linux-kernel - Re: [PATCH 2/7] arm64: dts: qcom: sc7280: Add 3ms ramp to herobrine's pp3300_left_in

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Message-ID: <Y+KVUgRecTSPvdUs@google.com>
Date:   Tue, 7 Feb 2023 18:15:46 +0000
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Bjorn Andersson <andersson@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        linux-input@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        devicetree@...r.kernel.org, Stephen Kitt <steve@....org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Andy Gross <agross@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/7] arm64: dts: qcom: sc7280: Add 3ms ramp to
 herobrine's pp3300_left_in_mlb

On Mon, Feb 06, 2023 at 06:48:11PM -0800, Douglas Anderson wrote:
> The "pp3300_left_in_mlb" rail on herobrine eventually connects up to
> "vreg_edp_3p3" on the qcard. On several herobrine designs this rail
> has been measured to need more than 1ms to turn on.
> 
> While technically a herobrine derivative (defined as anyone including
> the "herobrine.dtsi") could change the board to make the rail rise
> faster or slower, the fact that two boards (evoker and villager) both
> measured it as taking more than 1ms implies that it's probably going
> to be the norm. Thus, let's add a "regulator-enable-ramp-delay"
> straight into the herobrine.dtsi to handle this. If a particular
> derivative board needs a faster or slower one then they can override
> it, though that feels unlikely.
> 
> While we measured something a bit over 1ms, we'll choose 3ms to give
> us a tiny bit of margin. This isn't a rail that turns off and on all
> the time anyway and 3ms is nothing compared to the total amount of
> time to power on a panel.
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>

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