On 9/19/22 7:49 AM, Kautuk Consul wrote:
> 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/include/asm/spl.h | 1 +
> arch/riscv/lib/Makefile | 2 ++
> arch/riscv/lib/interrupts.c | 11 +++++++++++
> arch/riscv/lib/semihosting.c | 24 ++++++++++++++++++++++++
> lib/Kconfig | 6 +++---
> 5 files changed, 41 insertions(+), 3 deletions(-)
> create mode 100644 arch/riscv/lib/semihosting.c
>
> 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)) {
Hm, shouldn't we check to see if this is actually a semihosting
breakpoint? This involves reading the prior and posterior
instructions, which might be a bit too much. Alternatively, we
could only take this trap if semihosting_enabled(), which would
limit any suppression of spurious breakpoints to one instruction.
> + /* 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..d6593b02a6
> --- /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 (".align 4\n"
> + ".option push\n"
> + ".option norvc\n"
> +
> + "slli zero, zero, 0x1f\n"
> + "ebreak\n"
> + "srai zero, zero, 7\n"
> + ".option pop\n"
> + : "+r" (ret) : "r" (param0) : "memory");
> +
> + return ret;
> +}
> diff --git a/lib/Kconfig b/lib/Kconfig
> index 97920e7552..eed3a231d9 100644
> --- a/lib/Kconfig
> +++ b/lib/Kconfig
> @@ -85,7 +85,7 @@ config SEMIHOSTING
>
> config SEMIHOSTING_FALLBACK
> bool "Recover gracefully when semihosting fails"
> - depends on SEMIHOSTING && ARM64
> + depends on SEMIHOSTING && (ARM64 || RISCV)
> default y
> help
> Normally, if U-Boot makes a semihosting call and no debugger is
> @@ -108,8 +108,8 @@ config SPL_SEMIHOSTING
>
> config SPL_SEMIHOSTING_FALLBACK
> bool "Recover gracefully when semihosting fails in SPL"
> - depends on SPL_SEMIHOSTING && ARM64
> - select ARMV8_SPL_EXCEPTION_VECTORS
> + depends on SPL_SEMIHOSTING && (ARM64 || RISCV)
> + select ARMV8_SPL_EXCEPTION_VECTORS if ARM64
> default y
> help
> Normally, if U-Boot makes a semihosting call and no debugger is
>
The rest looks fine.
--Sean
