Re: [PATCH 08/10] riscv: Add Kendryte K210 device tree

[Sean Anderson <seanga2@gmail.com>]

On 2/12/20 5:34 AM, Damien Le Moal wrote:
> Add a generic device tree for Kendryte K210 SoC based boards. This (for
> now) very simple device tree works for the Kendryte KD233 development
> board, the Sipeed MAIX M1 Dock based boards and the Sipeed MAIXDUINO
> board.
> 
> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
> ---
>  arch/riscv/boot/dts/Makefile           |   1 +
>  arch/riscv/boot/dts/kendryte/Makefile  |   2 +
>  arch/riscv/boot/dts/kendryte/k210.dts  |  23 +++++
>  arch/riscv/boot/dts/kendryte/k210.dtsi | 123 +++++++++++++++++++++++++
>  4 files changed, 149 insertions(+)
>  create mode 100644 arch/riscv/boot/dts/kendryte/Makefile
>  create mode 100644 arch/riscv/boot/dts/kendryte/k210.dts
>  create mode 100644 arch/riscv/boot/dts/kendryte/k210.dtsi
> 
> diff --git a/arch/riscv/boot/dts/Makefile b/arch/riscv/boot/dts/Makefile
> index 0bf2669aa12d..87815557f2db 100644
> --- a/arch/riscv/boot/dts/Makefile
> +++ b/arch/riscv/boot/dts/Makefile
> @@ -3,4 +3,5 @@ ifneq ($(CONFIG_BUILTIN_DTB_SOURCE),"")
>  obj-$(CONFIG_USE_BUILTIN_DTB) += $(patsubst "%",%,$(CONFIG_BUILTIN_DTB_SOURCE)).dtb.o
>  else
>  subdir-y += sifive
> +subdir-y += kendryte
>  endif
> diff --git a/arch/riscv/boot/dts/kendryte/Makefile b/arch/riscv/boot/dts/kendryte/Makefile
> new file mode 100644
> index 000000000000..815444e69e89
> --- /dev/null
> +++ b/arch/riscv/boot/dts/kendryte/Makefile
> @@ -0,0 +1,2 @@
> +# SPDX-License-Identifier: GPL-2.0
> +dtb-$(CONFIG_SOC_KENDRYTE) += k210.dtb
> diff --git a/arch/riscv/boot/dts/kendryte/k210.dts b/arch/riscv/boot/dts/kendryte/k210.dts
> new file mode 100644
> index 000000000000..0d1f28fce6b2
> --- /dev/null
> +++ b/arch/riscv/boot/dts/kendryte/k210.dts
> @@ -0,0 +1,23 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Copyright (C) 2020 Western Digital Corporation or its affiliates.
> + */
> +
> +/dts-v1/;
> +
> +#include "k210.dtsi"
> +
> +/ {
> +	model = "Kendryte K210 generic";
> +	compatible = "kendryte,k210";
> +
> +	chosen {
> +		bootargs = "earlycon console=ttySIF0";
> +		stdout-path = "serial0";
> +	};
> +};
> +
> +&uarths0 {
> +	status = "okay";
> +};
> +
> diff --git a/arch/riscv/boot/dts/kendryte/k210.dtsi b/arch/riscv/boot/dts/kendryte/k210.dtsi
> new file mode 100644
> index 000000000000..4b9eeabb07f7
> --- /dev/null
> +++ b/arch/riscv/boot/dts/kendryte/k210.dtsi
> @@ -0,0 +1,123 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Copyright (C) 2019 Sean Anderson <seanga2@gmail.com>

Glad to see this is getting some use :)

This appears to be an old-ish version, and I've made some updates in the
past month or so. My current work is availible from [1].

[1] https://github.com/Forty-Bot/u-boot/blob/maix_v6/arch/riscv/dts/k210.dtsi

> + * Copyright (C) 2020 Western Digital Corporation or its affiliates.
> + */
> +
> +/ {
> +	/*
> +	 * Although the K210 is a 64-bit CPU, the address bus is only 32-bits
> +	 * wide, and the upper half of all addresses is ignored.
> +	 */
> +	#address-cells = <1>;
> +	#size-cells = <1>;
> +	compatible = "kendryte,k210";
> +
> +	aliases {
> +		serial0 = &uarths0;
> +	};
> +
> +	clocks {
> +		in0: oscillator {
> +			compatible = "fixed-clock";
> +			#clock-cells = <0>;
> +			clock-frequency = <26000000>;
> +		};
> +	};
> +
> +	cpus {
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +		timebase-frequency = <7800000>;

This is true only for the default frequency. I wonder if there is a
better way to encode this.

> +		cpu0: cpu@0 {
> +			device_type = "cpu";
> +			reg = <0>;
> +			compatible = "riscv";
> +			riscv,isa = "rv64imafdc";
> +			mmu-type = "none";

This should be "sv36".

