linux-kernel - Re: [PATCH v6 1/6] dt-bindings: gpio-mmio: Correct opencores GPIO

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Message-ID: <aXS82qiNNvPVMqdV@antec>
Date: Sat, 24 Jan 2026 12:36:42 +0000
From: Stafford Horne <shorne@...il.com>
To: Gary Lau <zgliu@...mail.com>
Cc: linusw <linusw@...nel.org>, linux-kernel <linux-kernel@...r.kernel.org>,
	linux-openrisc <linux-openrisc@...r.kernel.org>,
	devicetree <devicetree@...r.kernel.org>, robh <robh@...nel.org>,
	krzk+dt <krzk+dt@...nel.org>, conor+dt <conor+dt@...nel.org>,
	geert+renesas <geert+renesas@...der.be>,
	"krzysztof.kozlowski" <krzysztof.kozlowski@....qualcomm.com>,
	brgl <brgl@...nel.org>, linux-gpio <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH v6 1/6] dt-bindings: gpio-mmio: Correct opencores GPIO

On Fri, Jan 23, 2026 at 10:18:04PM +0800, Gary Lau wrote:
> Hi Stafford,
> 
> I should clarify my setup: I'm using hardware address translation to make the
> OpenCores 8-bit GPIO appear as 32-bit to the CPU. Specifically:
> 
> 1. Address translation: The CPU's 32-bit addresses are right-shifted by 2 bits
>    (adr_i[2] in Verilog), so each 32-bit CPU access maps to the correct 8-bit
>    OpenCores register.
> 
> 2. Data width adaptation: Only dat_i[7:0] and dat_o[7:0] are connected, so
>    32-bit writes are truncated to 8-bit, and reads are zero-extended.
> 
> This hardware wrapper makes brcm,bcm6345-gpio driver "work" with my OpenCores
> GPIO, but it's really a hardware-level compatibility layer, not true software
> compatibility.
> 
> So you're absolutely right that the native opencores,gpio isn't compatible
> with brcm,bcm6345-gpio. My setup works because of custom hardware translation,
> not because the IP cores are compatible.

Thanks Gary for testing.

-Stafford