linux-kernel - Re: [PATCH V2 4/6] regulator: qcom_smd: Add support to define the bootup voltage

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Date:   Mon, 3 Apr 2023 20:21:25 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     Devi Priya <quic_devipriy@...cinc.com>, agross@...nel.org,
        andersson@...nel.org, lgirdwood@...il.com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        quic_srichara@...cinc.com, quic_gokulsri@...cinc.com,
        quic_sjaganat@...cinc.com, quic_kathirav@...cinc.com,
        quic_arajkuma@...cinc.com, quic_anusha@...cinc.com,
        quic_ipkumar@...cinc.com
Subject: Re: [PATCH V2 4/6] regulator: qcom_smd: Add support to define the
 bootup voltage



On 3.04.2023 20:14, Mark Brown wrote:
> On Mon, Apr 03, 2023 at 07:53:48PM +0200, Konrad Dybcio wrote:
>> On 3.04.2023 16:07, Devi Priya wrote:
> 
>>> But, when the regulator driver comes up, it tries to bring up the
>>> regulators to the minimum supported voltage provided with the
>>> regulator-min-microvolt property in the DT.
> 
>> Right, that exists.. 
> 
>> Mark, do you think it should be updated such that the requests are
>> aggregated before assuming min_uV is "just fine"?
> 
> We can't tell if any consumers are ever going to appear, and the
> regulator having a voltage outside of the constraints is an urgent
> problem we need to fix quickly.  Since we try to bring the voltage to
> the nearest end of the constraint the driver could always change the
> bogus voltage it reports to one that is excessively high, this would
> mean the core will try to bring the voltage down to the maximum rather
> than up to the minimum.  The driver could also look at the constraints
> when guessing at the hardware configuration rather than claiming an out
> of spec voltage, this would mean we wouldn't need to correct anything.
Hm, all of what you said sounds like a valid concern.. And then we
probably shouldn't shoot up to max by default, as going too low is
not going to cause as much potential irreversible damage as going
too high.. Especially with programmer error..

Too bad Qualcomm's firmware architecture doesn't allow for reading
back the voltage..

Konrad