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References: <20200428142629.8950-1-peron.clem@gmail.com> <98246e5d-ebef-bcb5-f0b8-d74b3834b835@arm.com>
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From:   =?UTF-8?B?Q2zDqW1lbnQgUMOpcm9u?= <peron.clem@gmail.com>
Date:   Tue, 28 Apr 2020 18:23:35 +0200
Message-ID: <CAJiuCcco0d_UoWeHqh6oc0rFNAMFynXjLRQ6APsT0WBh7m+GQg@mail.gmail.com>
Subject: Re: [linux-sunxi] Re: [PATCH v2] arm64: dts: allwinner: h6: Use dummy
 regulator for Tanix TX6
To:     Robin Murphy <robin.murphy@arm.com>
Cc:     Maxime Ripard <mripard@kernel.org>, Chen-Yu Tsai <wens@csie.org>,
        Rob Herring <robh+dt@kernel.org>,
        devicetree <devicetree@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-sunxi <linux-sunxi@googlegroups.com>,
        Piotr Oniszczuk <warpme@o2.pl>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
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Hi Robin,

On Tue, 28 Apr 2020 at 17:21, Robin Murphy <robin.murphy@arm.com> wrote:
>
> On 2020-04-28 3:26 pm, Cl=C3=A9ment P=C3=A9ron wrote:
> > Tanix TX6 has a fixed regulator. As DVFS is instructed to change
> > voltage to meet OPP table, the DVFS is not working as expected.
>
> Hmm, isn't that really a bug in the DVFS code? I guess it's just blindly
> propagating -EINVAL from the fixed regulators not implementing
> set_voltage, but AFAICS it has no real excuse not to be cleverer and
> still allow switching frequency as long as the voltage *is* high enough
> for the given OPP. I wonder how well it works if the regulator is
> programmable but shared with other consumers... that case probably can't
> be hacked around in DT.

Like you, I thought that the DVFS was clever enough to understand this
but guess not..

Maybe they are some cases where you don't want to leave the voltage high an=
d
reduce the frequency. But I don't know such case.

Regards,
Clement


>
> Robin.
>
> > Avoid to introduce a new dedicated OPP Table where voltage are
> > equals to the fixed regulator as it will only duplicate all the OPPs.
> > Instead remove the fixed regulator so the DVFS framework will create
> > dummy regulator and will have the same behavior.
> >
> > Add some comments to explain this in the device-tree.
> >
> > Reported-by: Piotr Oniszczuk <warpme@o2.pl>
> > Fixes: add1e27fb703 ("arm64: dts: allwinner: h6: Enable CPU opp tables =
for Tanix TX6")
> > Signed-off-by: Cl=C3=A9ment P=C3=A9ron <peron.clem@gmail.com>
> > ---
> >   .../boot/dts/allwinner/sun50i-h6-tanix-tx6.dts | 18 ++++++++++++++++-=
-
> >   1 file changed, 16 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/arm64/boot/dts/allwinner/sun50i-h6-tanix-tx6.dts b/ar=
ch/arm64/boot/dts/allwinner/sun50i-h6-tanix-tx6.dts
> > index be81330db14f..3e96fcb317ea 100644
> > --- a/arch/arm64/boot/dts/allwinner/sun50i-h6-tanix-tx6.dts
> > +++ b/arch/arm64/boot/dts/allwinner/sun50i-h6-tanix-tx6.dts
> > @@ -48,7 +48,15 @@
> >   };
> >
> >   &cpu0 {
> > -     cpu-supply =3D <&reg_vdd_cpu_gpu>;
> > +     /*
> > +      * Don't specify the CPU regulator, as it's a fixed
> > +      * regulator DVFS will not work as it is intructed
> > +      * to reach a voltage which can't be reached.
> > +      * Not specifying a regulator will create a dummy
> > +      * regulator allowing all OPPs.
> > +      *
> > +      * cpu-supply =3D <&reg_vdd_cpu_gpu>;
> > +      */
> >   };
> >
> >   &de {
> > @@ -68,7 +76,13 @@
> >   };
> >
> >   &gpu {
> > -     mali-supply =3D <&reg_vdd_cpu_gpu>;
> > +     /*
> > +      * Don't specify the GPU regulator, see comment
> > +      * above for the CPU supply.
> > +      *
> > +      * mali-supply =3D <&reg_vdd_cpu_gpu>;
> > +      */
> > +
> >       status =3D "okay";
> >   };
> >
> >
>
> --
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