linux-kernel - Re: [PATCH v2 2/3] dt-bindings: mfd: Add Realtek MISC system controller

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Message-ID: <94198d5f-e49f-4b38-8288-3be29efd142b@kernel.org>
Date: Mon, 17 Nov 2025 12:10:46 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Yu-Chun Lin [林祐君] <eleanor.lin@...ltek.com>,
 "afaerber@...e.de" <afaerber@...e.de>, "robh@...nel.org" <robh@...nel.org>,
 "krzk+dt@...nel.org" <krzk+dt@...nel.org>,
 "conor+dt@...nel.org" <conor+dt@...nel.org>, "lee@...nel.org"
 <lee@...nel.org>, James Tai [戴志峰]
 <james.tai@...ltek.com>
Cc: "linux-arm-kernel@...ts.infradead.org"
 <linux-arm-kernel@...ts.infradead.org>,
 "linux-realtek-soc@...ts.infradead.org"
 <linux-realtek-soc@...ts.infradead.org>,
 "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 CY_Huang[黃鉦晏] <cy.huang@...ltek.com>,
 Stanley Chang[昌育德] <stanley_chang@...ltek.com>
Subject: Re: [PATCH v2 2/3] dt-bindings: mfd: Add Realtek MISC system
 controller

On 17/11/2025 12:03, Yu-Chun Lin [林祐君] wrote:
> Hi Conor and Krzysztof,
> 
>> Documentation/devicetree/bindings/mfd/realtek,misc.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/mfd/realtek,misc.yaml
>> b/Documentation/devicetree/bindings/mfd/realtek,misc.yaml
>> new file mode 100644
>> index 000000000000..4f4a9ae250be
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/mfd/realtek,misc.yaml
>> @@ -0,0 +1,72 @@
>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) %YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/mfd/realtek,misc.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: Realtek MISC System Controller
>> +
>> +description:
>> +  The Realtek MISC System Controller is a register area that contains
>> +  miscellaneous system registers for the SoC and serves as a parent
>> +node
>> +  for other functions.
>> +
>> +maintainers:
>> +  - James Tai <james.tai@...ltek.com>
>> +  - Yu-Chun Lin <eleanor.lin@...ltek.com>
>> +
>> +properties:
>> +  compatible:
>> +    items:
>> +      - enum:
>> +          - realtek,misc
> 
> I apologize for the current compatible string, which was initially named
> by referencing existing patterns like 'brcm,misc' and thus violates the
> naming guidance against "wildcards" and general non-SoC specific names.
> 
> Let me explain the purpose of the device node (Realtek system controller).
> 
> This MISC area contains several peripheral sub-modules such as uart,
> watchdog, rtc or i2c ..... These blocks share a unified register region
> implemented as a single hardware module, which remains powered during
> system suspend states (e.g., S3). These blocks share the same MMIO region
> and appear as child nodes under the MISC syscon node. Currently, it

No, you are mixing hardware with DT representation. This device cannot
appear as child node, because there is no such concept in hardware as
child node. You cannot use argument of DT representation when you
justify how this is represented in DT. It is invalid.

You need to start argumentation in terms of hardware.


> includes uart.
> 
> Regarding the current structure, the device node is defined in a kent.dtsi
> and is included by each SoC's DTSI.
> 
> I've considered two ways to write compatible string naming.
> 
> Option 1: Use a single SoC-specific compatible string
> 
> Rename "realtek,misc" to "realtek,rtd1861-misc"
> 
> /* kent.dtsi */
> misc: syscon@... {
>     compatible = "realtek,rtd1861-misc", "syscon", "simple-mfd";
> };
> 
> Pros: Only one compatible string is needed, simplifying maintenance across
> the driver and DTS.
> 
> Cons: Violates the "SoC-specific compatible" rule for other SoCs
> (RTD1501, RTD1920).
> 
> Option 2: SoC-specific + fallback (Compliant but Verbose)
> 
> Define the full list in the schema, and override the compatible string in each SoC DTSI.
> 
> /* schema binding */
> 
> compatible:
>   items:
>     - enum:
>         - realtek,rtd1501-misc
>         - realtek,rtd1861-misc
>         - realtek,rtd1920-misc
>         # ... add new SoCs here
>     - const: realtek,kent-misc
>     - const: syscon
>     - const: simple-mfd
> 
> 
> /* kent.dtsi */
> 
> misc: syscon@... {
>     compatible = "realtek,kent-misc", "syscon", "simple-mfd";
> };
> 
> SoC-specific override (e.g. rtd1920s-smallville.dtsi):
> 
> &misc {
>     compatible = "realtek,rtd1920-misc", "realtek,kent-misc", "syscon",
>                  "simple-mfd";
> };
> 
> Pros: Fully compliant with DT rules
> 
> Cons: Requires override in every SoC file; slight duplication.
> 
> Is Option 2 the expected pattern?
> Thanks for your guidance!
> 

None of them. You need SoC specific compatibles which can be used as
fallbacks for SoC specific compatibles. There is plenty of examples for
this already, but anyway this does not solve the problem that you still
did not properly describe the hardware but instead use your downstream
as arguments.

This will get you nowhere.


Best regards,
Krzysztof