linux-kernel - Re: [net-next: PATCH v3 6/8] net: core: switch to fwnode_find_net_device_by

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Message-ID: <20220727163848.f4e2b263zz3vl2hc@skbuf>
Date:   Wed, 27 Jul 2022 19:38:48 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Marcin Wojtas <mw@...ihalf.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Grzegorz Bernacki <gjb@...ihalf.com>,
        Grzegorz Jaszczyk <jaz@...ihalf.com>,
        Tomasz Nowicki <tn@...ihalf.com>,
        Samer El-Haj-Mahmoud <Samer.El-Haj-Mahmoud@....com>,
        upstream@...ihalf.com
Subject: Re: [net-next: PATCH v3 6/8] net: core: switch to
 fwnode_find_net_device_by_node()

On Wed, Jul 27, 2022 at 05:18:16PM +0200, Marcin Wojtas wrote:
> Do you mean a situation analogous to what I addressed in:
> [net-next: PATCH v3 4/8] net: mvpp2: initialize port fwnode pointer
> ?

Not sure if "analogous" is the right word. My estimation is that the
overwhelmingly vast majority of DSA masters can be found by DSA simply
due to the SET_NETDEV_DEV() call that the Ethernet drivers need to make
anyway.  I see that mvpp2 also needed commit c4053ef32208 ("net: mvpp2:
initialize port of_node pointer"), but that isn't needed in general, and
I can't tell you exactly why it is needed there, I don't know enough
about the mvpp2 driver.

> I found indeed a couple of drivers that may require a similar change
> (e.g. dpaa2).

There I can tell you why the dpaa2-mac code mangles with net_dev->dev.of_node,
but I'd rather not go into an explanation that essentially doesn't matter.
The point is that you'd be mistaken to think that only the drivers which
touch the net device's ->dev->of_node are the ones that need updating
for your series to not cause regressions.

> IMO we have 2 options:
> - update these drivers
> - add some kind of fallback? If yes, I am wondering about an elegant
> solution - maybe add an extra check inside
> fwnode_find_parent_dev_match?
> 
> What would you suggest?

Fixing fwnode_find_parent_dev_match(), of course. This change broke DSA
on my LS1028A system (master in drivers/net/ethernet/freescale/enetc/)
and LS1021A (master in drivers/net/ethernet/freescale/gianfar.c).