linux-kernel - Re: [PATCH 09/14] regulator: dts: add full voltage range to LDO4 on the Lime2

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Date:   Mon, 26 Nov 2018 16:57:38 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Priit Laes <plaes@...es.org>
Cc:     Lee Jones <lee.jones@...aro.org>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Chen-Yu Tsai <wens@...e.org>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sebastian Reichel <sre@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org,
        Olliver Schinagl <oliver@...inagl.nl>
Subject: Re: [PATCH 09/14] regulator: dts: add full voltage range to LDO4 on
 the Lime2

On Mon, Nov 26, 2018 at 05:27:50PM +0200, Priit Laes wrote:

> In the defense of LDO3, LDO3 is the regulator that feeds port bank E,
> which has no other purpose then a CSI/TS interface, however the case
> may still be, that the connected IO may be just as well be 3.3 volts.
> The big misnomer is however, that the schematic names GPIO-2 pin4
> LDO3_2.8V, rather then VDD-CSI0 or similar.

In general you want to run regulators at the lowest voltage you can,
this tends to reduce power consumption.

> Ideally, we want to set a supply voltage for each port bank, but the
> monolithic nature of the sunxi pinctroller currently prevents this and
> as such, the board should at least configure the LDO4 with the proper
> ranges.

>  &reg_ldo4 {
> -	regulator-min-microvolt = <2800000>;
> -	regulator-max-microvolt = <2800000>;
> -	regulator-name = "vddio-csi1";
> +	regulator-always-on;
> +	regulator-min-microvolt = <1250000>;
> +	regulator-max-microvolt = <3300000>;
> +	regulator-name = "vdd-io-pg";
>  };

This is obviously broken even according to your analysis above - if you
have consumers for which 2.8V is too low allowing other consumers to set
even lower voltages is not going to help as soon as they start doing
that.

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