netdev - Re: [PATCH net-next 3/6] net: dsa: Delete the VID from the upstream port as well

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Date:   Wed, 21 Aug 2019 12:51:32 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Vivien Didelot <vivien.didelot@...il.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>, Ido Schimmel <idosch@...sch.org>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        nikolay@...ulusnetworks.com,
        "David S. Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 3/6] net: dsa: Delete the VID from the upstream
 port as well

On Wed, 21 Aug 2019 at 06:30, Vivien Didelot <vivien.didelot@...il.com> wrote:
>
> On Wed, 21 Aug 2019 01:09:39 +0300, Vladimir Oltean <olteanv@...il.com> wrote:
> > I mean I made an argument already for the hack in 4/6 ("Don't program
> > the VLAN as pvid on the upstream port"). If the hack gets accepted
> > like that, I have no further need of any change in the implicit VLAN
> > configuration. But it's still a hack, so in that sense it would be
> > nicer to not need it and have a better amount of control.
>
> How come you simply cannot ignore the PVID flag for the CPU port in the
> driver directly, as mv88e6xxx does in preference of the Marvell specific
> "unmodified" mode? What PVID are you programming on the CPU port already?
>
>
> Thanks,
>
>         Vivien

sja1105 has no such thing as an "unmodified" egress policy.
And ignoring the flags in the switch driver for the CPU port is just
as hacky as fixing it up in the DSA core.
I fail to see any reason to change the pvid for the CPU/DSA ports,
maybe you can clarify.

Actually I gave a second thought to the patchset and in a weird,
convoluted way, I can get away with just:
- 2/6: net: bridge: Populate the pvid flag in br_vlan_get_info
- 5/6 net: dsa: Allow proper internal use of VLANs
- 6/6 net: dsa: tag_8021q: Restore bridge pvid when enabling vlan_filtering
A side effect of running dsa_port_restore_pvid on a user port will be
that it is going to also restore the pvid on the CPU port, via the
bitmap operations. I had not thought of this initially when I first
jumped to remove the BRIDGE_VLAN_INFO_PVID flag in 4/6. And the fact
that it would work would just be "programming by coincidence".

I guess my aversion against the VLAN bitmap operations (and, well,
"match" in your new change) stems from the fact that the DSA core sits
in the way of doing custom configuration of the CPU port VLAN
settings. Yes, you can work around it (dsa_8021q first configures the
user ports as pvid and egress untagged, then configures the CPU port
as egress tagged, so that the pvid setting from user ports doesn't
"stick" to the CPU via the bitmap), but it's like pouring water that's
half hot and half cold from a water cooler, when all you want is water
that's at room temperature.

-Vladimir