net: dsa: mxl862xx: implement bridge offloading

net: dsa: mxl862xx: implement bridge offloading

Implement joining and leaving bridges as well as add, delete and dump
operations on isolated FDBs, port MDB membership management, and
setting a port's STP state.

The switch supports a maximum of 63 bridges, however, up to 12 may
be used as "single-port bridges" to isolate standalone ports.
Allowing up to 48 bridges to be offloaded seems more than enough on
that hardware, hence that is set as max_num_bridges.

A total of 128 bridge ports are supported in the bridge portmap, and
virtual bridge ports have to be used eg. for link-aggregation, hence
potentially exceeding the number of hardware ports.

The firmware-assigned bridge identifier (FID) for each offloaded bridge
is stored in an array used to map DSA bridge num to firmware bridge ID,
avoiding the need for a driver-private bridge tracking structure.
Bridge member portmaps are rebuilt on join/leave using
dsa_switch_for_each_bridge_member().

As there are now more users of the BRIDGEPORT_CONFIG_SET API and the
state of each port is cached locally, introduce a helper function
mxl862xx_set_bridge_port(struct dsa_switch *ds, int port) which
applies the cached per-port state to hardware. For standalone user
ports (dp->bridge == NULL), it additionally resets the port to
single-port bridge state: CPU-only portmap, learning and flooding
disabled. The CPU port path sets its state explicitly before calling
this helper and is therefore not affected by the reset.

Note that MASK_VLAN_BASED_MAC_LEARNING is intentionally absent from
the firmware write mask. After mxl862xx_reset(), the firmware
initialises all VLAN-based MAC learning fields to 0 (disabled), so
SVL is the active mode by default without having to set it explicitly.

Note that there is no convenient way to control flooding on per-port
level, so the driver is using a 0-rate QoS meter setup as a stopper in
lack of any better option. In order to be perfect the firmware-enforced
minimum bucket size is bypassed by directly writing 0s to the relevant
registers -- without that at least one 64-byte packet could still
pass before the meter would change from 'yellow' into 'red' state.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Link: https://patch.msgid.link/dd079180e2098e5f9626fcd149b9bad9a1b5a1b2.1775049897.git.daniel@makrotopia.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>