linux-kernel - Re: [PATCH] arm64: dts: ti: k3-am64-mcu: explicitly assign UART base clock rates

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Date:   Fri, 15 Apr 2022 13:10:51 +0530
From:   Vignesh Raghavendra <vigneshr@...com>
To:     Matthias Schiffer <matthias.schiffer@...tq-group.com>,
        Nishanth Menon <nm@...com>, Tero Kristo <kristo@...nel.org>
CC:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: dts: ti: k3-am64-mcu: explicitly assign UART base
 clock rates



On 11/04/22 5:41 pm, Matthias Schiffer wrote:
> We found that (at least some versions of) the sci-fw do not assign the
> expected base clock rate of 48 MHz for the UARTs in the MCU domain,
> leading to incorrect baud rates when used from Linux. Use
> assigned-clock-rates to fix this issue.
> 
> Fixes: 8abae9389bdb ("arm64: dts: ti: Add support for AM642 SoC")
> Signed-off-by: Matthias Schiffer <matthias.schiffer@...tq-group.com>
> ---
> 
> I'm not sure if this is the best fix. Should the clock-frequency
> property simply be removed, so the frequency is queried from the clock
> driver instead?
> 

I think its better to drop clock-frequency. Driver can setup DLL/DLH to
get appropriate baudrate as per frequency queried from clock driver

>  arch/arm64/boot/dts/ti/k3-am64-mcu.dtsi | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/ti/k3-am64-mcu.dtsi b/arch/arm64/boot/dts/ti/k3-am64-mcu.dtsi
> index 2bb5c9ff172c..69b0f127eea5 100644
> --- a/arch/arm64/boot/dts/ti/k3-am64-mcu.dtsi
> +++ b/arch/arm64/boot/dts/ti/k3-am64-mcu.dtsi
> @@ -15,6 +15,8 @@ mcu_uart0: serial@...0000 {
>  		power-domains = <&k3_pds 149 TI_SCI_PD_EXCLUSIVE>;
>  		clocks = <&k3_clks 149 0>;
>  		clock-names = "fclk";
> +		assigned-clocks = <&k3_clks 149 0>;
> +		assigned-clock-rates = <48000000>;
>  	};
>  
>  	mcu_uart1: serial@...0000 {
> @@ -26,6 +28,8 @@ mcu_uart1: serial@...0000 {
>  		power-domains = <&k3_pds 160 TI_SCI_PD_EXCLUSIVE>;
>  		clocks = <&k3_clks 160 0>;
>  		clock-names = "fclk";
> +		assigned-clocks = <&k3_clks 160 0>;
> +		assigned-clock-rates = <48000000>;
>  	};
>  
>  	mcu_i2c0: i2c@...0000 {