linux-kernel - Re: [PATCH] riscv: dts: spacemit: uart: set dummy clock to silent dt warning

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Message-ID: <22fd8b89-b937-48db-a5bf-4e468441b206@iscas.ac.cn>
Date: Sat, 19 Jul 2025 15:48:13 +0800
From: Vivian Wang <wangruikang@...as.ac.cn>
To: Yixun Lan <dlan@...too.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Paul Walmsley <paul.walmsley@...ive.com>,
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 Alexandre Ghiti <alex@...ti.fr>
Cc: devicetree@...r.kernel.org, linux-riscv@...ts.infradead.org,
 spacemit@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: dts: spacemit: uart: set dummy clock to silent dt
 warning

On 7/18/25 23:13, Yixun Lan wrote:
> sec_uart1 is reserved in DT, and no clock is implemented in the CCF
> framework, thus 'make dtbs_check' will eject this warning message:
>   serial@...12000: 'clock-names' is a required property
>
> So, adding a dummy clock to the device tree to fulfill the clock
> requirement, then silent this dt check warning.

NAK. This is definitely worse than the warning.

Honestly, if you don't like this warning, I think we should just drop
the node. If not...

>
> Signed-off-by: Yixun Lan <dlan@...too.org>
> ---
>  arch/riscv/boot/dts/spacemit/k1.dtsi | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/boot/dts/spacemit/k1.dtsi b/arch/riscv/boot/dts/spacemit/k1.dtsi
> index c0f8c5fca975d73b6ea6886da13fcf55289cb16c..e9b98f2a3b1cc38f569d7de336630df846cbfbe7 100644
> --- a/arch/riscv/boot/dts/spacemit/k1.dtsi
> +++ b/arch/riscv/boot/dts/spacemit/k1.dtsi
> @@ -309,6 +309,13 @@ cluster1_l2_cache: l2-cache1 {
>  	};
>  
>  	clocks {
> +		clk_dummy: clock-dummy {
> +			compatible = "fixed-clock";
> +			#clock-cells = <0>;
> +			clock-frequency = <0>;

That can't be right for UART, which depends on knowing about the baud
clock rate. If we want a fixed clock to represent whatever the "secure"
clock controller has at least it should be set to the nominal frequency.

Vivian "dramforever" Wang

> +			clock-output-names = "clk_dummy";
> +		};
> +
>  		vctcxo_1m: clock-1m {
>  			compatible = "fixed-clock";
>  			clock-frequency = <1000000>;
> @@ -556,8 +563,9 @@ clint: timer@...00000 {
>  		sec_uart1: serial@...12000 {
>  			compatible = "spacemit,k1-uart", "intel,xscale-uart";
>  			reg = <0x0 0xf0612000 0x0 0x100>;
> +			clocks = <&clk_dummy>, <&clk_dummy>;
> +			clock-names = "core", "bus";
>  			interrupts = <43>;
> -			clock-frequency = <14857000>;
>  			reg-shift = <2>;
>  			reg-io-width = <4>;
>  			status = "reserved"; /* for TEE usage */
>
> ---
> base-commit: 19272b37aa4f83ca52bdf9c16d5d81bdd1354494
> change-id: 20250718-02-k1-uart-clock-0beb9ef10fe0
>
> Best regards,