linux-kernel - Re: [PATCH v11 2/6] gpiolib: allow to specify the firmware node in struct gpio

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Message-ID: <CAMRc=MdRMeyzonY+AZa8CWfh6Bk64e3OXAmGk3X=rx=DrM4-mw@mail.gmail.com>
Date:   Tue, 30 Nov 2021 19:32:28 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Kent Gibson <warthog618@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Shuah Khan <shuah@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v11 2/6] gpiolib: allow to specify the firmware node in
 struct gpio_chip

On Tue, Nov 30, 2021 at 5:20 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Tue, Nov 30, 2021 at 06:14:01PM +0200, Andy Shevchenko wrote:
> > On Tue, Nov 30, 2021 at 04:41:23PM +0100, Bartosz Golaszewski wrote:
>
> ...
>
> > Not sure I understand the proposal. Can you provide couple of (simplest)
> > examples?
> >
> > And also it sounds like reinventing a wheel. What problem do you have that you
> > need to solve this way?
>
> Have you seen these:
>         drivers/gpio/gpio-dwapb.c
>         drivers/mfd/intel_quark_i2c_gpio.c
> ?
>
> GPIO driver has a main (controller level) node along with children on per bank
> basis. Currently it works with the provided approach (see second driver).
>
> --
> With Best Regards,
> Andy Shevchenko
>
>

Yep, I know dwapd. What happens in probe is that each bank device is
created using the properties from the associated child fwnode but the
parent device's fwnode is actually assigned as the gpiochip's fwnode.
This is logically wrong and OF doesn't do it - it assigns the child
of_node to the child device if gpio_chip->of_node is assigned in the
driver. I'm not sure if ACPI does this.

Non-OF drivers don't have a way to do this and this patch enables it.

I want to add it mostly because gpio-sim can then use the software
node to identify the device in the configfs by that software node but
IMO this is logically correct too.

Bart