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

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Message-ID: <aV9o1LL0Ahip0O3-@antec>
Date: Thu, 8 Jan 2026 08:20:36 +0000
From: Stafford Horne <shorne@...il.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Linux OpenRISC <linux-openrisc@...r.kernel.org>,
	Linus Walleij <linus.walleij@...aro.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 Wed, Jan 07, 2026 at 03:35:45PM +0100, Geert Uytterhoeven wrote:
> Hi Stafford,
> 
> On Wed, 17 Dec 2025 at 09:15, Stafford Horne <shorne@...il.com> wrote:
> > In FPGA Development boards with GPIOs we use the opencores gpio verilog
> > rtl.  This is compatible with the gpio-mmio.  Add the compatible string
> > to allow as below.
> >
> > Example:
> >
> >         gpio0: gpio@...00000 {
> >                 compatible = "opencores,gpio", "brcm,bcm6345-gpio";
> >                 reg = <0x91000000 0x1>, <0x91000001 0x1>;
> >                 reg-names = "dat", "dirout";
> >                 gpio-controller;
> >                 #gpio-cells = <2>;
> >                 status = "okay";
> >         };
> >
> > Link: https://opencores.org/projects/gpio
> > Signed-off-by: Stafford Horne <shorne@...il.com>
> 
> Thanks for your patch, which is now commit f48b5e8bc2e1344f
> ("dt-bindings: gpio-mmio: Add compatible string for opencores,gpio")
> in gpio/gpio/for-next.
> 
> > --- a/Documentation/devicetree/bindings/gpio/gpio-mmio.yaml
> > +++ b/Documentation/devicetree/bindings/gpio/gpio-mmio.yaml
> > @@ -18,11 +18,16 @@ description:
> >
> >  properties:
> >    compatible:
> > -    enum:
> > -      - brcm,bcm6345-gpio
> > -      - ni,169445-nand-gpio
> > -      - wd,mbl-gpio # Western Digital MyBook Live memory-mapped GPIO controller
> > -      - intel,ixp4xx-expansion-bus-mmio-gpio
> > +    oneOf:
> > +      - enum:
> > +          - brcm,bcm6345-gpio
> > +          - ni,169445-nand-gpio
> > +          - wd,mbl-gpio # Western Digital MyBook Live memory-mapped GPIO controller
> > +          - intel,ixp4xx-expansion-bus-mmio-gpio
> > +      - items:
> > +          - enum:
> > +              - opencores,gpio
> > +          - const: brcm,bcm6345-gpio
> 
> 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...

Hello,

I was following what we did for uart, where we have
"opencores,uart16550-rtlsvn105", "ns16550a".

I am using brcm,bcm6345-gpio to match the drivers/gpio/gpio-mmio.c driver.
The opencores,gpio is compatible with the same driver as brcm,bcm6345-gpio but
not 100% the same as the brcm,bcm6345-gpio.  Since the device tree allows
configuring the gpio-mmio driver to make it compatible with opencore,gpio I
thought this would be OK.

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>;
       };

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?

If so I will can revise this patch and add patch to gpio-mmio.c.

-Stafford