Re: [PATCH 7/9] RISC-V: add initial LiteX SoC support

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hello Antony,

On 05.05.21 12:08, Antony Pavlov wrote:
> LiteX is a Migen-based System on Chip, supporting softcore
> VexRiscv CPU, a 32-bits Linux Capable RISC-V CPU.
> 
> See https://github.com/enjoy-digital/litex and
> https://github.com/litex-hub/linux-on-litex-vexriscv
> for details.
> 
> Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
> ---
>  arch/riscv/Kconfig                            |   9 ++
>  arch/riscv/Makefile                           |   1 +
>  arch/riscv/dts/litex_soc_linux.dtsi           |  49 +++++++
>  arch/riscv/mach-litex/Kconfig                 |   8 ++
>  arch/riscv/mach-litex/Makefile                |   3 +
>  arch/riscv/mach-litex/include/mach/debug_ll.h | 124 ++++++++++++++++++
>  6 files changed, 194 insertions(+)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index c0583f3153..40dfd7dd93 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -34,6 +34,14 @@ config MACH_ERIZO
>  	select RISCV_M_MODE
>  	select RISCV_TIMER
>  
> +config MACH_LITEX
> +	bool "litex family"
> +	select ARCH_RV32I
> +	select HAS_DEBUG_LL
> +	select HAS_NMON
> +	select USE_COMPRESSED_DTB
> +	select RISCV_SBI
> +
>  config MACH_VIRT
>  	bool "virt family"
>  	select BOARD_RISCV_GENERIC_DT
> @@ -83,6 +91,7 @@ config 64BIT
>  	select PHYS_ADDR_T_64BIT
>  
>  source "arch/riscv/mach-erizo/Kconfig"
> +source "arch/riscv/mach-litex/Kconfig"
>  
>  config BOARD_RISCV_GENERIC_DT
>  	select BOARD_GENERIC_DT
> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> index aba4526bba..bc22786368 100644
> --- a/arch/riscv/Makefile
> +++ b/arch/riscv/Makefile
> @@ -20,6 +20,7 @@ cflags-y += $(riscv-cflags-y)
>  LDFLAGS_barebox += -nostdlib
>  
>  machine-$(CONFIG_MACH_ERIZO)	:= erizo
> +machine-$(CONFIG_MACH_LITEX)	:= litex

Could you rebase on barebox next?
I dropped machine directories for RISC-V. They were only
used for <mach/debug_ll.h> and there is an <asm/debug_ll.h>
now that can be extended instead.

This reduces boilerplate and allows building all RISC-V
images in one go.

>  machine-$(CONFIG_MACH_VIRT)	:= virt
>  
>  LDFLAGS_barebox += $(riscv-ldflags-y)
> diff --git a/arch/riscv/dts/litex_soc_linux.dtsi b/arch/riscv/dts/litex_soc_linux.dtsi
> new file mode 100644
> index 0000000000..32382b8dc2
> --- /dev/null
> +++ b/arch/riscv/dts/litex_soc_linux.dtsi

Is "linux" a well-nown LiteX configuration?
Otherwise would maybe litex-vexrisc.dtsi be a better name?

