linux-kernel - Re: [PATCH 0/3] Fix for KSZ DSA switch shutdown

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Date:   Sat, 11 Sep 2021 14:44:30 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>
Cc:     Lino Sanfilippo <LinoSanfilippo@....de>,
        Saravana Kannan <saravanak@...gle.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>, p.rosenberger@...bus.com,
        woojung.huh@...rochip.com, UNGLinuxDriver@...rochip.com,
        vivien.didelot@...il.com, davem@...emloft.net, kuba@...nel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] Fix for KSZ DSA switch shutdown

On Fri, Sep 10, 2021 at 05:58:52PM +0300, Vladimir Oltean wrote:
> On Fri, Sep 10, 2021 at 01:51:56PM +0200, Andrew Lunn wrote:
> > > It does not really scale but we also don't have that many DSA masters to
> > > support, I believe I can name them all: bcmgenet, stmmac, bcmsysport, enetc,
> > > mv643xx_eth, cpsw, macb.
> > 
> > fec, mvneta, mvpp2, i210/igb.
> 
> I can probably double that list only with Freescale/NXP Ethernet
> drivers, some of which are not even submitted to mainline. To name some
> mainline drivers: gianfar, dpaa-eth, dpaa2-eth, dpaa2-switch, ucc_geth.
> Also consider that DSA/switchdev drivers can also be DSA masters of
> their own, we have boards doing that too.
> 
> Anyway, I've decided to at least try and accept the fact that DSA
> masters will unregister their net_device on shutdown, and attempt to do
> something sane for all DSA switches in that case.
> 
> Attached are two patches (they are fairly big so I won't paste them
> inline, and I would like initial feedback before posting them to the
> list).
> 
> As mentioned in those patches, the shutdown ordering guarantee is still
> very important, I still have no clue what goes on there, what we need to
> do, etc.

So to answer my own question, there is a comment above device_link_add:

 * A side effect of the link creation is re-ordering of dpm_list and the
 * devices_kset list by moving the consumer device and all devices depending
 * on it to the ends of these lists (that does not happen to devices that have
 * not been registered when this function is called).

so the fact that DSA uses device_link_add towards its master is not
exactly for nothing. device_shutdown() walks devices_kset from the back,
so this is our guarantee that DSA's shutdown happens before the master's
shutdown.

So these patches should be okay. Any other comments? If not, I will
formally submit them tomorrow towards the net tree.