Re: [PATCH v2 5/5] arm64: dts: uniphier: Add NX1 SoC and boards support

[Kunihiko Hayashi]

Hi Krzysztof,

On 2022/11/09 0:11, Krzysztof Kozlowski wrote:
> On 08/11/2022 15:30, Kunihiko Hayashi wrote:
> > Hi Krzysztof,
> >
> > On 2022/11/08 20:13, Krzysztof Kozlowski wrote:
> > > On 07/11/2022 11:34, Kunihiko Hayashi wrote:
> > > > Initial version of devicetree sources for NX1 SoC and boards.
> > > >
> > > > NX1 SoC belongs to the UniPhier armv8 architecture platform, and is
> > > > designed for IoT and AI/ML application fields.
> > >
> > > > +
> > > > +		soc_glue: syscon@1f800000 {
> > > > +			compatible = "socionext,uniphier-nx1-soc-glue",
> > > > +				     "simple-mfd", "syscon";
> > > > +			reg = <0x1f800000 0x2000>;
> > > > +
> > > > +			pinctrl: pinctrl {
> > > > +				compatible = "socionext,uniphier-nx1-pinctrl";
> > >
> > > So instead of documenting the hardware precisily, you have one big bag
> > > for everything under simple-mfd. This is not how the SoC should be
> > > described in DTS.
> >
> > Sorry I don't understand. This is inherited from the previous
> > descriptions,
> > but is there some example to express DTS correctly about that?
>
> I think yes, although it actually depends what is this hardware.
> Generally speaking, do not use simple-mfd and syscon when these are not
> really simple devices. There are quite many in your DTS, which got my
> attention. Instead - have regular device with or without children.
>
> There is no real need to have this a simple-mfd with one children
> without any resources (no address space, no clocks, no interrupts, nothing).
>
> Why this syscon/mfd and pinctrl is not a regular, one device?

The mfd/syscon.yaml says:
  System controller node represents a register region containing a set
  of miscellaneous registers.

The "soc-glue" is exactly this, it contains various register functions
and might be referred to the drivers.

For example in this NX1 dts, ethernet node points to "soc-glue" node.

    eth: ethernet@15000000 {
        compatible = "socionext,uniphier-nx1-ave4";
        ...
        socionext,syscon-phy-mode = <&soc_glue 0>;
    };

Since such register region is not often systematically designed,
it is tough to cut out as specific memory region for "pinctrl".

And more, the existing pinctrl driver uses of_get_parent() and
syscon_node_to_regmap(), so this change breaks compatibility.

> > > > +			};
> > > > +		};
> > > > +
> > > > +		soc-glue@1f900000 {
> > > > +			compatible = "simple-mfd";
> > >
> > > No, it is not allowed on its own. You need a specific compatible and
> > > bindings describing its children.
> >
> > I saw the definition of "simple-mfd" itself is only in mfd/mfd.txt.
> >
> > Currently there are only efuse devices as children, and this space means
> > nothing. I think it had better define the devices directly.
>
> You need to start describe the hardware. efuse is an efuse, not MFD.
> pinctrl is pinctrl not MFD + pinctrl.

This region also has multiple functions, though, the efuse might be
cut out as specific region without "simple-mfd", unlike pinctrl.

Thank you,

---
Best Regards
Kunihiko Hayashi