linux-kernel - Re: [PATCH 07/14] dt-bindings: pinctrl: qcom: Add output-enable

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Message-ID: <510cf7ac-3f7f-49e2-b384-424c931b2750@linaro.org>
Date:   Mon, 27 Mar 2023 09:22:45 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Douglas Anderson <dianders@...omium.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>
Cc:     Matthias Kaehlcke <mka@...omium.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        linux-gpio@...r.kernel.org, Stephen Boyd <swboyd@...omium.org>,
        devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-spi@...r.kernel.org, Andy Gross <agross@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 07/14] dt-bindings: pinctrl: qcom: Add output-enable

On 23/03/2023 18:30, Douglas Anderson wrote:
> In the patch ("dt-bindings: pinctrl: qcom: tlmm should use
> output-disable, not input-enable") we allowed setting "output-disable"
> for TLMM pinctrl states. Let's also add "output-enable".
> 
> At first blush this seems a needless thing to do. Specifically:
> - In Linux (and presumably any other OSes using the same device trees)
>   the GPIO/pinctrl driver knows to automatically enable the output
>   when a GPIO is changed to an output. Thus in most cases specifying
>   "output-enable" is superfluous and should be avoided.
> - If we need to set a pin's default state we already have
>   "output-high" and "output-low" and these properties already imply
>   "output-enabled" (at least on the Linux Qualcomm TLMM driver).
> 
> However, there is one instance where "output-enable" seems like it
> could be useful: sleep states. It's not uncommon to want to configure
> pins as inputs (with appropriate pulls) when the driver controlling
> them is in a low power state. Then we want the pins back to outputs
> when the driver wants things running normally. To accomplish this we'd
> want to be able to use "output-enable". Then the "default" state could
> have "output-enable" and the "sleep" state could have
> "output-disable".
> 
> NOTE: in all instances I'm aware of, we'd only want to use
> "output-enable" on pins that are configured as "gpio". The Qualcomm
> documentation that I have access to says that "output-enable" only
> does something useful when in GPIO mode.
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>

Best regards,
Krzysztof