Re: [PATCH] arm64: dts: renesas: rzt2h-n2h-evk: Add VCC supply for EEPROM

[Geert Uytterhoeven]

Hi Prabhakar,

CC at24, regulator

On Tue, 14 Oct 2025 at 17:33, Prabhakar <prabhakar.csengg@xxxxxxxxx> wrote:
> From: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
> The R1EX24016 EEPROM on the RZ/T2H-N2H Evaluation Kit is powered from
> the 3.3V rail. Add the regulator phandle for the VCC supply to reflect
> this in the device tree and avoid the fallback to the dummy regulator:
>
>     at24 0-0050: supply vcc not found, using dummy regulator
>
> Fixes: 0176c9e82e10 ("arm64: dts: renesas: rzt2h-n2h-evk-common: Enable EEPROM on I2C0")
> Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>

Thanks for your patch!

> --- a/arch/arm64/boot/dts/renesas/rzt2h-n2h-evk-common.dtsi
> +++ b/arch/arm64/boot/dts/renesas/rzt2h-n2h-evk-common.dtsi
> @@ -160,6 +160,7 @@ eeprom: eeprom@50 {
>                 compatible = "renesas,r1ex24016", "atmel,24c16";
>                 reg = <0x50>;
>                 pagesize = <16>;
> +               vcc-supply = <&reg_3p3v>;
>         };
>  };

"vcc-supply" is not a required property, according to the DT bindings,
and I believe the 3.3V supply can be considered always-on (but see
below to encounter dragons).
I was always under the impression that these "supply not found, using
dummy regulator"-messages are just informational, and can be ignored,
but they are at the KERN_WARNING level.
So should we add real dummy supplies to DTS, or not?

Thanks!

P.S. Actually the 3.3V supply is controlled by an SLG7RN46899, which is
     an "RZ/T2H Power Sequencer with IIC".  From a quick glance at the
     documentation, it is not clear to me what is the purpose of the
     I2C interface, and whether it can be used to control the outputs
     or not.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

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