From: Vladimir Oltean <olteanv@gmail.com>
Date: Wed, 10 Feb 2021 11:14:41 +0200

From: Vladimir Oltean <vladimir.oltean@nxp.com>

Because the bridge will start offloading SWITCHDEV_ATTR_ID_PORT_BRIDGE_FLAGS
while not serialized by any lock such as the br->lock spinlock, existing
drivers that treat that attribute and cache the brport flags might no
longer work correctly.

The issue is that the brport flags are a single unsigned long bitmask,
and the bridge only guarantees the validity of the changed bits, not the
full state. So when offloading two concurrent switchdev attributes, such
as one for BR_LEARNING and another for BR_FLOOD, it might happen that
the flags having BR_FLOOD are written into the cached value, and this in
turn disables the BR_LEARNING bit which was set previously.

We can fix this across the board by keeping individual boolean variables
for each brport flag. Note that mlxsw and prestera were setting the
BR_LEARNING_SYNC flag too, but that appears to be just dead code, so I
removed it.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>

This needs updating because, as discussed, there is no race.