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Date:   Thu, 18 May 2023 22:51:09 -0500
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To:     Jisheng Zhang <jszhang@kernel.org>
Cc:     linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
        devicetree@vger.kernel.org, linux-serial@vger.kernel.org,
        Palmer Dabbelt <palmer@rivosinc.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Marc Zyngier <maz@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>
References: <20230518152244.2178-1-jszhang@kernel.org>
 <20230518152244.2178-8-jszhang@kernel.org>
From:   Samuel Holland <samuel@sholland.org>
Subject: Re: [PATCH v4 07/10] riscv: dts: bouffalolab: add the bl808 SoC base
 device tree
In-Reply-To: <20230518152244.2178-8-jszhang@kernel.org>
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Hi Jisheng,

On 5/18/23 10:22, Jisheng Zhang wrote:
> Add a baisc dtsi for the bouffalolab bl808 SoC.
> 
> Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
> ---
>  arch/riscv/boot/dts/bouffalolab/bl808.dtsi | 73 ++++++++++++++++++++++
>  1 file changed, 73 insertions(+)
>  create mode 100644 arch/riscv/boot/dts/bouffalolab/bl808.dtsi
> 
> diff --git a/arch/riscv/boot/dts/bouffalolab/bl808.dtsi b/arch/riscv/boot/dts/bouffalolab/bl808.dtsi
> new file mode 100644
> index 000000000000..87906fe51db5
> --- /dev/null
> +++ b/arch/riscv/boot/dts/bouffalolab/bl808.dtsi
> @@ -0,0 +1,73 @@
> +// SPDX-License-Identifier: (GPL-2.0+ or MIT)
> +/*
> + * Copyright (C) 2022 Jisheng Zhang <jszhang@kernel.org>
> + */
> +
> +#include <dt-bindings/interrupt-controller/irq.h>
> +
> +/ {
> +	compatible = "bouffalolab,bl808";
> +	#address-cells = <1>;
> +	#size-cells = <1>;
> +
> +	cpus {
> +		timebase-frequency = <1000000>;
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +
> +		cpu0: cpu@0 {
> +			compatible = "thead,c906", "riscv";
> +			device_type = "cpu";
> +			reg = <0>;
> +			d-cache-block-size = <64>;
> +			d-cache-sets = <256>;
> +			d-cache-size = <32768>;
> +			i-cache-block-size = <64>;
> +			i-cache-sets = <128>;
> +			i-cache-size = <32768>;
> +			mmu-type = "riscv,sv39";
> +			riscv,isa = "rv64imafdc";
> +
> +			cpu0_intc: interrupt-controller {
> +				compatible = "riscv,cpu-intc";
> +				interrupt-controller;
> +				#address-cells = <0>;
> +				#interrupt-cells = <1>;
> +			};
> +		};
> +	};
> +
> +	xtal: xtal-clk {
> +		compatible = "fixed-clock";
> +		#clock-cells = <0>;
> +		/* This value must be overridden by the board */
> +		clock-frequency = <0>;
> +	};
> +
> +	soc {
> +		compatible = "simple-bus";
> +		ranges;
> +		interrupt-parent = <&plic>;
> +		dma-noncoherent;
> +		#address-cells = <1>;
> +		#size-cells = <1>;
> +
> +		uart3: serial@30002000 {
> +			compatible = "bouffalolab,bl808-uart";
> +			reg = <0x30002000 0x1000>;
> +			interrupts = <20 IRQ_TYPE_LEVEL_HIGH>;
> +			clocks = <&xtal>;

This isn't strictly accurate, and gives you the right frequency if you
are using the vendor "low_load" bootloader. Without that (e.g. when
loading U-Boot directly from the boot ROM), the routing is:

 MM_MUXPLL_160M / 1 => MM_BCLK1X
 MM_BCLK1X / 1 => MM_UART

So this UART module clock is 160 MHz, not 40 MHz.

The way to make this work reliably is to add drivers for the clock tree
(from the preliminary work at [1][2], we'll need at least five of them),
but that is a huge effort, so I'm not sure what we want to do for now.

Regards,
Samuel

[1]: https://github.com/openbouffalo/u-boot/commit/3ca800850f30
[2]: https://github.com/openbouffalo/u-boot/commits/bl808/clk-reset

> +			status = "disabled";
> +		};
> +
> +		plic: interrupt-controller@e0000000 {
> +			compatible = "bouffalolab,bl808-plic", "thead,c900-plic";
> +			reg = <0xe0000000 0x4000000>;
> +			interrupts-extended = <&cpu0_intc 11>, <&cpu0_intc 9>;
> +			interrupt-controller;
> +			#address-cells = <0>;
> +			#interrupt-cells = <2>;
> +			riscv,ndev = <82>;
> +		};
> +	};
> +};