Linux Ethernet Bridging - Mar 2022 - [Bridge] [PATCH v3 net-next 09/14] net: dsa: Validate hardware support for MST

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 at 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;
Sadly this will break down because we don't have unwinding on error in
place (sorry). We'd end up with an unoffloaded bridge port with
partially synced bridge port attributes. Could you please add a patch
previous to this one that handles this, and unoffloads those on error?
> +
>  	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
>

On Mon, Mar 14, 2022 at 06:56:49PM +0200, Vladimir Oltean
wrote:
> > 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;
> 
> Sadly this will break down because we don't have unwinding on error in
> place (sorry). We'd end up with an unoffloaded bridge port with
> partially synced bridge port attributes. Could you please add a patch
> previous to this one that handles this, and unoffloads those on error?
Actually I would rather rename the entire dsa_port_mst_enable() function
to dsa_port_mst_validate() and move it to the beginning of
dsa_port_bridge_join().
This simplifies the unwinding that needs to take place quite a bit.