netdev - Re: [PATCH net-next v2 1/2] net: dsa: mv88e6xxx: Save switch rules

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Date:   Mon, 28 Jan 2019 15:24:56 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Gregory Clement <gregory.clement@...tlin.com>,
        Antoine Tenart <antoine.tenart@...tlin.com>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Nadav Haklai <nadavh@...vell.com>
Subject: Re: [PATCH net-next v2 1/2] net: dsa: mv88e6xxx: Save switch rules

Hi Florian,

Florian Fainelli <f.fainelli@...il.com> wrote on Fri, 25 Jan 2019
10:37:38 -0800:

> Hi Miquel,
> 
> On 1/25/19 1:55 AM, Miquel Raynal wrote:
> > The user might apply a specific switch configuration, with specific
> > forwarding rules, VLAN, bridges, etc.
> > 
> > During suspend to RAM the switch power will be turned off and the
> > switch will lost its configuration. In an attempt to bring S2RAM
> > support to the mv88e6xxx DSA, let's first save these rules in a
> > per-chip list thanks to the mv88e6xxx_add/del_xxx_rule()
> > helpers. These helpers are then called from various callbacks:
> > * mv88e6xxx_port_fdb_add/del()
> > * mv88e6xxx_port_mdb_add/del()
> > * mv88e6xxx_port_vlan_add/del()
> > * mv88e6xxx_port_bridge_join/leave()
> > * mv88e6xxx_crosschip_bridge_join/leave()
> > 
> > To avoid recursion problems when replaying the rules, the content of
> > the above *_add()/*_join() callbacks has been moved in separate
> > helpers with a '_' prefix. Hence, each callback just calls the
> > corresponding helper and the corresponding *_add_xxx_rule().  
> 
> None of this should be done in the driver IMHO, because this is
> presumably applicable to all switch devices that lose their state during
> suspend/resume, so at best, this should be moved to the core DSA layer,
> but doing this means that we should also have a well established
> contract between the DSA layer and individual switch drivers as far as
> quiescing/saving/restoring state goes.
> 
> By moving things to the core we can also more tightly control what data
> structures get used to represent e.g.: VLANs, FDBs, MDBs etc and
> possibly push/utilize caching into the original subsystem. For instance
> VLAN/bridge already do maintain caches of VLANs, so if we could somehow
> expose those, we would not bloat the kernel's memory footprint by having
> an additional layer to maintain with identical information.

So you suggest to move the intelligence of FDBs/MDBs in net/dsa/port.c,
is this right?

I don't see where VLAN and bridge information are cached, can you point
me to the relevant locations?

What about cross-chip bridges? There is nothing about them in
net/dsa/port.c. The implementation I see in the mv88e6xxx driver
only touches the PVT but I don't get whether we should handle this
calls like regular bridge-join/leave events or not (maybe they are
cached with regular bridge events?).


Thanks,
Miquèl