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

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Date:   Tue, 28 Jun 2022 15:29:13 +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 3:23 PM Michael Walle <michael@...le.cc> wrote:
>
> >> 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.
>
> Imagine the following device tree snippet:
>   port0 {
>     reg = <0>;
>     status = "okay";
>   }
>   port1 {
>     reg = <1>;
>     status = "disabled";
>   }
>   port@2 {
>     reg = <2>;
>     status = "okay";
>   }
>
> The driver will set num_phys_ports to 2. When port@2 is probed, it
> will have the (correct!) physical port number 2. That will then
> trigger various EINVAL checks with "port_num >= num_phys_ports" or
> WARN()s.

It means the above mentioned condition is wrong: it should be

"port_idx >= num_phys_ports" (if the port_idx doesn't exists, that's
the bug in the first place)

> So the easiest fix would be to actual count all the child nodes
> (regardless if they are available or not), assuming there are as
> many nodes as physical ports.
>
> But num_phys_ports being a property of the hardware

So, name is wrong, that's how I read it, it should be
num_of_acrive_phys_ports (or alike).

> I don't
> think it's good to deduce it by counting the child nodes anyway,

Right.

> but it should rather be a (hardcoded) property of the driver.

Also good to update.

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

-- 
With Best Regards,
Andy Shevchenko