Re: [PATCH net-next v7 2/8] net: dsa: Give drivers the chance to veto certain upper devices

[Vladimir Oltean <olteanv@gmail.com>]

On Wed, Oct 28, 2020 at 08:42:15AM +0100, Kurt Kanzenbach wrote:
> From: Vladimir Oltean <vladimir.oltean@nxp.com>
> 
> Some switches rely on unique pvids to ensure port separation in
> standalone mode, because they don't have a port forwarding matrix
> configurable in hardware. So, setups like a group of 2 uppers with the
> same VLAN, swp0.100 and swp1.100, will cause traffic tagged with VLAN
> 100 to be autonomously forwarded between these switch ports, in spite
> of there being no bridge between swp0 and swp1.
> 
> These drivers need to prevent this from happening. They need to have
> VLAN filtering enabled in standalone mode (so they'll drop frames tagged
> with unknown VLANs) and they can only accept an 8021q upper on a port as
> long as it isn't installed on any other port too. So give them the
> chance to veto bad user requests.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
> Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
> ---

In case reviewers have doubts about this new DSA operation in general.
I would expect that when LAG support is merged, some drivers will
support it, but not any tx_type, but e.g. just NETDEV_LAG_TX_TYPE_HASH.
So it would also be helpful in that case, so they could veto other types
of bond interfaces cleanly. So I do see the need for a generic
"prechangeupper" operation given to drivers.