linux-kernel - Re: [PATCH v2] arm64: dts: renesas: r9a09g057: Add OPP table

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Message-ID: <CAMuHMdULuCWd1V0Az=NWHhSb7voDKbTo9rp3Excntp7qvTbbuQ@mail.gmail.com>
Date: Wed, 9 Oct 2024 11:28:04 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc: Biju Das <biju.das.jz@...renesas.com>, Magnus Damm <magnus.damm@...il.com>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>, 
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>, 
	Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH v2] arm64: dts: renesas: r9a09g057: Add OPP table

Hi Prabhakar,

On Tue, Oct 8, 2024 at 10:10 PM Lad, Prabhakar
<prabhakar.csengg@...il.com> wrote:
> On Tue, Oct 8, 2024 at 6:33 PM Biju Das <biju.das.jz@...renesas.com> wrote:
> > > From: Biju Das <biju.das.jz@...renesas.com>
> > > > From: Prabhakar <prabhakar.csengg@...il.com>
> > > > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > > >
> > > > Add OPP table for RZ/V2H(P) SoC.
> > > >
> > > > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > > > ---
> > > > v1->v2
> > > > - Set opp-microvolt to 800000 for frequencies below 1.1GHz
> > > > ---
> > > >  arch/arm64/boot/dts/renesas/r9a09g057.dtsi | 41 ++++++++++++++++++++++
> > > >  1 file changed, 41 insertions(+)
> > > >
> > > > diff --git a/arch/arm64/boot/dts/renesas/r9a09g057.dtsi b/arch/arm64/boot/dts/renesas/r9a09g057.dtsi
> > > > index 1ad5a1b6917f..4bbe75b81f54 100644
> > > > --- a/arch/arm64/boot/dts/renesas/r9a09g057.dtsi
> > > > +++ b/arch/arm64/boot/dts/renesas/r9a09g057.dtsi
> > > > @@ -20,6 +20,39 @@ audio_extal_clk: audio-clk {
> > > >             clock-frequency = <0>;
> > > >     };
> > > >
> > > > +   /*
> > > > +    * The default cluster table is based on the assumption that the PLLCA55 clock
> > > > +    * frequency is set to 1.7GHz. The PLLCA55 clock frequency can be set to
> > > > +    * 1.7/1.6/1.5/1.1 GHz based on the BOOTPLLCA_0/1 pins (and additionally can be
> > > > +    * clocked to 1.8GHz as well). The table below should be overridden in the board
> > > > +    * DTS based on the PLLCA55 clock frequency.
> > > > +    */
> > > > +   cluster0_opp: opp-table-0 {
> > > > +           compatible = "operating-points-v2";
> > > > +
> > > > +           opp-1700000000 {
> > > > +                   opp-hz = /bits/ 64 <1700000000>;
> > > > +                   opp-microvolt = <900000>;
> > >
> > > Not sure CA-55 can change voltage from 800mV to 900mV??
> > > Based on Power Domain Control, it needs to be in AWO mode for changing the PD_CA55 voltage.
> > >
> > > The manual says OD voltage is 0.9V and ND voltage is 0.8V.
> > >
> > > Is 1.7GHZ is ND or OD?
> >
> > {1.7,1.6,1.5 GHz} is enabled when VDD09_CA55 is at 0.9 V
> > and for 1.1 GHz it is 0.8V.
> >
> > Maybe when you do /2, /4, /8 using dividers, the voltage may be still
> > the same??
> >
> I think you are right when BOOTPLLCA[1:0] pins are set to 1.7GHz the
> VDD09_CA55 is at 0.9 V, further dividing the clock shouldnt affect the
> voltage levels at the PMIC output.
>
> Geert, please let me know if my understanding is incorrect.

The actual VDD09_CA55 voltage is controlled by the external PMIC
(RAA215300).  It is the responsibility of the system designer to make
sure VDD09_CA55 is at 0.9V when BOOTPLLCA[1:0] is strapped for OD,
as CPU core clock rates higher than 1.1 GHz need a higher core voltage.
I don't think it hurts to supply the higher core voltage while
running the CPU core at low core frequencies, except for extra power
consumption.

To control VDD09_CA55 dynamically, the CPU cores should have cpu-supply
properties pointing to the regulator controlling it (raa215300).
I haven't checked how Linux behaves when no cpu-supply property is
present, or when it points to a fixed regulator.

I am also wondering if other opps (1.1/1.5/1.6/1.8 GHz) should be
added, too?  And probably any opp above 1.1GHz opp should be tagged with
"turbo-mode"?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds