Re: [PATCH v6 4/5] arm64: dts: qcom: Add CMN PLL node for IPQ9574 SoC

[Konrad Dybcio]

On 7.11.2024 10:50 AM, Luo Jie wrote:
> The CMN PLL clock controller allows selection of an input clock rate
> from a defined set of input clock rates. It in-turn supplies fixed
> rate output clocks to the hardware blocks that provide the ethernet
> functions such as PPE (Packet Process Engine) and connected switch or
> PHY, and to GCC.
> 
> The reference clock of CMN PLL is routed from XO to the CMN PLL through
> the internal WiFi block.
> .XO (48 MHZ or 96 MHZ)-->WiFi (multiplier/divider)-->48 MHZ to CMN PLL.
> 
> The reference input clock from WiFi to CMN PLL is fully controlled by
> the bootstrap pins which select the XO frequency (48 MHZ or 96 MHZ).
> Based on this frequency, the divider in the internal Wi-Fi block is
> automatically configured by hardware (1 for 48 MHZ, 2 for 96 MHZ), to
> ensure output clock to CMN PLL is 48 MHZ.
> 
> Signed-off-by: Luo Jie <quic_luoj@xxxxxxxxxxx>
> ---
>  arch/arm64/boot/dts/qcom/ipq9574-rdp-common.dtsi | 16 ++++++++++++++-
>  arch/arm64/boot/dts/qcom/ipq9574.dtsi            | 26 +++++++++++++++++++++++-
>  2 files changed, 40 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/boot/dts/qcom/ipq9574-rdp-common.dtsi b/arch/arm64/boot/dts/qcom/ipq9574-rdp-common.dtsi
> index 91e104b0f865..78f6a2e053d5 100644
> --- a/arch/arm64/boot/dts/qcom/ipq9574-rdp-common.dtsi
> +++ b/arch/arm64/boot/dts/qcom/ipq9574-rdp-common.dtsi
> @@ -3,7 +3,7 @@
>   * IPQ9574 RDP board common device tree source
>   *
>   * Copyright (c) 2020-2021 The Linux Foundation. All rights reserved.
> - * Copyright (c) 2023, Qualcomm Innovation Center, Inc. All rights reserved.
> + * Copyright (c) 2023-2024, Qualcomm Innovation Center, Inc. All rights reserved.
>   */
>  
>  /dts-v1/;
> @@ -164,6 +164,20 @@ &usb3 {
>  	status = "okay";
>  };
>  
> +/*
> + * The bootstrap pins for the board select the XO clock frequency,
> + * which automatically enables the right dividers to ensure the
> + * reference clock output from WiFi is 48 MHZ.

I'm a bit puzzled by this comment. Does it mean this clock could
run at some different speeds?

[...]

>  
> +		cmn_pll: clock-controller@9b000 {
> +			compatible = "qcom,ipq9574-cmn-pll";
> +			reg = <0x0009b000 0x800>;
> +			clocks = <&ref_48mhz_clk>,
> +				 <&gcc GCC_CMN_12GPLL_AHB_CLK>,
> +				 <&gcc GCC_CMN_12GPLL_SYS_CLK>;
> +			clock-names = "ref", "ahb", "sys";
> +			#clock-cells = <1>;
> +			assigned-clocks = <&cmn_pll CMN_PLL_CLK>;
> +			assigned-clock-rates-u64 = /bits/ 64 <12000000000>;

Does devlink not complain about self-referencing the clock here?

Konrad