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

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Message-ID: <Y/aeu5ua7cY5cGON@sirena.org.uk>
Date:   Wed, 22 Feb 2023 23:01:15 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.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 Wed, Feb 22, 2023 at 11:11:42PM +0100, Konrad Dybcio wrote:

> Thinking about it again, this seems like something that could be
> generalized and introduced into regulator core.. Hardcoding this
> will not end well.. Not to mention it'll affect all mp5496-using
> boards that are already upstream.

> WDYT about regulator-init-microvolts Mark?

The overwhelming majority of devices that have variable voltages
support readback, these Qualcomm firmware devices are pretty much
unique in this regard.  We don't want a general property to set a
specific voltage since normally we should be using the
constraints and don't normally need to adjust things immediately
since we can tell what the current voltage is. 

This is pretty much just going to be a device specific bodge,
ideally something that does know what the voltage is would be
able to tell us at runtime but if that's not possible then
there's no good options.  If the initial voltage might vary based
on board then a device specific DT property might be less
terrible, if it's determined by the regulator the current code
seems fine.  Or just leave the current behavour, if the
constraints are accurate then hopefully a temporary dip in
voltage is just inelegant rather than an issue.  Indeed the
current behaviour might well save power if you've got a voltage
range configured and nothing actually ever gets round to setting
the voltage (which is depressingly common, people seem keen on
setting voltage ranges even when the voltage is never varied in
practice).

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