linux-kernel - Re: fwnode_for_each_child_node() and OF backend discrepancy

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Message-ID: <CAHp75Vd6e3WwHPfyL=GP=vsoWhwGXadwQziiRRwfHPfjkX2eFg@mail.gmail.com>
Date:   Tue, 28 Jun 2022 15:11:24 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Michael Walle <michael@...le.cc>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: fwnode_for_each_child_node() and OF backend discrepancy

On Tue, Jun 28, 2022 at 1:54 PM Michael Walle <michael@...le.cc> wrote:
>
> Am 2022-06-28 13:10, schrieb Andy Shevchenko:
> > On Mon, Jun 27, 2022 at 02:49:51PM +0200, Michael Walle wrote:
> >> Hi,
> >>
> >> I tired to iterate over all child nodes, regardless if they are
> >> available
> >> or not. Now there is that handy fwnode_for_each_child_node() (and the
> >> fwnode_for_each_available_child_node()). The only thing is the OF
> >> backend
> >> already skips disabled nodes [1], making fwnode_for_each_child_node()
> >> and
> >> fwnode_for_each_available_child_node() behave the same with the OF
> >> backend.
> >>
> >> Doesn't seem to be noticed by anyone for now. I'm not sure how to fix
> >> that
> >> one. fwnode_for_each_child_node() and also
> >> fwnode_get_next_child_node() are
> >> used by a handful of drivers. I've looked at some, but couldn't decide
> >> whether they really want to iterate over all child nodes or just the
> >> enabled
> >> ones.
> >>
> >> Any thoughts?
> >
> > It was discussed at least twice this year (in regard to some new IIO
> > drivers)
> > and Rob told that iterating over disabled (not available) nodes in OF
> > kinda
> > legacy/design mistake. That's why device_for_each_child_node() goes
> > only
> > over available nodes only.
>
> Mh, but then the fwnode_for_each_child_node() is very misleading, esp.
> with the presence of fwnode_for_each_available_child_node().
>
> > So, why do you need to iterate over disabled ones?
>
> I was trying to fix the lan966x driver [1] which doesn't work if there
> are disabled nodes in between.

Can you elaborate what's wrong now in the behaviour of the driver? In
the code it uses twice the _available variant.

> My steps would have been:
>   (1) change fwnode_for_each_available_child_node() to
>       fwnode_for_each_child_node(), maybe with a fixes tag, as it's
>       easy to backport
>   (2) introduce new compatibles and deduce the number of ports
>       according to the compatible string and not by counting
>       the child nodes.
>   (3) keep the old behavior for the legacy compatible and mark it
>       as deprecated in the binding
>   (4) move the device tree over to the new compatible string

> [1]
> https://elixir.bootlin.com/linux/v5.19-rc4/source/drivers/net/ethernet/microchip/lan966x/lan966x_main.c


-- 
With Best Regards,
Andy Shevchenko