[v2,1/1] lib: utils/serial: add semihosting support

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 <apatel@ventanamicro.com>
Signed-off-by: Kautuk Consul <kconsul@ventanamicro.com>
---
 include/sbi_utils/serial/semihosting.h |  47 +++++++
 lib/utils/serial/Kconfig               |   4 +
 lib/utils/serial/objects.mk            |   1 +
 lib/utils/serial/semihosting.c         | 175 +++++++++++++++++++++++++
 platform/generic/configs/defconfig     |   1 +
 platform/generic/platform.c            |  11 +-
 6 files changed, 238 insertions(+), 1 deletion(-)
 create mode 100644 include/sbi_utils/serial/semihosting.h
 create mode 100644 lib/utils/serial/semihosting.c

There are some more changes required from my side which got exposed
due to testing with different console=* parameters to the kernel.

I will send out a v3 with my latest changes.


On Fri, Sep 9, 2022 at 11:43 AM Kautuk Consul <kconsul@ventanamicro.com> 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 <apatel@ventanamicro.com>
> Signed-off-by: Kautuk Consul <kconsul@ventanamicro.com>
> ---
>  include/sbi_utils/serial/semihosting.h |  47 +++++++
>  lib/utils/serial/Kconfig               |   4 +
>  lib/utils/serial/objects.mk            |   1 +
>  lib/utils/serial/semihosting.c         | 175 +++++++++++++++++++++++++
>  platform/generic/configs/defconfig     |   1 +
>  platform/generic/platform.c            |  11 +-
>  6 files changed, 238 insertions(+), 1 deletion(-)
>  create mode 100644 include/sbi_utils/serial/semihosting.h
>  create mode 100644 lib/utils/serial/semihosting.c
>
> diff --git a/include/sbi_utils/serial/semihosting.h b/include/sbi_utils/serial/semihosting.h
> new file mode 100644
> index 0000000..8cc4a86
> --- /dev/null
> +++ b/include/sbi_utils/serial/semihosting.h
> @@ -0,0 +1,47 @@
> +/*
> + * SPDX-License-Identifier: BSD-2-Clause
> + *
> + * Copyright (c) 2022 Ventana Micro Systems Inc.
> + *
> + * Authors:
> + *   Anup Patel <apatel@ventanamicro.com>
> + *   Kautuk Consul <kconsul@ventanamicro.com>
> + */
> +
> +#ifndef __SERIAL_SEMIHOSTING_H__
> +#define __SERIAL_SEMIHOSTING_H__
> +
> +#include <sbi/sbi_types.h>
> +
> +/**
> + * enum semihosting_open_mode - Numeric file modes for use with semihosting_open()
> + * MODE_READ: 'r'
> + * MODE_BINARY: 'b'
> + * MODE_PLUS: '+'
> + * MODE_WRITE: 'w'
> + * MODE_APPEND: 'a'
> + *
> + * These modes represent the mode string used by fopen(3) in a form which can
> + * be passed to semihosting_open(). These do NOT correspond directly to %O_RDONLY,
> + * %O_CREAT, etc; see fopen(3) for details. In particular, @MODE_PLUS
> + * effectively results in adding %O_RDWR, and @MODE_WRITE will add %O_TRUNC.
> + * For compatibility, @MODE_BINARY should be added when opening non-text files
> + * (such as images).
> + */
> +enum semihosting_open_mode {
> +       MODE_READ       = 0x0,
> +       MODE_BINARY     = 0x1,
> +       MODE_PLUS       = 0x2,
> +       MODE_WRITE      = 0x4,
> +       MODE_APPEND     = 0x8,
> +};
> +
> +#ifdef CONFIG_SERIAL_SEMIHOSTING
> +int semihosting_init(void);
> +int semihosting_enabled(void);
> +#else
> +static inline int semihosting_init(void) { return SBI_ENODEV; }
> +static inline int semihosting_enabled(void) { return 0; }
> +#endif
> +
> +#endif
> diff --git a/lib/utils/serial/Kconfig b/lib/utils/serial/Kconfig
> index 6e425f2..da549a7 100644
> --- a/lib/utils/serial/Kconfig
> +++ b/lib/utils/serial/Kconfig
> @@ -79,4 +79,8 @@ config SERIAL_XILINX_UARTLITE
>         bool "Xilinx UART Lite support"
>         default n
>
> +config SERIAL_SEMIHOSTING
> +       bool "Semihosting support"
> +       default n
> +
>  endmenu
> diff --git a/lib/utils/serial/objects.mk b/lib/utils/serial/objects.mk
> index efb1d9e..98f3f9a 100644
> --- a/lib/utils/serial/objects.mk
> +++ b/lib/utils/serial/objects.mk
> @@ -41,3 +41,4 @@ libsbiutils-objs-$(CONFIG_SERIAL_SIFIVE) += serial/sifive-uart.o
>  libsbiutils-objs-$(CONFIG_SERIAL_LITEX) += serial/litex-uart.o
>  libsbiutils-objs-$(CONFIG_SERIAL_UART8250) += serial/uart8250.o
>  libsbiutils-objs-$(CONFIG_SERIAL_XILINX_UARTLITE) += serial/xlnx-uartlite.o
> +libsbiutils-objs-$(CONFIG_SERIAL_SEMIHOSTING) += serial/semihosting.o
> diff --git a/lib/utils/serial/semihosting.c b/lib/utils/serial/semihosting.c
> new file mode 100644
> index 0000000..57ab5ce
> --- /dev/null
> +++ b/lib/utils/serial/semihosting.c
> @@ -0,0 +1,175 @@
> +/*
> + * SPDX-License-Identifier: BSD-2-Clause
