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

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Date:   Wed, 27 Jul 2022 19:40:00 +0200
From:   Marcin Wojtas <mw@...ihalf.com>
To:     Vladimir Oltean <olteanv@...il.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()

śr., 27 lip 2022 o 18:38 Vladimir Oltean <olteanv@...il.com> napisał(a):
>
> 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.

SET_NETDEV_DEV() fills net_device->dev.parent with &pdev->dev
and in most cases it is sufficient apparently it is sufficient for
fwnode_find_parent_dev_match (at least tests with mvneta case proves
it's fine).

We have some corner cases though:
* mvpp2 -> single controller can handle up to 3 net_devices and
therefore we need device_set_node() to make this work. I think dpaa2
is a similar case
* PCIE drivers with extra DT description (I think that's the case of enetc).

>
> > 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.

As above - SET_NETDEV_DEV() should be fine in most cases, but we can
never be 100% sure untils it's verified.

>
> > 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).

Can you please check applying following diff:

--- a/drivers/base/property.c
+++ b/drivers/base/property.c
@@ -695,20 +695,22 @@ EXPORT_SYMBOL_GPL(fwnode_get_nth_parent);
  * The routine can be used e.g. as a callback for class_find_device().
  *
  * Returns: %1 - match is found
  *          %0 - match not found
  */
 int fwnode_find_parent_dev_match(struct device *dev, const void *data)
 {
        for (; dev; dev = dev->parent) {
                if (device_match_fwnode(dev, data))
                        return 1;
+               else if (device_match_of_node(dev, to_of_node(data))
+                       return 1;
        }

        return 0;
 }
 EXPORT_SYMBOL_GPL(fwnode_find_parent_dev_match);

Thanks for the review and test.
Marcin