linux-kernel - Re: [PATCH 1/2] dt-bindings: power: Add regulator-pd yaml file

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Message-ID: <PAXPR04MB9185D87525AA88A8C3543EEA89E0A@PAXPR04MB9185.eurprd04.prod.outlook.com>
Date:   Mon, 28 Aug 2023 19:09:36 +0000
From:   Shenwei Wang <shenwei.wang@....com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Ulf Hansson <ulf.hansson@...aro.org>
CC:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        "imx@...ts.linux.dev" <imx@...ts.linux.dev>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH 1/2] dt-bindings: power: Add regulator-pd yaml file



> -----Original Message-----
> From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
> Sent: Monday, August 28, 2023 1:53 PM
> To: Shenwei Wang <shenwei.wang@....com>; Ulf Hansson
> <ulf.hansson@...aro.org>
> Cc: Rob Herring <robh+dt@...nel.org>; Krzysztof Kozlowski
> <krzysztof.kozlowski+dt@...aro.org>; Conor Dooley <conor+dt@...nel.org>;
> Liam Girdwood <lgirdwood@...il.com>; Mark Brown <broonie@...nel.org>;
> imx@...ts.linux.dev; devicetree@...r.kernel.org; linux-kernel@...r.kernel.org;
> dl-linux-imx <linux-imx@....com>
> Subject: [EXT] Re: [PATCH 1/2] dt-bindings: power: Add regulator-pd yaml file
> >>>>>>> Are you suggesting to move the regulator-pd to the imx directory
> >>>>>>> and add a company prefix to the compatible string?
> >>>>>>
> >>>>>> There is no such part of iMX processor as such
> >>>>>> regulator-power-domain, so I don't recommend that approach. DTS
> >>>>>> nodes represent hardware, not your SW layers.
> >>>>>>
> >>>>>
> >>>>> That's not always the case, as we do sometimes need a virtual device.
> >>>>> As an example, the "regulator-fixed" acts as a software
> >>>>> abstraction layer to create virtual regulator devices by
> >>>>> interfacing with the underlying
> >>>> GPIO drivers.
> >>>>
> >>>> Not true. This is a real regulator device. Real hardware on the board.
> >>>> You can even see and touch it.
> >>>>
> >>>
> >>> The physical hardware component is the GPIO pin, which is what you
> >>> can only
> >> touch.
> >>
> >> No. The regulator is the chip.
> >>
> >
> > In the definition of dts node below, where is the chip? The real hardware is just
> a GPIO Pin.
> >     reg1: regulator-1 {
> >       compatible = "regulator-fixed";
> >       regulator-name = "REG1";
> >       regulator-min-microvolt = <3000000>;
> >       regulator-max-microvolt = <3000000>;
> >       gpio = <&lsio_gpio4 19 GPIO_ACTIVE_HIGH>;
> >       enable-active-high;
> >     };
> 
> There is a chip. This is the chip. If you have there only GPIO pin, then your DTS is
> just wrong. Drop it. If you learn from wrong DTS, then sure, power-domain-
> regulator seems like great idea...
> 

When you talk about the chip, can you please be more specific?

Regarding the dts node, how about the example in the fixed-regulator.yaml under the bindings directory.

    reg_1v8: regulator-1v8 {
      compatible = "regulator-fixed";
      regulator-name = "1v8";
      regulator-min-microvolt = <1800000>;
      regulator-max-microvolt = <1800000>;
      gpio = <&gpio1 16 0>;
      startup-delay-us = <70000>;
      enable-active-high;
      regulator-boot-on;
      gpio-open-drain;
      vin-supply = <&parent_reg>;
    };

If you take a look at the fixed regulator driver (fixed.c), I don't think you'll find anything related to a hardware 
component (chip) other than the GPIO Pin.

Thanks,
Shenwei

> >
> >>> The regulator functions virtually through software layer above of
> >>> the GPIO driver. While we may call it a "regulator" or whatever
> >>> else, this cannot obscure the fact that the underlying hardware is
> >>> just a GPIO pin being
> >> used in a specialized way.
> >>
> >> The regulator is some tiny little box, you can touch and called
> >> ti,tps51632 or similar.
> >>
> >
> > We are talking about the specific "regulator-fixed" driver, why did you bring up
> "ti,tps51632" here?
> 
> Just an example. Can be TPS123098.
> 
> Best regards,
> Krzysztof