linux-kernel - Re: [PATCH 3/5] arm64: dts: qcom: sc7180: Start the trogdor eDP/touchscreen regulator on

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Date:   Thu, 8 Dec 2022 23:33:54 +0000
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Bjorn Andersson <andersson@...nel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        swboyd@...omium.org, linux-arm-msm@...r.kernel.org,
        linux-input@...r.kernel.org,
        Yunlong Jia <ecs.beijing2022@...il.com>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] arm64: dts: qcom: sc7180: Start the trogdor
 eDP/touchscreen regulator on

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@...omium.org>

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