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

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Date:   Fri, 11 Nov 2022 17:48:53 +0900
From:   Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
        Masami Hiramatsu <mhiramat@...nel.org>
Cc:     soc@...nel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/5] arm64: dts: uniphier: Add NX1 SoC and boards
 support

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@...00000 {
>>>> +			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@...00000 {
         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@...00000 {
>>>> +			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