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

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Date:   Thu, 21 Jul 2022 07:39:44 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     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>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.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 4:20 AM Mark Brown <broonie@...nel.org> wrote:
>
> On Thu, Jul 21, 2022 at 12:31:41PM +0200, Johan Hovold wrote:
>
> If you're copying someone into a thread that's not obviously relevant
> for them it's good practice to put a note about it at the top of the
> mail to reduce the chances that it just gets deleted unread - people get
> copies of all sorts of random stuff for not great reasons (like getting
> pulled in by checkpatch due to once having done a cleanup) and are often
> quicky to delete things.
>
> > 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.
>
> You could add a way to specify constant base loads in DT on either a per
> regulator or per consumer basis.

Yes, this please! ...on a per consumer basis. :-) It's been on my
wishlist for a while and would eliminate a massive amount of code /
tables in the drivers.

We could debate syntax, but I guess you'd either do it w/ two cells

vdda-phy-supply = <&vdda_mipi_dsi0_1p2 21800>;

...or with matching properties:

vdda-phy-supply = <&vdda_mipi_dsi0_1p2>;
vdda-phy-supply-base-load = <21800>;

-Doug