
network stack, so adjusting len accordingly is required anyway.
-- 
Florian