linux-kernel - Re: [PATCH] arm64: dts: qcom: msm8916/39-samsung-a2015: Add PMIC and charger

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Date:   Tue, 5 Dec 2023 12:30:50 +0100
From:   Stephan Gerhold <stephan@...hold.net>
To:     Bryan O'Donoghue <bryan.odonoghue@...aro.org>
Cc:     Raymond Hackley <raymondhackley@...tonmail.com>,
        linux-kernel@...r.kernel.org, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Jakob Hauser <jahau@...ketmail.com>,
        Nikita Travkin <nikita@...n.ru>, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, ~postmarketos/upstreaming@...ts.sr.ht
Subject: Re: [PATCH] arm64: dts: qcom: msm8916/39-samsung-a2015: Add PMIC and
 charger

On Tue, Dec 05, 2023 at 12:17:15PM +0100, Bryan O'Donoghue wrote:
> On 05/12/2023 10:38, Raymond Hackley wrote:
> > The phones listed below have Richtek RT5033 PMIC and charger.
> > Add them to the device trees.
> > 
> > - Samsung Galaxy A3/A5/A7 2015
> > - Samsung Galaxy E5/E7
> > - Samsung Galaxy Grand Max
> > 
> > Signed-off-by: Raymond Hackley <raymondhackley@...tonmail.com>
> > [...]
> > +			/*
> > +			 * Needed for camera, but not used yet.
> > +			 * Define empty nodes to allow disabling the unused
> > +			 * regulators.
> > +			 */
> > +			LDO {};
> > +			BUCK {};
> > +		};
> 
> Aren't the camera regulators off until enabled ?
> 

We don't know for sure what state they are in during boot. If we omit
these nodes the regulator core will ignore these regulators completely
and just leave them in whatever state they are.

I would indeed expect them to be off after reset, but there are also
other situations in which Linux might be booted, such as kexec. That's
why it's usually better to be explicit and avoid relying on boot/reset
states altogether.

Thanks,
Stephan