> +			i-cache-size = <0x8000>;
> +			i-cache-block-size = <64>; /* bogus */

I emailed some people at Kendryte and they confirmed the 64-byte
cacheline. The cpus are rocket cores.

> +			d-cache-size = <0x8000>;
> +			d-cache-block-size = <64>; /* bogus */
> +			clocks = <&sysctl 0>;

This is correct only by coincidence. The clock structure is

in0 -> pll0 -> aclk -> cpu

aclk divides by two by default, so it runs at 390 MHz, which is also
what you set pll1 to. However, if someone else (such as the bootloader)
changes the pll0 frequency then this will be completely off.

> +			clock-frequency = <390000000>;
> +			cpu0_intc: interrupt-controller {
> +				#interrupt-cells = <1>;
> +				interrupt-controller;
> +				compatible = "riscv,cpu-intc";
> +			};
> +		};
> +		cpu1: cpu@1 {
> +			device_type = "cpu";
> +			reg = <1>;
> +			compatible = "riscv";
> +			riscv,isa = "rv64imafdc";
> +			mmu-type = "none";
> +			i-cache-size = <0x8000>;
> +			i-cache-block-size = <64>; /* bogus */
> +			d-cache-size = <0x8000>;
> +			d-cache-block-size = <64>; /* bogus */
> +			clocks = <&sysctl 0>;
> +			clock-frequency = <390000000>;
> +			cpu1_intc: interrupt-controller {
> +				#interrupt-cells = <1>;
> +				interrupt-controller;
> +				compatible = "riscv,cpu-intc";
> +			};
> +		};
> +	};
> +
> +	sram0: memory@80000000 {
> +		device_type = "memory";
> +		reg = <0x80000000 0x400000>;
> +	};
> +
> +	sram1: memory@80400000 {
> +		device_type = "memory";
> +		reg = <0x80400000 0x200000>;
> +	};
> +
> +	kpu_sram: memory@80600000 {
> +		device_type = "memory";
> +		reg = <0x80600000 0x200000>;
> +	};
> +
> +	soc {
> +		#address-cells = <1>;
> +		#size-cells = <1>;
> +		compatible = "kendryte,k210-soc", "simple-bus";

Should the -soc suffix be here? I saw it was absent from the fu540
device tree.

> +		ranges;
> +		interrupt-parent = <&plic0>;
> +
> +		sysctl: sysctl@50440000 {
> +			compatible = "kendryte,k210-sysctl", "syscon";
> +			reg = <0x50440000 0x1000>;
> +			#clock-cells = <1>;
> +		};

Would it be possible to model this as an MFD? There are a lot of
different registers in here, many of which are unrelated to clocks. For
example, there are also reset registers, a reboot register, and DMA
handshake controls. I think modeling this as a clock controller only
does not correctly reflect the hardware, and will be awkward in the
future.

> +
> +		clint0: interrupt-controller@2000000 {
> +			compatible = "riscv,clint0";
> +			reg = <0x2000000 0xC000>;
> +			interrupts-extended = <&cpu0_intc 3>,  <&cpu1_intc 3>;
> +			clocks = <&sysctl 0>;

Again, this is wrong; it should be running off ACLK.

> +		};
> +
> +		plic0: interrupt-controller@c000000 {
> +			#interrupt-cells = <1>;
> +			interrupt-controller;
> +			compatible = "kendryte,k210-plic0", "riscv,plic0";
> +			reg = <0xC000000 0x3FFF008>;

With regard to the size of registers, I had the following exchange on
the U-Boot mailing list.

On Tue, Feb 4, 2020 at 10:23 PM Sean Anderson <seanga2@gmail.com> wrote:
>
> On 2/4/20 6:32 AM, Bin Meng wrote:
>> Hi Sean,
>>
>> On Mon, Feb 3, 2020 at 4:10 AM Sean Anderson <seanga2@gmail.com> wrote:
>>> Should the size of a reg be the size of the documented registers, or the size
>>> of the address space which will be routed to that device?
>>
>> Perhaps we need use the size of the address space routed to that
>> device, in case there is some undocumented registers we need handle.
>
> Ok, I'll go with the whole address space then.

You may want to make similar changes for Linux; I didn't see any
documentation about what the preferred size was.

> +			interrupts-extended = <&cpu0_intc 11>, <&cpu0_intc 0xffffffff>,
> +					      <&cpu1_intc 11>, <&cpu1_intc 0xffffffff>;
> +			riscv,ndev = <65>;
> +			riscv,max-priority = <0x07>;
> +		};
> +
> +		uarths0: serial@38000000 {
> +			compatible = "kendryte,k210-uart0", "sifive,uart0";

I would change the first compatible string to "kendryte,k210-uarths",
since that is how this uart is described in their documentation.

> +			reg = <0x38000000 0x20>;

Same thing as the size comments above.

> +			interrupts = <33>;
> +			clocks = <&sysctl 0>;

Same clock comments.

> +		};
> +	};
> +};
> 

--Sean