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From:   Doug Anderson <dianders@chromium.org>
Date:   Thu, 18 Aug 2022 15:39:43 -0700
Message-ID: <CAD=FV=UkaiDSYvm7W1tnoty=3dnYTUaEmNcbP7=uEzniELt7QA@mail.gmail.com>
Subject: Re: [PATCH] arm64: dts: qcom: sc7180: Add sleep state for alc5682 codec
To:     "Joseph S. Barrera III" <joebar@chromium.org>,
        Judy Hsiao <judyhsiao@chromium.org>
Cc:     Stephen Boyd <swboyd@chromium.org>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        Alexandru Stan <amstan@chromium.org>,
        Andy Gross <agross@kernel.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Konrad Dybcio <konrad.dybcio@somainline.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        Matthias Kaehlcke <mka@chromium.org>,
        Mengqi Guo <mqg@chromium.org>
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Hi,

On Thu, Aug 18, 2022 at 3:19 PM Joseph S. Barrera III
<joebar@chromium.org> wrote:
>
> On 8/18/22 1:34 PM, Doug Anderson wrote:
> > I tend to agree with Stephen's analysis. We actually need to keep the
> > pullup enabled unless we are actually turning power off to the codec,
> > which we don't seem to be doing.
> >
> > I guess I'm a little surprised that we don't even seem to turn any of
> > this codec's regulators off in S3. That seems like it would be drawing
> > power that we don't want. Maybe the "low power" mode of the codec is
> > low enough and we need to avoid powering it off to avoid pops / hisses
> > in S3 or something? If that's true, this might be one of those places
> > where the "LPM" of the regulators might actually be useful...
>
> OK, fair enough, so suggestions on what I should do instead? Should I
> look at why or how to turn the regulators off? Should I look into LPM?
> Are there existing bugs for such work?

It would be interesting to know from Judy if there's a reason we never
turn the audio codec rails off. Maybe there's history that I'm not
aware of? Matthias or Mengqi might also have ideas of how much power
is at stake here?

Ah, searching through the ChromeOS bug tracker finds some hits. At
this point we should probably move the discussion off the lists and
bring it back to the lists when we have some results. Unfortunately
most of the bugs are not public and so having a discussion here is
just noise for most people CCed.

-Doug