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Date:   Thu, 8 Dec 2022 23:33:54 +0000
From:   Matthias Kaehlcke <mka@chromium.org>
To:     Douglas Anderson <dianders@chromium.org>
Cc:     Bjorn Andersson <andersson@kernel.org>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        swboyd@chromium.org, linux-arm-msm@vger.kernel.org,
        linux-input@vger.kernel.org,
        Yunlong Jia <ecs.beijing2022@gmail.com>,
        Konrad Dybcio <konrad.dybcio@linaro.org>,
        Andy Gross <agross@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Rob Herring <robh+dt@kernel.org>, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/5] arm64: dts: qcom: sc7180: Start the trogdor
 eDP/touchscreen regulator on
Message-ID: <Y5J0YqLPtjIJ3Lpc@google.com>
References: <20221208192006.1070898-1-dianders@chromium.org>
 <20221208111910.3.I7050a61ba3a48e44b86053f265265b5e3c0cee31@changeid>
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On Thu, Dec 08, 2022 at 11:20:04AM -0800, Douglas Anderson wrote:
> Now that we've added the `off-on-delay-us` for the touchpanel
> regulator, we can see that we're actually hitting that delay at
> bootup. I saw about 200 ms of delay.
> 
> Let's avoid that delay by starting the regulator on. We'll only do
> this for eDP devices for the time being.
> 
> NOTE: we _won't_ do this for homestar. Homestar's panel really likes
> to be power cycled. It's why the Linux driver for this panel has a
> pm_runtime_put_sync_suspend() when the panel is being unprepared but
> the normal panel-edp driver doesn't. It's also why this hardware has a
> separate power rail for eDP vs. touchscreen, unlike all the other
> trogdor boards. We won't start homestar's regulator on. While this
> could mean a slight delay on homestar, it is probably a _correct_
> delay. The bootloader might have left the regulator on (it does so in
> dev and recovery modes), so if we turned the regulator off at probe
> time and we actually hit the delay then we were probably violating T12
> in the panel spec.
> 
> Signed-off-by: Douglas Anderson <dianders@chromium.org>

Reviewed-by: Matthias Kaehlcke <mka@chromium.org>