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Received: from DM4PR18MB4144.namprd18.prod.outlook.com (2603:10b6:5:38b::8) by PH7PR18MB5666.namprd18.prod.outlook.com (2603:10b6:510:2e7::16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9913.11; Wed, 13 May 2026 08:59:10 +0000 Received: from DM4PR18MB4144.namprd18.prod.outlook.com ([fe80::cb97:ca8a:e55a:b11]) by DM4PR18MB4144.namprd18.prod.outlook.com ([fe80::cb97:ca8a:e55a:b11%6]) with mapi id 15.20.9913.009; Wed, 13 May 2026 08:59:10 +0000 Message-ID: Date: Wed, 13 May 2026 10:59:04 +0200 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/3] dt-bindings: gpio: add Axiado SGPIO controller Content-Language: en-GB To: Linus Walleij Cc: Tzu-Hao Wei , Swark Yang , Prasad Bolisetty , Bartosz Golaszewski , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Harshit Shah , SriNavmani A , linux-gpio@vger.kernel.org, devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20260414-axiado-ax3000-sgpio-controller-v1-0-b5c7e4c2e69b@axiado.com> <20260414-axiado-ax3000-sgpio-controller-v1-1-b5c7e4c2e69b@axiado.com> <106b7b64-ed6e-499f-b5ac-60c1277f2f03@axiado.com> From: Petar Stepanovic In-Reply-To: Content-Type: text/plain; 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That is the only thing that matters. If they in the end control > the same physical entitiy, it *is* the same GPIO line from Linux' > point of view. No, they are not connected to the same physical line/pin. DIN and DOUT are separate physical SGPIO signals in this hardware. DIN signals are input-only and DOUT signals are output-only; they are not bidirectional or interchangeable paths for the same physical pin. So I agree that Linux should model physical GPIO entities rather than internal register bits. My previous wording was not clear enough: the intention was to describe separate physical SGPIO signals, not just separate register fields. >> Because the direction is fixed by hardware, the standard >> lines-initial-states property, which encodes both direction and initial state, >> does not map cleanly to this design. > GPIOs with fixed direction is nothing new for Linux, we've had > that for ages. > > I would just have the driver reject configurations that does > not apply and bail out. > > If you absolutely want to enforce the lines-initial-states to match what the > hardware can do, then use YAML schema restriuctions on what > values can be encoded into that array. > >> For the output lines (DOUT), should their initial values be described in the >> device tree, or should they be configured by userspace, with the driver only >> providing default initialization? > I don't see why userspace should deal with that. The Linux userspace > ABI is for hacking and odd usecases (like industrial). The nominal > use is kernel-internal consumers and those must be able to > request their GPIOs as well without any userspace shenanigans. > > But avoiding to deal with initial line states at all is a solution > of course. > > What I don't understand is what purpose this dout-init actually > does and why it cannot be set dynamically by the driver at runtime. Some SGPIO outputs may control host-critical signals. For example, if the BMC reboots while the host/server remains powered on, changing SGPIO output values during driver initialization could potentially reset or shut down the running host. The purpose of `dout-init` is to provide a deterministic safe output state during SGPIO initialization, before any GPIO consumer has requested the line. That said, if the preferred approach is to preserve the existing hardware DOUT state during probe and only change the value when a GPIO consumer requests the line, I can rework the driver in that direction. Thnaks, Petar