Re: [PATCH 1/4] arm64: dts: mediatek: mt8183-kukui-jacuzzi: Drop pp3300_panel voltage settings

[AngeloGioacchino Del Regno]

Il 04/11/24 14:00, Chen-Yu Tsai ha scritto:
> On Wed, Oct 30, 2024 at 3:02 PM Chen-Yu Tsai <wenst@xxxxxxxxxxxx> wrote:
> > The pp3300_panel fixed regulator is just a load switch. It does not have
> > any regulating capabilities. Thus having voltage constraints on it is
> > wrong.
> >
> > Remove the voltage constraints.
> >
> > Fixes: cabc71b08eb5 ("arm64: dts: mt8183: Add kukui-jacuzzi-damu board")
> > Signed-off-by: Chen-Yu Tsai <wenst@xxxxxxxxxxxx>
>
> I see that the other three patches were merged and included in the pull
> request, but not this one. Were there any concerns?

Sorry I forgot to actually provide an explanation for that - yes, I do have some
comment about this one.

Despite this being a load switch, it's still switching power from regulator A to
target device X, so this is technically still providing 3.3V to device X.

Think about how a "regular" full-fledged regulator works: you can (sometimes) set
a voltage, and then you can ENABLE the VOUT for said regulator (/rail): this kind
of "load switch" does exactly the same as the ENABLE switch for a full-fledged
regulator.

So, this is switching on and off a power rail that is derived from a source rail,
practically creating... well, a "new" rail, with...

 VIN=somewhere-3.3v,
 VOUT=somewhere-still-3.3v

Any objections/doubts/etc? :-)

P.S.: I'm writing fast, sorry if anything appears unclear, feel free to shoot more
      questions in case :-)

Cheers,
Angelo

> ChenYu
>
> > ---
> >   arch/arm64/boot/dts/mediatek/mt8183-kukui-jacuzzi.dtsi | 2 --
> >   1 file changed, 2 deletions(-)
> >
> > diff --git a/arch/arm64/boot/dts/mediatek/mt8183-kukui-jacuzzi.dtsi b/arch/arm64/boot/dts/mediatek/mt8183-kukui-jacuzzi.dtsi
> > index 783c333107bc..7bbafe926558 100644
> > --- a/arch/arm64/boot/dts/mediatek/mt8183-kukui-jacuzzi.dtsi
> > +++ b/arch/arm64/boot/dts/mediatek/mt8183-kukui-jacuzzi.dtsi
> > @@ -35,8 +35,6 @@ pp1800_mipibrdg: pp1800-mipibrdg {
> >          pp3300_panel: pp3300-panel {
> >                  compatible = "regulator-fixed";
> >                  regulator-name = "pp3300_panel";
> > -               regulator-min-microvolt = <3300000>;
> > -               regulator-max-microvolt = <3300000>;
> >                  pinctrl-names = "default";
> >                  pinctrl-0 = <&pp3300_panel_pins>;
> >
> > --
> > 2.47.0.163.g1226f6d8fa-goog