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From:   Marcin Wojtas <mw@semihalf.com>
Date:   Thu, 28 Jul 2022 08:52:04 +0200
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Subject: Re: [net-next: PATCH v3 6/8] net: core: switch to fwnode_find_net_device_by_node()
To:     Andy Shevchenko <andy.shevchenko@gmail.com>
Cc:     Vladimir Oltean <olteanv@gmail.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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=C5=9Br., 27 lip 2022 o 23:15 Andy Shevchenko <andy.shevchenko@gmail.com> n=
apisa=C5=82(a):
>
>
>
> On Wednesday, July 27, 2022, Marcin Wojtas <mw@semihalf.com> wrote:
>>
>> =C5=9Br., 27 lip 2022 o 18:38 Vladimir Oltean <olteanv@gmail.com> napisa=
=C5=82(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 mak=
e
>> > anyway.  I see that mvpp2 also needed commit c4053ef32208 ("net: mvpp2=
:
>> > initialize port of_node pointer"), but that isn't needed in general, a=
nd
>> > 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 ene=
tc).
>>
>> >
>> > > 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 mat=
ter.
>> > The point is that you'd be mistaken to think that only the drivers whi=
ch
>> > 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.
>
>
>
> Fixing how?!
>
>
>>
>>
>> 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 =3D dev->parent) {
>>                 if (device_match_fwnode(dev, data))
>>                         return 1;
>> +               else if (device_match_of_node(dev, to_of_node(data))
>> +                       return 1;
>>         }
>>
>
> This adds a piece of dead code. device_match_fwnode() covers this already=
.
>

Yes, indeed. After recent update, I think we can assume the current
implementation of fwnode_find_parent_dev_match should work fine with
all existing cases.

Thank you for all remarks and comments, I'll address them in v4 later today=
.

Best regards,
Marcin