linux-kernel - Re: [PATCH] arm64: dts: sc7180: Fix ps8640 power sequence for Homestar rev4

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Date:   Mon, 15 Nov 2021 07:40:15 -0800
From:   Doug Anderson <dianders@...omium.org>
To:     yangcong <yangcong5@...qin.corp-partner.google.com>
Cc:     philipchen@...omium.org, agross@...nel.org,
        bjorn.andersson@...aro.org, robh+dt@...nel.org,
        swboyd@...omium.org, devicetree@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: sc7180: Fix ps8640 power sequence for
 Homestar rev4

Hi,

On Sun, Nov 14, 2021 at 7:02 PM yangcong
<yangcong5@...qin.corp-partner.google.com> wrote:
>
> When powering up the ps8640, we need to deassert PD right
> after we turn on the vdd33 regulator. Unfortunately, the vdd33
> regulator takes some time (~4ms) to turn on. Add in the delay
> for the vdd33 regulator so that when the driver deasserts PD
> that the regulator has had time to ramp.
>
> Signed-off-by: yangcong <yangcong5@...qin.corp-partner.google.com>
> ---
>  arch/arm64/boot/dts/qcom/sc7180-trogdor-homestar-r4.dts | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/arch/arm64/boot/dts/qcom/sc7180-trogdor-homestar-r4.dts b/arch/arm64/boot/dts/qcom/sc7180-trogdor-homestar-r4.dts
> index fb27106bbb4a..0de0c97f5728 100644
> --- a/arch/arm64/boot/dts/qcom/sc7180-trogdor-homestar-r4.dts
> +++ b/arch/arm64/boot/dts/qcom/sc7180-trogdor-homestar-r4.dts
> @@ -15,3 +15,7 @@ / {
>         model = "Google Homestar (rev4+)";
>         compatible = "google,homestar", "qcom,sc7180";
>  };
> +
> +&pp3300_brij_ps8640 {
> +       regulator-enable-ramp-delay = <4000>;
> +};

It should have been pointed out somewhere in the post, but this patch
depends on Philip's most recent, which is:

https://lore.kernel.org/r/20211029152647.v3.4.If7aaa8e36f1269acae5488035bd62ce543756bf8@changeid/

This seems fine to me. Apparently this 4ms delay isn't needed
lazor-rev9 (at least they were happy with the signals on that board)
which is why this is a homestar change. That can make sense since the
components on the two boards may be different.

In any case:

Reviewed-by: Douglas Anderson <dianders@...omium.org>