linux-kernel - Re: [PATCH v12 1/7] dt-bindings: serial: Added secondary clock for RZ/T2H RSCI

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Message-ID: <20250626230913.GA1338561-robh@kernel.org>
Date: Thu, 26 Jun 2025 18:09:13 -0500
From: Rob Herring <robh@...nel.org>
To: Prabhakar <prabhakar.csengg@...il.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Magnus Damm <magnus.damm@...il.com>,
	Wolfram Sang <wsa+renesas@...g-engineering.com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org, devicetree@...r.kernel.org,
	Biju Das <biju.das.jz@...renesas.com>,
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>,
	Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH v12 1/7] dt-bindings: serial: Added secondary clock for
 RZ/T2H RSCI

On Tue, Jun 17, 2025 at 02:44:58PM +0100, Prabhakar wrote:
> From: Thierry Bultel <thierry.bultel.yh@...renesas.com>
> 
> At boot, the default clock is the PCLKM core clock (synchronous
> clock, which is enabled by the bootloader).
> For different baudrates, the asynchronous clock input must be used.
> Clock selection is made by an internal register of RCSI.
> 
> Add the optional "sck", external clock input.
> 
> Also remove the unneeded serial0 alias from the dts example.
> 
> Signed-off-by: Thierry Bultel <thierry.bultel.yh@...renesas.com>
> Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
> Hi Rob,
> As mentioned in the thread [1] below there are no users of the RSCI binding
> hence this change doesn not break any ABI.
> 
> [1] https://lore.kernel.org/all/CAMuHMdUThuWxxznhjvcn5cOFCWOkb5u-fRYwTOoenDRY=4H6FA@mail.gmail.com/

Please state this in the commit message. If you want to break the ABI 
you have to say that you are and why it is okay.

> 
> Cheers, Prabhakar
> ---
>  .../bindings/serial/renesas,rsci.yaml           | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/serial/renesas,rsci.yaml b/Documentation/devicetree/bindings/serial/renesas,rsci.yaml
> index ea879db5f485..1bf255407df0 100644
> --- a/Documentation/devicetree/bindings/serial/renesas,rsci.yaml
> +++ b/Documentation/devicetree/bindings/serial/renesas,rsci.yaml
> @@ -35,10 +35,15 @@ properties:
>        - const: tei
>  
>    clocks:
> -    maxItems: 1
> +    minItems: 2
> +    maxItems: 3
>  
>    clock-names:
> -    const: fck # UART functional clock
> +    minItems: 2
> +    items:
> +      - const: operation
> +      - const: bus
> +      - const: sck # optional external clock input
>  
>    power-domains:
>      maxItems: 1
> @@ -60,10 +65,6 @@ examples:
>      #include <dt-bindings/interrupt-controller/arm-gic.h>
>      #include <dt-bindings/clock/renesas-cpg-mssr.h>
>  
> -    aliases {
> -        serial0 = &sci0;
> -    };
> -
>      sci0: serial@...05000 {
>          compatible = "renesas,r9a09g077-rsci";
>          reg = <0x80005000 0x400>;
> @@ -72,7 +73,7 @@ examples:
>                       <GIC_SPI 592 IRQ_TYPE_EDGE_RISING>,
>                       <GIC_SPI 593 IRQ_TYPE_LEVEL_HIGH>;
>          interrupt-names = "eri", "rxi", "txi", "tei";
> -        clocks = <&cpg CPG_MOD 108>;
> -        clock-names = "fck";
> +        clocks = <&cpg CPG_MOD 8>, <&cpg CPG_CORE 13>;
> +        clock-names = "operation", "bus";
>          power-domains = <&cpg>;
>      };
> -- 
> 2.49.0
>