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Fri, 03 Jan 2025 06:48:24 -0800 (PST) Message-ID: <3e3136e5-cb59-45a8-8bd3-43bf401c14cb@linaro.org> Date: Fri, 3 Jan 2025 14:48:23 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 4/4] arm64: dts: qcom: qcs6490-rb3gen2-vision-mezzanine: Add vision mezzanine To: Vladimir Zapolskiy , Konrad Dybcio , Vikram Sharma , rfoss@kernel.org, todor.too@gmail.com, mchehab@kernel.org, robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org, akapatra@quicinc.com, hariramp@quicinc.com, andersson@kernel.org, konradybcio@kernel.org, hverkuil-cisco@xs4all.nl, cros-qcom-dts-watchers@chromium.org, catalin.marinas@arm.com, will@kernel.org Cc: linux-arm-kernel@lists.infradead.org, linux-media@vger.kernel.org, linux-arm-msm@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, kernel@quicinc.com References: <20241217140656.965235-1-quic_vikramsa@quicinc.com> <20241217140656.965235-5-quic_vikramsa@quicinc.com> <22479c27-9265-4994-8974-9739ecbae5ee@linaro.org> <99cf5f7e-43f6-4ac4-a4a2-dc731b695572@oss.qualcomm.com> Content-Language: en-US From: Bryan O'Donoghue In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 19/12/2024 19:32, Vladimir Zapolskiy wrote: >>>> +        rst-pins { >>>> +            pins = "gpio78"; >>>> +            function = "gpio"; >>>> +            drive-strength = <2>; >>>> +            bias-pull-down; >>>> +            output-low; >>>> +        }; >>> >>> I have doubts that it's proper to embed a reset gpio into driver's >>> pinctrl suspend/resume power management. >>> >>> Konrad, can you please confirm that it's really accepted? >>> >>> I'd rather ask to remove this reset pin control. >> >> There's certainly some appearances of this in the tree. >> >> You could make the argument that it makes sense to prevent >> misconfiguration >> (i.e. the bootloader may set the pin in input mode), but then the counter >> argument is that the (Linux) gpiod APIs request OUT_LOW/HIGH, and we >> would >> expect that the driver uses that if the GPIO is requested through >> e.g. reset-gpios. >> >> I'm not particularly sure what to recommend here. Krzysztof? >> > > I'm worried by a possibility that a device reset/shutdown control GPIO > could > be turned off by entering the "sleep" pinctrl setup. If a particular > GPIO/pin > is off, is it still continuously functional as a control GPIO of some > device? > I believe it is not anymore in general, this is my concern here. I agree for this particular case that rst-pin should be excised. - RST is an active low signal, which is typically _pulsed_ for a period when the sensor is powered to trigger a reset in the state machine of the sensor - What is the use-case of pulling RST down the GPIO in suspend ? I'd remove the output-low though it should make no difference as the sensor regulators will be off. - MCLK I think should have a suspend state specified or at least I can't think of a good reason right now why what I see here is wrong. For the default state this patch disables the GPIO pull down bias, which to me seems logical and correct. TBH I don't have a big concern about the RST pin in reset because the regulators will be off. --- bod