linux-kernel - Re: [PATCH v1 2/4] gpio: dwapb: Read GPIO base from gpio-base property

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Date:   Wed, 11 Aug 2021 14:37:42 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>
Cc:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Lee Jones <lee.jones@...aro.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Hoan Tran <hoan@...amperecomputing.com>,
        Serge Semin <fancer.lancer@...il.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH v1 2/4] gpio: dwapb: Read GPIO base from gpio-base property

On Mon, Jul 26, 2021 at 2:54 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:

> For backward compatibility with some legacy devices introduce
> a new (*) property gpio-base to read GPIO base. This will allow
> further cleanup of the driver.
>
> *) Note, it's not new for GPIO library since mockup driver is
>    using it already.
>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
(...)
> -               pp->gpio_base   = -1;
> +               if (fwnode_property_read_u32(fwnode, "gpio-base", &pp->gpio_base))
> +                       pp->gpio_base = -1;

This is problematic because we have repeatedly NACKed this property
to be added to device trees.

I don't know about fwnode policies, but in the device tree this would have
to be "linux,gpio-base" and then it would be NACKed because of adding
an operating-system specific thing to a OS-independent hardware
description.

I don't know what to do with this really, but I understand the need of it
as a kernel-internal thing, however I am afraid that adding this will make
it possible to add linux,gpio-base = <n> to any device tree gpio_chip
as well and that encourages bad behaviour even if we don't allow a
DT binding (YAML) like that.

Is there a way to make a fwnode property only come from software
nodes and not allowed to be used in ACPI or DT? (I guess not...)

Yours,
Linus Walleij