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

[Andrew Lunn <andrew@lunn.ch>]

On Wed, Oct 28, 2020 at 12:43:44PM +0200, Vladimir Oltean wrote:
> 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.

There is always the interesting question, do we want to veto, or
simply not accelerate it? We will want to consider that case by case.

       Andrew