linux-kernel - Re: [PATCH v4 2/2] gpio: Add Realtek Otto GPIO support

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Message-ID: <CAHp75VftETTkOGx6AUvQi5s-ngo73WBdHnqsX84pCM6GAaHMyQ@mail.gmail.com>
Date:   Tue, 30 Mar 2021 13:14:36 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Sander Vanheule <sander@...nheule.net>
Cc:     devicetree <devicetree@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Bert Vermeulen <bert@...t.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Marc Zyngier <maz@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v4 2/2] gpio: Add Realtek Otto GPIO support

On Mon, Mar 29, 2021 at 8:28 PM Sander Vanheule <sander@...nheule.net> wrote:
> On Mon, 2021-03-29 at 13:26 +0300, Andy Shevchenko wrote:
> > On Fri, Mar 26, 2021 at 11:11 PM Sander Vanheule <
> > sander@...nheule.net> wrote:

...

> > AFAICS all, except one have this flag, I suggest you to do other way
> > around, i.e. check compatible string in the code. Or do something more
> > clever. What happens if you have this flag enabled for the fallback
> > node?
> >
> > If two people ask the same, it might be a smoking gun.
> >
>
> Testing for the fallback wouldn't work, since of_device_is_compatible()
> would always match. Setting the (inverse) flag only on the fallback
> would indeed reduce the clutter.
>
> If the port order is reversed w.r.t. to the current implementation,
> enabling a GPIO+IRQ would enable the same pin on a different port. I
> don't think the result would be catastrophical, but it would result in
> unexpected behaviour. When A0 and C0 are then enabled, A0 interrupts
> would actually come from C0, and vice versa.
>
>    Intended port | A | B | C | D
> -----------------+---+---+---+---
> Actual GPIO port | D | C | B | A
>  Actual IRQ port | B | A | D | C
>
> If only the actual GPIO ports change, at least you can still use a
> modified GPIO line number and polling. The user could just leave out
> the optional irq-controller from the devicetree, but I would rather
> have it enforced in some way.

OK! Thanks for clarification.

-- 
With Best Regards,
Andy Shevchenko