We add RISC-V semihosting based serial console for JTAG based early debugging.
The RISC-V semihosting specification is available at: https://github.com/riscv/riscv-semihosting-spec/blob/main/riscv-semihosting-spec.adoc Signed-off-by: Anup Patel <apa...@ventanamicro.com> Signed-off-by: Kautuk Consul <kcon...@ventanamicro.com> --- arch/riscv/Kconfig | 47 ++++++++++++++++++++++++++++ arch/riscv/include/asm/semihosting.h | 11 +++++++ arch/riscv/include/asm/spl.h | 1 + arch/riscv/lib/Makefile | 2 ++ arch/riscv/lib/interrupts.c | 11 +++++++ arch/riscv/lib/semihosting.c | 24 ++++++++++++++ 6 files changed, 96 insertions(+) create mode 100644 arch/riscv/include/asm/semihosting.h create mode 100644 arch/riscv/lib/semihosting.c diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index 78e964db12..b15d9028bd 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -371,4 +371,51 @@ config TPL_USE_ARCH_MEMSET endmenu +config SEMIHOSTING + bool "Support RISCV semihosting" + select LIB_SEMIHOSTING + help + Semihosting is a method for a target to communicate with a host + debugger. It uses special instructions which the debugger will trap + on and interpret. This allows U-Boot to read/write files, print to + the console, and execute arbitrary commands on the host system. + + Enabling this option will add support for reading and writing files + on the host system. If you don't have a debugger attached then trying + to do this will likely cause U-Boot to hang. Say 'n' if you are unsure. + +config SEMIHOSTING_FALLBACK + bool "Recover gracefully when semihosting fails" + depends on SEMIHOSTING && RISCV + default y + help + Normally, if U-Boot makes a semihosting call and no debugger is + attached, then it will panic due to a synchronous abort + exception. This config adds an exception handler which will allow + U-Boot to recover. Say 'y' if unsure. + +config SPL_SEMIHOSTING + bool "Support RISCV semihosting in SPL" + depends on SPL + select LIB_SEMIHOSTING + help + Semihosting is a method for a target to communicate with a host + debugger. It uses special instructions which the debugger will trap + on and interpret. This allows U-Boot to read/write files, print to + the console, and execute arbitrary commands on the host system. + + Enabling this option will add support for reading and writing files + on the host system. If you don't have a debugger attached then trying + to do this will likely cause U-Boot to hang. Say 'n' if you are unsure. + +config SPL_SEMIHOSTING_FALLBACK + bool "Recover gracefully when semihosting fails in SPL" + depends on SPL_SEMIHOSTING && RISCV + default y + help + Normally, if U-Boot makes a semihosting call and no debugger is + attached, then it will panic due to a synchronous abort + exception. This config adds an exception handler which will allow + U-Boot to recover. Say 'y' if unsure. + endmenu diff --git a/arch/riscv/include/asm/semihosting.h b/arch/riscv/include/asm/semihosting.h new file mode 100644 index 0000000000..7042821e00 --- /dev/null +++ b/arch/riscv/include/asm/semihosting.h @@ -0,0 +1,11 @@ +/* SPDX-License-Identifier: GPL-2.0+ */ +/* + * Copyright (C) 2022 Ventana Micro Systems Inc. + */ + +#ifndef __ASM_RISCV_SEMIHOSTING_H +#define __ASM_RISCV_SEMIHOSTING_H + +long smh_trap(int sysnum, void *addr); + +#endif /* __ASM_RISCV_SEMIHOSTING_H */ diff --git a/arch/riscv/include/asm/spl.h b/arch/riscv/include/asm/spl.h index e8a94fcb1f..2898a770ee 100644 --- a/arch/riscv/include/asm/spl.h +++ b/arch/riscv/include/asm/spl.h @@ -25,6 +25,7 @@ enum { BOOT_DEVICE_DFU, BOOT_DEVICE_XIP, BOOT_DEVICE_BOOTROM, + BOOT_DEVICE_SMH, BOOT_DEVICE_NONE }; diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile index 06020fcc2a..64e29804c1 100644 --- a/arch/riscv/lib/Makefile +++ b/arch/riscv/lib/Makefile @@ -42,3 +42,5 @@ extra-$(CONFIG_EFI) += $(EFI_CRT0) $(EFI_RELOC) obj-$(CONFIG_$(SPL_TPL_)USE_ARCH_MEMSET) += memset.o obj-$(CONFIG_$(SPL_TPL_)USE_ARCH_MEMMOVE) += memmove.o obj-$(CONFIG_$(SPL_TPL_)USE_ARCH_MEMCPY) += memcpy.o + +obj-$(CONFIG_$(SPL_TPL_)SEMIHOSTING) += semihosting.o diff --git a/arch/riscv/lib/interrupts.c b/arch/riscv/lib/interrupts.c index 100be2e966..bd7cd772b8 100644 --- a/arch/riscv/lib/interrupts.c +++ b/arch/riscv/lib/interrupts.c @@ -17,6 +17,7 @@ #include <asm/ptrace.h> #include <asm/system.h> #include <asm/encoding.h> +#include <semihosting.h> DECLARE_GLOBAL_DATA_PTR; @@ -149,6 +150,16 @@ ulong handle_trap(ulong cause, ulong epc, ulong tval, struct pt_regs *regs) /* An UEFI application may have changed gd. Restore U-Boot's gd. */ efi_restore_gd(); + if (cause == CAUSE_BREAKPOINT && + CONFIG_IS_ENABLED(SEMIHOSTING_FALLBACK)) { + /* For semihosting fallback we simply skip the ebreak + * instruction. + */ + disable_semihosting(); + epc += 4; + return epc; + } + is_irq = (cause & MCAUSE_INT); irq = (cause & ~MCAUSE_INT); diff --git a/arch/riscv/lib/semihosting.c b/arch/riscv/lib/semihosting.c new file mode 100644 index 0000000000..72ea9521dc --- /dev/null +++ b/arch/riscv/lib/semihosting.c @@ -0,0 +1,24 @@ +// SPDX-License-Identifier: GPL-2.0+ +/* + * Copyright (C) 2022 Ventana Micro Systems Inc. + */ + +#include <common.h> + +long smh_trap(int sysnum, void *addr) +{ + register int ret asm ("a0") = sysnum; + register void *param0 asm ("a1") = addr; + + asm volatile ("\t.option push\n" + "\t.option norvc\n" + "\tj 1f\n" + "\t.align 4\n" + "\t1: slli zero, zero, 0x1f\n" + "\tebreak\n" + "\tsrai zero, zero, 7\n" + "\t.option pop\n" + : "+r" (ret) : "r" (param0) : "memory"); + + return ret; +} -- 2.34.1