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Message-ID: <510cf7ac-3f7f-49e2-b384-424c931b2750@linaro.org>
Date:   Mon, 27 Mar 2023 09:22:45 +0200
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Subject: Re: [PATCH 07/14] dt-bindings: pinctrl: qcom: Add output-enable
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To:     Douglas Anderson <dianders@chromium.org>,
        Bjorn Andersson <andersson@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Mark Brown <broonie@kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>
Cc:     Matthias Kaehlcke <mka@chromium.org>,
        Konrad Dybcio <konrad.dybcio@linaro.org>,
        linux-gpio@vger.kernel.org, Stephen Boyd <swboyd@chromium.org>,
        devicetree@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        linux-spi@vger.kernel.org, Andy Gross <agross@kernel.org>,
        linux-kernel@vger.kernel.org
References: <20230323173019.3706069-1-dianders@chromium.org>
 <20230323102605.7.I7874c00092115c45377c2a06f7f133356956686e@changeid>
From:   Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
In-Reply-To: <20230323102605.7.I7874c00092115c45377c2a06f7f133356956686e@changeid>
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Precedence: bulk

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@chromium.org>

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

Best regards,
Krzysztof