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

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Message-ID: <CAA8EJprQnnWjDZJy9+zUBsVQCi3jtc0Ngtzzk9MXpwOvuAS68g@mail.gmail.com>
Date:   Thu, 21 Jul 2022 16:25:32 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Kuogee Hsieh <quic_khsieh@...cinc.com>,
        Douglas Anderson <dianders@...omium.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Vinod Koul <vkoul@...nel.org>, Mark Brown <broonie@...nel.org>,
        dri-devel@...ts.freedesktop.org, robdclark@...il.com,
        sean@...rly.run, swboyd@...omium.org, daniel@...ll.ch,
        airlied@...ux.ie, agross@...nel.org, quic_abhinavk@...cinc.com,
        quic_aravindh@...cinc.com, quic_sbillaka@...cinc.com,
        freedreno@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        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

On Thu, 21 Jul 2022 at 13:31, Johan Hovold <johan@...nel.org> wrote:
>
> On Tue, Jul 05, 2022 at 09:29:13AM -0700, Kuogee Hsieh wrote:
> > 0) rebase on https://git.kernel.org/pub/scm/linux/kernel/git/phy/linux-phy.git tree
> > 1) add regulator_set_load() to eDP phy
> > 2) add regulator_set_load() to DP phy
> > 3) remove vdda related function out of eDP/DP controller
> >
> > Kuogee Hsieh (3):
> >   phy: qcom-edp: add regulator_set_load to edp phy
> >   phy: qcom-qmp: add regulator_set_load to dp phy
> >   drm/msm/dp: delete vdda regulator related functions from eDP/DP
> >     controller
> >
> >  drivers/gpu/drm/msm/dp/dp_parser.c        | 14 -----
> >  drivers/gpu/drm/msm/dp/dp_parser.h        |  8 ---
> >  drivers/gpu/drm/msm/dp/dp_power.c         | 95 +------------------------------
> >  drivers/phy/qualcomm/phy-qcom-edp.c       | 12 ++++
> >  drivers/phy/qualcomm/phy-qcom-qmp-combo.c | 41 ++++++++++---
> >  5 files changed, 46 insertions(+), 124 deletions(-)
>
> This series breaks USB and PCIe for some SC8280XP and SA540P machines
> where the DP PHY regulators are shared with other PHYs whose drivers do
> not request a load.

I'm trying to understand, why does this series cause the regression.
Previously it would be the DP controller voting on the regulators
load, now it has been moved to the DP/eDP PHYs.

> Specifically, the hard-coded vdda-phy load of 21.8 mA added by this
> series, causes several RPMh regulators to now be put in low-power mode.
>
> I found Doug's suggestion to handle situations like this in regulator
> core:
>
>         https://lore.kernel.org/all/20180814170617.100087-1-dianders@chromium.org/
>
> but since that was rejected, how do we deal with this generally?
>
> In the above thread Doug mentioned adding support for load requests to
> further drivers and Bjorn mentioned working around it by adding
> regulator-system-load properties to DT.
>
> It seems quite likely that changes like this one affects other systems
> too, and the effects may be hard to debug. So a more general solution
> than playing whack-a-mole using DT would be good to have.

I think enabling a regulator which supports set_load() and without
load being set should cause a warning, at least with
CONFIG_REGULATOR_DEBUG. WDYT?

-- 
With best wishes
Dmitry