linux-kernel - Re: [PATCH v5 10/10] arm64: dts: actions: Add uSD support for Cubieboard7

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Date:   Mon, 13 Jul 2020 08:30:56 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Amit Tomer <amittomer25@...il.com>
Cc:     Andre Przywara <andre.przywara@....com>,
        Andreas Färber <afaerber@...e.de>,
        Rob Herring <robh+dt@...nel.org>, cristian.ciocaltea@...il.com,
        linux-kernel@...r.kernel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-actions@...ts.infradead.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v5 10/10] arm64: dts: actions: Add uSD support for
 Cubieboard7

On Mon, Jul 13, 2020 at 12:15:28AM +0530, Amit Tomer wrote:
> Hi,
> 
> On Sun, Jul 12, 2020 at 11:00 PM Manivannan Sadhasivam
> <manivannan.sadhasivam@...aro.org> wrote:
> >
> > On Thu, Jul 02, 2020 at 08:22:56PM +0530, Amit Singh Tomar wrote:
> > > This commit adds uSD support for Cubieboard7 board based on Actions Semi
> > > S700 SoC. SD0 is connected to uSD slot. Since there is no PMIC support
> > > added yet, fixed regulator has been used as a regulator node.
> > >
> > > Signed-off-by: Amit Singh Tomar <amittomer25@...il.com>
> > > ---
> > > Changes since v4:
> > >       * No change.
> > > Changes since v3:
> > >         * No change.
> > > Changes since v2:
> > >         * No change.
> > > Changes since v1:
> > >         * No change.
> > > Changes since RFC:
> > >         * No change.
> > > ---
> > >  arch/arm64/boot/dts/actions/s700-cubieboard7.dts | 41 ++++++++++++++++++++++++
> > >  arch/arm64/boot/dts/actions/s700.dtsi            |  1 +
> > >  2 files changed, 42 insertions(+)
> > >
> > > diff --git a/arch/arm64/boot/dts/actions/s700-cubieboard7.dts b/arch/arm64/boot/dts/actions/s700-cubieboard7.dts
> > > index 63e375cd9eb4..ec117eb12f3a 100644
> > > --- a/arch/arm64/boot/dts/actions/s700-cubieboard7.dts
> > > +++ b/arch/arm64/boot/dts/actions/s700-cubieboard7.dts
> > > @@ -13,6 +13,7 @@
> > >
> > >       aliases {
> > >               serial3 = &uart3;
> > > +             mmc0 = &mmc0;
> > >       };
> > >
> > >       chosen {
> > > @@ -28,6 +29,23 @@
> > >               device_type = "memory";
> > >               reg = <0x1 0xe0000000 0x0 0x0>;
> > >       };
> > > +
> > > +     /* Fixed regulator used in the absence of PMIC */
> > > +     vcc_3v1: vcc-3v1 {
> > > +             compatible = "regulator-fixed";
> > > +             regulator-name = "fixed-3.1V";
> > > +             regulator-min-microvolt = <3100000>;
> > > +             regulator-max-microvolt = <3100000>;
> > > +     };
> >
> > Is this regulator used somewhere?
> 
> This is something I copied from bubblegum dts as I wasn't sure what is right way
> to include these regulators.
> 
> Also, another day tested it without having these regulators in , and
> still it seems to
> work.  So should these be removed ?
> 

Fixed regulators are used to nicely model the regulators which aren't tied to
any PMIC. But for some cases we use them to represent supplies when there is
no support for the specific PMIC present in the kernel and they are turned
on/configured by the bootloader (this is what happening here).

And there is no use of declaring fixed regulators when there is no consumer.
Even if you don't define these, the corresponding supplies in the board will
always be in the same state configured by the bootloader. So I'd suggest you
to remove this for now.

Since I don't have the schematics to check, please make sure you name the
regulators as mentioned in the schematics (this could vary from board to board,
so don't just copy from others).

Thanks,
Mani

> Thanks
> -Amit