linux-kernel - Re: [PATCH v2 1/5] dt-bindings: Add compatible string opencores,gpio to gpio-mmio

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Message-ID: <CAD++jLm1u9ChqsftwvbOptiG3Qo2KWxPjqN2snOVuZDYuVST5Q@mail.gmail.com>
Date: Fri, 9 Jan 2026 11:07:17 +0100
From: Linus Walleij <linusw@...nel.org>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Stafford Horne <shorne@...il.com>, LKML <linux-kernel@...r.kernel.org>, 
	Linux OpenRISC <linux-openrisc@...r.kernel.org>, Bartosz Golaszewski <brgl@...nel.org>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	linux-gpio@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v2 1/5] dt-bindings: Add compatible string opencores,gpio
 to gpio-mmio

On Thu, Jan 8, 2026 at 9:41 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:

> > > What is the rationale behind using brcm,bcm6345-gpio?
> > > Given brcm,bcm6345-gpio has 32-bit registers, while opencores,gpio
> > > has 8-bit registers, I doubt the latter is compatible with the former...

Yeah this needs to be fixed/reverted pronto :/

> > I switch the size from 32-bit to 8-bit using the reg = <* 0x1>, <* 0x1> setting.
> > Also the reg addresses of "dat" and "dirout" are different for the real
> > brcm,bcm6345-gpio.
> >
> > brcm,bcm6345-gpio. Example:
> >
> >        /* GPIOs 192 .. 223 */
> >        gpio6: gpio@518 {
> >                compatible = "brcm,bcm6345-gpio";
> >                reg = <0x518 0x04>, <0x538 0x04>;
> >                reg-names = "dirout", "dat";
> >                gpio-controller;
> >                #gpio-cells = <2>;
> >        };
> >
> > vs opencores,gpio Example:
> >
> >        gpio0: gpio@...00000 {
> >                compatible = "opencores,gpio", "brcm,bcm6345-gpio";
> >                reg = <0x91000000 0x1>, <0x91000001 0x1>;
> >                reg-names = "dat", "dirout";
> >                gpio-controller;
> >                #gpio-cells = <2>;
> >        };
>
> Exactly, the register space and register widths are different

...as proved here.

Stafford can you send a fixup or revert patch?
(Only need to revert if you can't make a fix quick enough, which I
think you can.)

> > The opencores,gpio setup does work.
> >
> > Now that I think about it, would it have been better to just add opencores,gpio
> > to gpio-mmio.c compatible list?
>
> I think that would be better.

Yes this is better.

I should have seen this, I guess I was sloppy :(

> > If so I will can revise this patch and add patch to gpio-mmio.c.
>
> DT maintainers: Given gpio-mmio is that generic/simple, is there a
> specific reason there is no generic "gpio-mmio" compatible value that
> can be used as a fallback, avoiding the need to keep on adding new
> entries to gpio_mmio_of_match[]?

I think "gpio-mmio" combined with compulsory property of
bus-width = <nn> (as used by multiple bindings) would be
generic enough. So a schema that accepts "gpio-mmio" if and
only if bus-width = 8|16|32|64 would be acceptable.

Yours,
Linus Walleij