linux-kernel - Re: [PATCH 3/9] arm64: dts: allwinner: pinebook: Remove unused AXP803 regulators

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Date:   Fri, 24 Jan 2020 17:33:18 +0100
From:   Maxime Ripard <maxime@...no.tech>
To:     Samuel Holland <samuel@...lland.org>
Cc:     Chen-Yu Tsai <wens@...e.org>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-sunxi@...glegroups.com
Subject: Re: [PATCH 3/9] arm64: dts: allwinner: pinebook: Remove unused
 AXP803 regulators

On Tue, Jan 21, 2020 at 09:14:02PM -0600, Samuel Holland wrote:
> On 1/21/20 3:05 AM, Maxime Ripard wrote:
> > On Sun, Jan 19, 2020 at 10:30:58AM -0600, Samuel Holland wrote:
> >> The Pinebook does not use the CSI bus on the A64. In fact it does not
> >> use GPIO port E for anything at all. Thus the following regulators are
> >> not used and do not need voltages set:
> >>
> >>  - ALDO1: Connected to VCC-PE only
> >>  - DLDO3: Not connected
> >>  - ELDO3: Not connected
> >>
> >> Signed-off-by: Samuel Holland <samuel@...lland.org>
> >> ---
> >>  .../boot/dts/allwinner/sun50i-a64-pinebook.dts   | 16 +---------------
> >>  1 file changed, 1 insertion(+), 15 deletions(-)
> >>
> >> diff --git a/arch/arm64/boot/dts/allwinner/sun50i-a64-pinebook.dts b/arch/arm64/boot/dts/allwinner/sun50i-a64-pinebook.dts
> >> index ff32ca1a495e..8e7ce6ad28dd 100644
> >> --- a/arch/arm64/boot/dts/allwinner/sun50i-a64-pinebook.dts
> >> +++ b/arch/arm64/boot/dts/allwinner/sun50i-a64-pinebook.dts
> >> @@ -202,9 +202,7 @@
> >>  };
> >>
> >>  &reg_aldo1 {
> >> -	regulator-min-microvolt = <2800000>;
> >> -	regulator-max-microvolt = <2800000>;
> >> -	regulator-name = "vcc-csi";
> >> +	regulator-name = "vcc-pe";
> >>  };
> >
> > If it's connected to PE, I'd expect the voltage to be at 3.3v?
>
> If we provide voltage constraints, the regulator core will enable the regulator
> and set its voltage at boot. That seems like a bit of a waste.

I'm not sure the regulator core enables them if there's neither
regulator-boot-on nor regulator-always-on.

> I don't think the voltage really matters, since nothing is plugged in to the
> port. ALDO1 can't go over 3.3V anyway, so even if it does get turned on for some
> reason, nothing will get damaged.

Looking at the schematics, it looks like the PE pins are connected to
the front-facing camera?

Maxime