netdev - Re: [RFC net-next 6/9] net: dsa: Forward offloading

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Date:   Tue, 27 Apr 2021 13:17:47 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Tobias Waldekranz <tobias@...dekranz.com>
Cc:     davem@...emloft.net, kuba@...nel.org, andrew@...n.ch,
        vivien.didelot@...il.com, f.fainelli@...il.com, roopa@...dia.com,
        nikolay@...dia.com, jiri@...nulli.us, idosch@...sch.org,
        stephen@...workplumber.org, netdev@...r.kernel.org,
        bridge@...ts.linux-foundation.org
Subject: Re: [RFC net-next 6/9] net: dsa: Forward offloading

On Mon, Apr 26, 2021 at 07:04:08PM +0200, Tobias Waldekranz wrote:
> Allow DSA drivers to support forward offloading from a bridge by:
> 
> - Passing calls to .ndo_dfwd_{add,del}_station to the drivers.
> 
> - Recording the subordinate device of offloaded skbs in the control
>   buffer so that the tagger can take the appropriate action.
> 
> Signed-off-by: Tobias Waldekranz <tobias@...dekranz.com>
> ---
>  include/net/dsa.h |  7 +++++++
>  net/dsa/slave.c   | 36 ++++++++++++++++++++++++++++++++++--
>  2 files changed, 41 insertions(+), 2 deletions(-)
> 
> diff --git a/include/net/dsa.h b/include/net/dsa.h
> index 1f9ba9889034..77d4df819299 100644
> --- a/include/net/dsa.h
> +++ b/include/net/dsa.h
> @@ -119,6 +119,7 @@ struct dsa_netdevice_ops {
>  
>  struct dsa_skb_cb {
>  	struct sk_buff *clone;
> +	struct net_device *sb_dev;
>  };
>  
>  struct __dsa_skb_cb {
> @@ -828,6 +829,12 @@ struct dsa_switch_ops {
>  					  const struct switchdev_obj_ring_role_mrp *mrp);
>  	int	(*port_mrp_del_ring_role)(struct dsa_switch *ds, int port,
>  					  const struct switchdev_obj_ring_role_mrp *mrp);
> +
> +	/* L2 forward offloading */
> +	void *	(*dfwd_add_station)(struct dsa_switch *ds, int port,
> +				    struct net_device *sb_dev);
> +	void	(*dfwd_del_station)(struct dsa_switch *ds, int port,
> +				    struct net_device *sb_dev);
>  };
>  
>  #define DSA_DEVLINK_PARAM_DRIVER(_id, _name, _type, _cmodes)		\
> diff --git a/net/dsa/slave.c b/net/dsa/slave.c
> index 77b33bd161b8..3689ffa2dbb8 100644
> --- a/net/dsa/slave.c
> +++ b/net/dsa/slave.c
> @@ -657,6 +657,13 @@ static netdev_tx_t dsa_slave_xmit(struct sk_buff *skb, struct net_device *dev)
>  	return dsa_enqueue_skb(nskb, dev);
>  }
>  
> +static u16 dsa_slave_select_queue(struct net_device *dev, struct sk_buff *skb,
> +				  struct net_device *sb_dev)
> +{
> +	DSA_SKB_CB(skb)->sb_dev = sb_dev;
> +	return netdev_pick_tx(dev, skb, sb_dev);
> +}
> +

DSA_SKB_CB is going away:
https://patchwork.kernel.org/project/netdevbpf/patch/20210427042203.26258-5-yangbo.lu@nxp.com/

Let's either negotiate with Yangbo on keeping it, or make
.ndo_select_queue a bypass towards the tagger, where it can use its own
SKB_CB structure and be more flexible in general (I think I'm leaning
towards the latter).