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

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Date:   Thu, 21 Jul 2022 12:31:41 +0200
From:   Johan Hovold <johan@...nel.org>
To:     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>
Cc:     dri-devel@...ts.freedesktop.org, robdclark@...il.com,
        sean@...rly.run, swboyd@...omium.org, daniel@...ll.ch,
        airlied@...ux.ie, agross@...nel.org, dmitry.baryshkov@...aro.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 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.

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.

Johan