Re: [PATCH v3 net-next 09/14] net: dsa: Validate hardware support for MST

[Vladimir Oltean <olteanv@gmail.com>]

On Mon, Mar 14, 2022 at 10:52:26AM +0100, Tobias Waldekranz wrote:
> When joining a bridge where MST is enabled, we validate that the
> proper offloading support is in place, otherwise we fallback to
> software bridging.
> 
> When then mode is changed on a bridge in which we are members, we
> refuse the change if offloading is not supported.
> 
> At the moment we only check for configurable learning, but this will
> be further restricted as we support more MST related switchdev events.
> 
> Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
> ---
>  net/dsa/dsa_priv.h |  2 ++
>  net/dsa/port.c     | 20 ++++++++++++++++++++
>  net/dsa/slave.c    |  6 ++++++
>  3 files changed, 28 insertions(+)
> 
> diff --git a/net/dsa/dsa_priv.h b/net/dsa/dsa_priv.h
> index f20bdd8ea0a8..2aba420696ef 100644
> --- a/net/dsa/dsa_priv.h
> +++ b/net/dsa/dsa_priv.h
> @@ -234,6 +234,8 @@ int dsa_port_vlan_filtering(struct dsa_port *dp, bool vlan_filtering,
>  			    struct netlink_ext_ack *extack);
>  bool dsa_port_skip_vlan_configuration(struct dsa_port *dp);
>  int dsa_port_ageing_time(struct dsa_port *dp, clock_t ageing_clock);
> +int dsa_port_mst_enable(struct dsa_port *dp, bool on,
> +			struct netlink_ext_ack *extack);
>  int dsa_port_mtu_change(struct dsa_port *dp, int new_mtu,
>  			bool targeted_match);
>  int dsa_port_fdb_add(struct dsa_port *dp, const unsigned char *addr,
> diff --git a/net/dsa/port.c b/net/dsa/port.c
> index 58291df14cdb..1a17a0efa2fa 100644
> --- a/net/dsa/port.c
> +++ b/net/dsa/port.c
> @@ -240,6 +240,10 @@ static int dsa_port_switchdev_sync_attrs(struct dsa_port *dp,
>  	if (err && err != -EOPNOTSUPP)
>  		return err;
>  
> +	err = dsa_port_mst_enable(dp, br_mst_enabled(br), extack);
> +	if (err && err != -EOPNOTSUPP)
> +		return err;

The "err && err != -EOPNOTSUPP" scheme is in place for compatibility
with drivers that don't all support the bridge port attributes, but used
to work prior to dsa_port_switchdev_sync_attrs()'s existence.

I don't think this scheme is necessary for dsa_port_mst_enable(), you
can just return -EOPNOTSUPP and remove the special handling for this code.

> +
>  	return 0;
>  }
>  
> @@ -735,6 +739,22 @@ int dsa_port_ageing_time(struct dsa_port *dp, clock_t ageing_clock)
>  	return 0;
>  }
>  
> +int dsa_port_mst_enable(struct dsa_port *dp, bool on,
> +			struct netlink_ext_ack *extack)
> +{
> +	struct dsa_switch *ds = dp->ds;
> +
> +	if (!on)
> +		return 0;
> +
> +	if (!dsa_port_can_configure_learning(dp)) {
> +		NL_SET_ERR_MSG_MOD(extack, "Hardware does not support MST");
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
>  int dsa_port_pre_bridge_flags(const struct dsa_port *dp,
>  			      struct switchdev_brport_flags flags,
>  			      struct netlink_ext_ack *extack)
> diff --git a/net/dsa/slave.c b/net/dsa/slave.c
> index a61a7c54af20..333f5702ea4f 100644
> --- a/net/dsa/slave.c
> +++ b/net/dsa/slave.c
> @@ -463,6 +463,12 @@ static int dsa_slave_port_attr_set(struct net_device *dev, const void *ctx,
>  
>  		ret = dsa_port_ageing_time(dp, attr->u.ageing_time);
>  		break;
> +	case SWITCHDEV_ATTR_ID_BRIDGE_MST:
> +		if (!dsa_port_offloads_bridge_dev(dp, attr->orig_dev))
> +			return -EOPNOTSUPP;
> +
> +		ret = dsa_port_mst_enable(dp, attr->u.mst, extack);
> +		break;
>  	case SWITCHDEV_ATTR_ID_PORT_PRE_BRIDGE_FLAGS:
>  		if (!dsa_port_offloads_bridge_port(dp, attr->orig_dev))
>  			return -EOPNOTSUPP;
> -- 
> 2.25.1
>