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

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Message-ID: <tencent_F07E7380CFFB3A6A7480FDA42A636B7D290A@qq.com>
Date: Fri, 23 Jan 2026 22:18:04 +0800
From: "Gary Lau" <zgliu@...mail.com>
To: "Stafford Horne" <shorne@...il.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

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.

Best regards,
Gary