linux-kernel - Re: [PATCH RFC 1/2] regulator: core: Disable unused regulators with unknown status

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Date:   Fri, 6 Oct 2023 23:11:48 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Stephan Gerhold <stephan.gerhold@...nkonzept.com>,
        Mark Brown <broonie@...nel.org>
Cc:     Liam Girdwood <lgirdwood@...il.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        Stephan Gerhold <stephan@...hold.net>
Subject: Re: [PATCH RFC 1/2] regulator: core: Disable unused regulators with
 unknown status

On 4.10.2023 16:17, Stephan Gerhold wrote:
> Some regulator drivers do not provide a way to check if the regulator is
> currently enabled or not. That does not necessarily mean that the
> regulator is always-on. For example, the regulators managed by the RPM
> firmware on Qualcomm platforms can be either on or off during boot but
> the initial state is not known. To sync the state the regulator should
> get either explicitly enabled or explicitly disabled.
> 
> Enabling all regulators unconditionally is not safe, because we might
> not know which voltages are safe. The devices supplied by those
> regulators might also require a special power-up sequence where the
> regulators are turned on in a certain order or with specific delay.
> 
> Disabling all unused regulators is safer. If the regulator is already
> off it will just stay that way. If the regulator is on, disabling it
> explicitly allows the firmware to turn it off for reduced power
> consumption.
> 
> The regulator core already has functionality for disabling unused
> regulators. However, at the moment it assumes that all regulators where
> the .is_enabled() callback fails are actually off. There is no way to
> return a special value for the "unknown" state to explicitly ask for
> disabling those regulators.
> 
> Some drivers (e.g. qcom-rpmh-regulator.c) return -EINVAL for the case
> where the initial status is unknown. Use that return code to assume the
> initial status is unknown and try to explicitly disable the regulator
> in that case.
> 
> Signed-off-by: Stephan Gerhold <stephan.gerhold@...nkonzept.com>
> ---
> Instead of -EINVAL we could also use a different return code to indicate
> the initial status is unknown. Or maybe there is some other option that
> would be easier? This is working for me but I'm sending it as RFC to get
> more feedback. :)
-EOPNOTSUPP for "doesn't support getting is_enabled state"?

I think this looks really good.. And will definitely help finding
power hogs!

At the cost of breaking booting with broken DTs. But as the name by
which I referred to them suggests, this was never really destined to
work..

Konrad