linux-kernel - Re: [PATCH v2 02/13] dt-bindings: pinctrl: renesas: Document RZ/V2H(P) SoC

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Message-ID: <CA+V-a8t=fAmMRsxwkXX7KBV=jdSVZ-twpN-yQp1Eb7M+X5T-ng@mail.gmail.com>
Date: Thu, 25 Apr 2024 10:49:26 +0100
From: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Linus Walleij <linus.walleij@...aro.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Magnus Damm <magnus.damm@...il.com>, linux-renesas-soc@...r.kernel.org, 
	linux-gpio@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Biju Das <biju.das.jz@...renesas.com>, 
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>, 
	Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH v2 02/13] dt-bindings: pinctrl: renesas: Document
 RZ/V2H(P) SoC

Hi Geert,

Thank you for the review.

On Wed, Apr 24, 2024 at 10:06 AM Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
>
> Hi Prabhakar,
>
> Thanks for your patch!
>
> On Tue, Apr 23, 2024 at 7:59 PM Prabhakar <prabhakar.csengg@...ilcom> wrote:
> > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> >
> > Add documentation for the pin controller found on the Renesas RZ/V2H(P)
> > (R9A09G057) SoC. The RZ/V2H PFC varies slightly compared to the RZ/G2L
> > family:
> > - Additional bits need to be set during pinmuxing.
> > - The GPIO pin count is different.
> >
> > Hence, a SoC-specific compatible string, 'renesas,r9a09g057-pinctrl', is
> > added for the RZ/V2H(P) SoC.
> >
> > Also, add the 'renesas,output-impedance' property. The drive strength
> > setting on RZ/V2H(P) depends on the different power rails coming out from
> > the PMIC (connected via I2C). These power rails (required for drive
> > strength) can be 1.2V, 1.8V, or 3.3V.
> >
> > Pins are grouped into 4 groups:
> >
> > Group 1: Impedance
> > - 150/75/38/25 ohms (at 3.3V)
> > - 130/65/33/22 ohms (at 1.8V)
> >
> > Group 2: Impedance
> > - 50/40/33/25 ohms (at 1.8V)
> >
> > Group 3: Impedance
> > - 150/75/37.5/25 ohms (at 3.3V)
> > - 130/65/33/22 ohms (at 1.8V)
> >
> > Group 4: Impedance
> > - 110/55/30/20 ohms (at 1.8V)
> > - 150/75/38/25 ohms (at 1.2V)
> >
> > The 'renesas,output-impedance' property, as documented, can be
> > [0, 1, 2, 3], indicating x1/x2/x3/x4 drive strength.
>
> The documentation says "x1/x2/x4/x6" for all but Group 4 (P20/P21).
> Still, the actual values don't seem to match the magnification factors...
>
> > As power rail information may not be available very early in the boot
> > process, the 'renesas,output-impedance' property is added instead of
> > reusing the 'output-impedance-ohms' property.
> >
> > Also, allow bias-disable, bias-pull-down and bias-pull-up properties
> > as these can be used to configure the pins.
> >
> > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
>
> > --- a/Documentation/devicetree/bindings/pinctrl/renesas,rzg2l-pinctrl.yaml
> > +++ b/Documentation/devicetree/bindings/pinctrl/renesas,rzg2l-pinctrl.yaml
> > @@ -111,6 +116,18 @@ additionalProperties:
> >          output-high: true
> >          output-low: true
> >          line-name: true
> > +        bias-disable: true
> > +        bias-pull-down: true
> > +        bias-pull-up: true
> > +        renesas,output-impedance:
> > +          description: |
> > +            Output impedance for pins on RZ/V2H(P) SoC.
> > +            0: Corresponds to x1
> > +            1: Corresponds to x2
> > +            2: Corresponds to x3
> > +            3: Corresponds to x4
>
> Hence I'd drop the multiplication factors, and just say the meaning
> of the value is pin-dependent?
>
Agreed, I will update the description "Output impedance for pins on
RZ/V2H(P) SoC. 0/1/2/3 corresponds to register bit values that can be
set in PFC_IOLH_mn register which adjusts the drive strength value and
is pin-dependent"

Cheers,
Prabhakar

> > +          $ref: /schemas/types.yaml#/definitions/uint32
> > +          enum: [0, 1, 2, 3]
> >
> >      - type: object
> >        additionalProperties:
>
> 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