> @@ -0,0 +1,49 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +/dts-v1/;
> +
> +/ {
> +	compatible = "litex,vexriscv-soc-linux";
> +
> +	#address-cells = <1>;
> +	#size-cells = <1>;
> +
> +	cpus {
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +
> +		timebase-frequency = <100000000>; // 100 MHz
> +
> +		cpu@0 {
> +			device_type = "cpu";
> +			compatible = "spinalhdl,vexriscv", "riscv";
> +			reg = <0>;
> +		};
> +	};
> +
> +	uart0: serial@f0001000 {
> +		compatible = "litex,uart";
> +		reg = <0xf0001000 0x18>;
> +		status = "disabled";
> +	};
> +
> +	mac0: mac@f0009000 {
> +		compatible = "litex,liteeth";
> +		reg = <0xf0009000 0x7c /* base */
> +			0xf0009800 0x0a /* mdio_base */
> +			0xb0000000 0x2000>; /* buf_base */
> +		tx-fifo-depth = <2>;
> +		rx-fifo-depth = <2>;
> +		status = "disabled";
> +	};
> +
> +	spi0: spi@f000b800 {
> +		compatible = "litex,spiflash";
> +
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +
> +		reg = <0xf000b800 0x100>;
> +		status = "disabled";
> +	};
> +};
> diff --git a/arch/riscv/mach-litex/Kconfig b/arch/riscv/mach-litex/Kconfig
> new file mode 100644
> index 0000000000..19d5927e44
> --- /dev/null
> +++ b/arch/riscv/mach-litex/Kconfig
> @@ -0,0 +1,8 @@
> +if MACH_LITEX
> +
> +choice
> +	prompt "Board type"
> +
> +endchoice
> +
> +endif
> diff --git a/arch/riscv/mach-litex/Makefile b/arch/riscv/mach-litex/Makefile
> new file mode 100644
> index 0000000000..d9c51e74c3
> --- /dev/null
> +++ b/arch/riscv/mach-litex/Makefile
> @@ -0,0 +1,3 @@
> +# just to build a built-in.o. Otherwise compilation fails when no o-files is
> +# created.
> +obj- += dummy.o
> diff --git a/arch/riscv/mach-litex/include/mach/debug_ll.h b/arch/riscv/mach-litex/include/mach/debug_ll.h
> new file mode 100644
> index 0000000000..df7032716d
> --- /dev/null
> +++ b/arch/riscv/mach-litex/include/mach/debug_ll.h
> @@ -0,0 +1,124 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2019 Antony Pavlov <antonynpavlov@gmail.com>
> + *
> + * This file is part of barebox.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + */
> +
> +#ifndef __MACH_LITEX_DEBUG_LL__
> +#define __MACH_LITEX_DEBUG_LL__
> +
> +/** @file
> + *  This File contains declaration for early output support
> + */
> +
> +#include <linux/kconfig.h>
> +
> +#define DEBUG_LL_UART_ADDR	0xf0001000
> +#define UART_RXTX	0x00
> +#define UART_TXFULL	0x04
> +#define UART_RXEMPTY	0x08
> +#define UART_EV_PENDING	0x10
> +#define  UART_EV_RX	(1 << 1)
> +#define UART_EV_ENABLE	0x14
> +
> +
> +#ifndef __ASSEMBLY__
> +
> +/*
> + * C macros
> + */
> +
> +#include <asm/io.h>
> +
> +static inline void PUTC_LL(char ch)
> +{
> +#ifdef CONFIG_DEBUG_LL
> +	/* wait for space */
> +	while (__raw_readb((u8 *)DEBUG_LL_UART_ADDR + UART_TXFULL))
> +		;
> +
> +	__raw_writeb(ch, (u8 *)DEBUG_LL_UART_ADDR + UART_RXTX);
> +#endif /* CONFIG_DEBUG_LL */
> +}
> +#else /* __ASSEMBLY__ */
> +/*
> + * Macros for use in assembly language code
> + */
> +
> +/*
> + * output a character in a0
> + */
> +.macro	debug_ll_outc_a0
> +#ifdef CONFIG_DEBUG_LL
> +
> +	li	t0, DEBUG_LL_UART_ADDR
> +
> +201:
> +	lbu	t1, UART_TXFULL(t0)	/* uart tx full ? */
> +	andi	t1, t1, 0xff
> +	bnez	t1, 201b		/* try again */
> +
> +	sb	a0, UART_RXTX(t0)	/* write the character */
> +
> +#endif /* CONFIG_DEBUG_LL */
> +.endm
> +
> +/*
> + * output a character
> + */
> +.macro	debug_ll_outc chr
> +#ifdef CONFIG_DEBUG_LL
> +	li	a0, \chr
> +	debug_ll_outc_a0
> +#endif /* CONFIG_DEBUG_LL */
> +.endm
> +
> +/*
> + * check character in input buffer
> + * return value:
> + *  v0 = 0   no character in input buffer
> + *  v0 != 0  character in input buffer
> + */
> +.macro	debug_ll_tstc
> +#ifdef CONFIG_DEBUG_LL
> +	li	t0, DEBUG_LL_UART_ADDR
> +
> +	/* get line status and check for data present */
> +	lbu	s0, UART_RXEMPTY(t0)
> +	bnez    s0, 243f
> +	li	s0, 1
> +	j	244f
> +243:	li	s0, 0
> +244:	nop
> +#endif /* CONFIG_DEBUG_LL */
> +.endm
> +
> +/*
> + * get character to v0
> + */
> +.macro	debug_ll_getc
> +#ifdef CONFIG_DEBUG_LL
> +
> +204:
> +	debug_ll_tstc
> +
> +	/* try again */
> +	beqz	s0, 204b
> +
> +	/* read a character */
> +	lb	s0, UART_RXTX(t0)
> +	li      t1, UART_EV_RX
> +	sb	t1, UART_EV_PENDING(t0)
> +
> +#endif /* CONFIG_DEBUG_LL */
> +.endm
> +#endif /* __ASSEMBLY__ */
> +
> +#endif /* __MACH_LITEX_DEBUG_LL__ */

Given that we jump into C very early now, do we still need
the assembly debug_ll helpers?

Cheers,
Ahmad

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