linux-kernel - Re: [PATCH v3 1/2] regulator: dt-bindings: add QCOM RPMh regulator bindings

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Message-ID: <CAD=FV=UpWEMSPUYOHmLQ0g_mF990kwn4_zm=ZCNttLKZiz7i=Q@mail.gmail.com>
Date:   Wed, 30 May 2018 09:31:55 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     David Collins <collinsd@...eaurora.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-msm@...r.kernel.org,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        devicetree@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Stephen Boyd <sboyd@...nel.org>
Subject: Re: [PATCH v3 1/2] regulator: dt-bindings: add QCOM RPMh regulator bindings

Hi,

On Wed, May 30, 2018 at 9:13 AM, Mark Brown <broonie@...nel.org> wrote:
> On Wed, May 30, 2018 at 09:09:02AM -0700, Doug Anderson wrote:
>> On Wed, May 30, 2018 at 9:07 AM, Mark Brown <broonie@...nel.org> wrote:
>
>> > It needs something to tell it what the new voltage to set is.
>
>> The regulator driver has its own cache of what voltage was most
>> recently requested by Linux.  It can use that, can't it?
>
> If we're just going to use the most recently set voltage then hopefully
> the hardware already knew that, and it might not be the lowest available
> voltage if the last consumer to get turned off was holding the voltage
> higher.

To circle back to the original point: the problem is that (IMHO) the
hardware is doing the wrong thing by still counting Linux's vote for a
voltage even though Linux also voted that the regulator should be
disabled.  So basically we're working around the hardware by
pretending to vote for a dummy lower voltage whenever Linux wants the
regulator disabled.  From Linux's point of view everything works as
normal--we just tell the hardware a falsehood so it doesn't count our
vote for a voltage while the regulator is disabled.

-Doug