Re: [PATCH net-next v3 3/3] net: dsa: rzn1-a5psw: add vlan support

[Vladimir Oltean <olteanv@gmail.com>]

On Wed, Feb 08, 2023 at 09:38:04AM -0800, Florian Fainelli wrote:
> > +	/* Enable TAG always mode for the port, this is actually controlled
> > +	 * by VLAN_IN_MODE_ENA field which will be used for PVID insertion
> > +	 */
> > +	reg = A5PSW_VLAN_IN_MODE_TAG_ALWAYS;
> > +	reg <<= A5PSW_VLAN_IN_MODE_PORT_SHIFT(port);
> > +	a5psw_reg_rmw(a5psw, A5PSW_VLAN_IN_MODE, A5PSW_VLAN_IN_MODE_PORT(port),
> > +		      reg);
> 
> If we always enable VLAN mode, which VLAN ID do switch ports not part of a
> VLAN aware bridge get classified into?

Good question. I'd guess 0, since otherwise, the VLAN-unaware FDB
entries added with a5psw_port_fdb_add() wouldn't work.

But the driver has to survive the following chain of commands, which, by
looking at the current code structure, it doesn't:

ip link add br0 type bridge vlan_filtering 0
ip link set swp0 master br0 # PVID should remain at a value chosen privately by the driver
bridge vlan add dev swp0 vid 100 pvid untagged # PVID should not change in hardware yet
ip link set br0 type bridge vlan_filtering 1 # PVID should change to 100 now
ip link set br0 type bridge vlan_filtering 0 # PVID should change to the value chosen by the driver

Essentially, what I'm saying is that VLANs added with "bridge vlan add"
should only be active while vlan_filtering=1.

If you search for "commit_pvid" in drivers/net/dsa, you'll find a number
of drivers which have a more elaborate code structure which allows the
commands above to work properly.