linux-kernel - Re: [PATCH v16 0/3] eDP/DP Phy vdda realted function

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Message-ID: <CAD=FV=XDOxy1R5ipD0errwi6GOFz-X6G3_WE34LGLqmWE6_iyw@mail.gmail.com>
Date:   Thu, 21 Jul 2022 08:43:48 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Johan Hovold <johan@...nel.org>,
        Kuogee Hsieh <quic_khsieh@...cinc.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Vinod Koul <vkoul@...nel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Stephen Boyd <swboyd@...omium.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Andy Gross <agross@...nel.org>,
        "Abhinav Kumar (QUIC)" <quic_abhinavk@...cinc.com>,
        "Aravind Venkateswaran (QUIC)" <quic_aravindh@...cinc.com>,
        Sankeerth Billakanti <quic_sbillaka@...cinc.com>,
        freedreno <freedreno@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Subject: Re: [PATCH v16 0/3] eDP/DP Phy vdda realted function

Hi,

On Thu, Jul 21, 2022 at 8:06 AM Mark Brown <broonie@...nel.org> wrote:
>
> On Thu, Jul 21, 2022 at 07:49:55AM -0700, Doug Anderson wrote:
>
> > Every single LDO on Qualcomm's PMICs seems to be able to be set in
> > "high power mode" and "low power mode", but I think the majority of
> > clients only really care about two things: on and in high power mode
> > vs. off. I think the amount of stuff peripherals can do in low power
> > mode is super limited, so you have to be _really_ sure that the
> > peripheral won't draw too much current without you having a chance to
> > reconfigure the regulator.
>
> *Generally* a low power mode would be mainly useful for low power
> retention type states, not active use.

Right. Certainly the case I've seen where it is most useful is in S3
where we need to keep a device powered just enough to detect a wakeup,
but it can definitely also be useful for mostly idle devices that we
need to keep powered to retain memory so they can start up again
quickly.

I guess I'd put it this way, though: how many drivers in Linux today
have _two_ calls to regulator_set_load(): one for the "active" state
and one for the retention state. Looks like UFS maybe. Any others? For
most devices the pattern is:

* get all of our regulators.
* for each regulator, set the load to something that will trigger HPM
when we're using the regulator.
* turn regulators on when we need power and off when we don't.

All the extra scaffolding and tables to pass something to
regulator_set_load() is just a lot of noise to add for drivers that
don't have any concept of "retention" mode and don't need it.

-Doug