linux-kernel - Re: [net-next v4 1/3] dt-bindings: net: dsa: yt921x: Add Motorcomm YT921x switch support

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Message-ID: <a7fc4e8d-453b-49c2-8177-20568431bf81@kernel.org>
Date: Tue, 19 Aug 2025 08:27:08 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Andrew Lunn <andrew@...n.ch>, David Yang <mmyangfl@...il.com>
Cc: netdev@...r.kernel.org, Vladimir Oltean <olteanv@...il.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Simon Horman <horms@...nel.org>,
 Russell King <linux@...linux.org.uk>, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [net-next v4 1/3] dt-bindings: net: dsa: yt921x: Add Motorcomm
 YT921x switch support

On 18/08/2025 18:55, Andrew Lunn wrote:
>> +  motorcomm,switch-id:
>> +    $ref: /schemas/types.yaml#/definitions/uint32
>> +    description: |
>> +      Value selected by Pin SWITCH_ID_1 / SWITCH_ID_0.
>> +
>> +      Up to 4 chips can share the same MII port ('reg' in DT) by giving
>> +      different SWITCH_ID values. The default value should work if only one chip
>> +      is present.
>> +    enum: [0, 1, 2, 3]
>> +    default: 0
> 
> It is like getting blood from a stone.
> 
> So what you are saying is that you have:
> 
>     mdio {
>         #address-cells = <1>;
>         #size-cells = <0>;
> 
>         switch@1d {
>             compatible = "motorcomm,yt9215";
>             /* default 0x1d, alternate 0x0 */
>             reg = <0x1d>;
>             motorcomm,switch-id = <0>;
>             reset-gpios = <&tlmm 39 GPIO_ACTIVE_LOW>;
> ...
> 	}
> 
>         switch@1d {
>             compatible = "motorcomm,yt9215";
>             reg = <0x1d>;
>             motorcomm,switch-id = <1>;
>             reset-gpios = <&tlmm 39 GPIO_ACTIVE_LOW>;
> ...
> 	}
> 
>         switch@1d {
>             compatible = "motorcomm,yt9215";
>             reg = <0x1d>;
>             motorcomm,switch-id = <2>;
>             reset-gpios = <&tlmm 39 GPIO_ACTIVE_LOW>;
> ...
> 	}
>     }
> 
> Have you tested this? My _guess_ is, it does not work.

Regardless if kernel actually works with this, but duplicating unit
address is not supported, so this obviously would be wrong. I guess
that's the answer for switch-id.

Best regards,
Krzysztof