linux-kernel - Re: [RFC PATCH v2 09/17] ARM: dts: tegra20: harmony: Setup voltage regulators for DVFS

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Date:   Mon, 22 Oct 2018 09:33:23 -0600
From:   Stephen Warren <swarren@...dotorg.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Nishanth Menon <nm@...com>, Stephen Boyd <sboyd@...nel.org>,
        Marcel Ziswiler <marcel.ziswiler@...adex.com>,
        linux-tegra@...r.kernel.org, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 09/17] ARM: dts: tegra20: harmony: Setup voltage
 regulators for DVFS

On 10/21/18 2:54 PM, Dmitry Osipenko wrote:
> Set min/max regulators voltage and add CPU node that hooks up CPU with
> voltage regulators.

> diff --git a/arch/arm/boot/dts/tegra20-harmony.dts b/arch/arm/boot/dts/tegra20-harmony.dts

> -				sm0 {
> +				core_vdd_reg: sm0 {
>   					regulator-name = "vdd_sm0,vdd_core";
> -					regulator-min-microvolt = <1200000>;
> -					regulator-max-microvolt = <1200000>;
> +					regulator-min-microvolt = <1000000>;
> +					regulator-max-microvolt = <1300000>;
> +					regulator-coupled-with = <&rtc_vdd_reg>;
> +					regulator-coupled-max-spread = <150000>;
>   					regulator-always-on;
>   				};

How do you know for sure that these increased ranges are safe (high end) 
and stable (low end) for this particular board? IIRC the safe/legal 
range depends on the chip SKU, and to be honest I have no idea which SKU 
is present on Harmony... For public boards like Colibri I imagine 
there's enough information out there to tell what will work, but maybe 
not our internal boards like Harmony, unless you checked our ancient 
downstream kernels?