Re: [PATCH v4 net-next 10/15] net: dsa: Validate hardware support for MST

[Vladimir Oltean <olteanv@gmail.com>]

On Tue, Mar 15, 2022 at 01:25:38AM +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     | 22 ++++++++++++++++++++++
>  net/dsa/slave.c    |  6 ++++++
>  3 files changed, 30 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..02214033cec0 100644
> --- a/net/dsa/port.c
> +++ b/net/dsa/port.c
> @@ -321,6 +321,11 @@ static void dsa_port_bridge_destroy(struct dsa_port *dp,
>  	kfree(bridge);
>  }
>  
> +static bool dsa_port_supports_mst(struct dsa_port *dp)
> +{
> +	return dsa_port_can_configure_learning(dp);
> +}
> +
>  int dsa_port_bridge_join(struct dsa_port *dp, struct net_device *br,
>  			 struct netlink_ext_ack *extack)
>  {
> @@ -334,6 +339,9 @@ int dsa_port_bridge_join(struct dsa_port *dp, struct net_device *br,
>  	struct net_device *brport_dev;
>  	int err;
>  
> +	if (br_mst_enabled(br) && !dsa_port_supports_mst(dp))
> +		return -EOPNOTSUPP;
> +
>  	/* Here the interface is already bridged. Reflect the current
>  	 * configuration so that drivers can program their chips accordingly.
>  	 */
> @@ -735,6 +743,20 @@ 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)
> +{
> +	if (!on)
> +		return 0;
> +
> +	if (!dsa_port_supports_mst(dp)) {
> +		NL_SET_ERR_MSG_MOD(extack, "Hardware does not support MST");
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}

Experimenting a bit... maybe this looks tidier? We make the "if" condition
have the same basic structure as the previous "if (br_mst_enabled(br) &&
!dsa_port_supports_mst(dp))", albeit transformed using De Morgan's rules.

{
	if (!on || dsa_port_supports_mst(dp))
		return 0;

	NL_SET_ERR_MSG_MOD(extack, "Hardware does not support MST");
	return -EINVAL;
}

> +
>  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 647adee97f7f..879d18cc99cb 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
>