linux-kernel - Re: [PATCH 7/8] arm64: dts: qcom: msm8939: Define regulator constraints next to usage

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Date:   Wed, 14 Jun 2023 13:51:08 +0100
From:   Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To:     Stephan Gerhold <stephan@...hold.net>,
        Bjorn Andersson <andersson@...nel.org>
Cc:     Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/8] arm64: dts: qcom: msm8939: Define regulator
 constraints next to usage

On 14/06/2023 08:16, Stephan Gerhold wrote:
> Right now each MSM8939 device has a huge block of regulator constraints
> with allowed voltages for each regulator. For lack of better
> documentation these voltages are often copied as-is from the vendor
> device tree, without much extra thought.
> 
> Unfortunately, the voltages in the vendor device trees are often
> misleading or even wrong, e.g. because:
> 
>   - There is a large voltage range allowed and the actual voltage is
>     only set somewhere hidden in some messy vendor driver. This is often
>     the case for pm8916_{l14,l15,l16} because they have a broad range of
>     1.8-3.3V by default.
> 
>   - The voltage is actually wrong but thanks to the voltage constraints
>     in the RPM firmware it still ends up applying the correct voltage.
> 
> To have proper regulator constraints it is important to review them in
> context of the usage. The current setup in the MSM8939 device trees
> makes this quite hard because each device duplicates the standard
> voltages for components of the SoC and mixes those with minor
> device-specific additions and dummy voltages for completely unused
> regulators.
> 
> The actual usage of the regulators for the SoC components is in
> msm8939-pm8916.dtsi, so it can and should also define the related
> voltage constraints. These are not board-specific but defined in the
> MSM8939/PM8916 specification. There is no documentation available for
> MSM8939 but in practice it's almost identical to MSM8916.
> 
> Note that this commit does not make any functional change. All used
> regulators still have the same regulator constraints as before. Unused
> regulators do not have regulator constraints anymore because most of
> these were too broad or even entirely wrong. They should be added back
> with proper voltage constraints when there is an actual usage.
> 
> The same changes were already made for MSM8916 in commit b0a8f16ae4a0
> ("arm64: dts: qcom: msm8916: Define regulator constraints next to usage").
> 
> Signed-off-by: Stephan Gerhold <stephan@...hold.net>


It makes sense to replicate the 8916 change.

Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@...aro.org>