> + *
> + * Copyright (c) 2022 Ventana Micro Systems Inc.
> + *
> + * Authors:
> + *   Anup Patel <apatel@ventanamicro.com>
> + *   Kautuk Consul <kconsul@ventanamicro.com>
> + */
> +
> +#include <sbi/sbi_console.h>
> +#include <sbi/sbi_string.h>
> +#include <sbi/sbi_error.h>
> +#include <sbi_utils/serial/semihosting.h>
> +
> +#define SYSOPEN     0x01
> +#define SYSWRITEC   0x03
> +#define SYSREAD     0x06
> +#define SYSREADC    0x07
> +#define SYSERRNO       0x13
> +
> +static long semihosting_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;
> +}
> +
> +static bool _semihosting_enabled = true;
> +static bool try_semihosting = true;
> +
> +bool semihosting_enabled(void)
> +{
> +       register int ret asm ("a0") = SYSERRNO;
> +       register void *param0 asm ("a1") = NULL;
> +       unsigned long tmp = 0;
> +
> +       if (!try_semihosting)
> +               return _semihosting_enabled;
> +
> +       asm volatile (
> +               "\t.option push\n"
> +               "\t.option norvc\n"
> +
> +               "\tj _semihost_test_vector_next\n"
> +               "\t.align 4\n"
> +               "\t_semihost_test_vector:\n"
> +               "\t\tcsrr %[en], mepc\n"
> +               "\t\taddi %[en], %[en], 4\n"
> +               "\t\tcsrw mepc, %[en]\n"
> +               "\t\tadd %[en], zero, zero\n"
> +               "\t\tmret\n"
> +               "\t_semihost_test_vector_next:\n"
> +
> +               "\tla %[tmp], _semihost_test_vector\n"
> +               "\tcsrrw %[tmp], mtvec, %[tmp]\n"
> +               "\tj 1f\n"
> +               "\t.align 4\n"
> +               "\t1: slli zero, zero, 0x1f\n"
> +               "\tebreak\n"
> +               "\tsrai zero, zero, 7\n"
> +               "\tcsrw mtvec, %[tmp]\n"
> +
> +               "\t.option pop\n"
> +               : [tmp] "+r" (tmp), [en] "+r" (_semihosting_enabled),
> +                 [ret] "+r" (ret)
> +               : "r" (param0) : "memory");
> +
> +       try_semihosting = false;
> +       return _semihosting_enabled;
> +}
> +
> +static int semihosting_errno(void)
> +{
> +       long ret = semihosting_trap(SYSERRNO, NULL);
> +
> +       if (ret > 0)
> +               return -ret;
> +       return SBI_EIO;
> +}
> +
> +static int infd = SBI_ENODEV;
> +
> +static long semihosting_open(const char *fname, enum semihosting_open_mode mode)
> +{
> +       long fd;
> +       struct semihosting_open_s {
> +               const char *fname;
> +               unsigned long mode;
> +               size_t len;
> +       } open;
> +
> +       open.fname = fname;
> +       open.len = sbi_strlen(fname);
> +       open.mode = mode;
> +
> +       /* Open the file on the host */
> +       fd = semihosting_trap(SYSOPEN, &open);
> +       if (fd == -1)
> +               return semihosting_errno();
> +       return fd;
> +}
> +
> +/**
> + * struct semihosting_rdwr_s - Arguments for read and write
> + * @fd: A file descriptor returned from semihosting_open()
> + * @memp: Pointer to a buffer of memory of at least @len bytes
> + * @len: The number of bytes to read or write
> + */
> +struct semihosting_rdwr_s {
> +       long fd;
> +       void *memp;
> +       size_t len;
> +};
> +
> +static long semihosting_read(long fd, void *memp, size_t len)
> +{
> +       long ret;
> +       struct semihosting_rdwr_s read;
> +
> +       read.fd = fd;
> +       read.memp = memp;
> +       read.len = len;
> +
> +       ret = semihosting_trap(SYSREAD, &read);
> +       if (ret < 0)
> +               return semihosting_errno();
> +       return len - ret;
> +}
> +
> +/* clang-format on */
> +
> +static void semihosting_putc(char ch)
> +{
> +       semihosting_trap(SYSWRITEC, &ch);
> +}
> +
> +static int semihosting_getc(void)
> +{
> +       char ch = 0;
> +
> +       if (infd < 0)
> +               return semihosting_trap(SYSREADC, NULL);
> +
> +       semihosting_read(infd, &ch, sizeof(ch));
> +
> +       return ch;
> +}
> +
> +static struct sbi_console_device semihosting_console = {
> +       .name = "semihosting",
> +       .console_putc = semihosting_putc,
> +       .console_getc = semihosting_getc
> +};
> +
> +int semihosting_init(void)
> +{
> +       infd = semihosting_open(":tt", MODE_READ);
> +
> +       sbi_console_set_device(&semihosting_console);
> +
> +       return 0;
> +}
> diff --git a/platform/generic/configs/defconfig b/platform/generic/configs/defconfig
> index e324173..c95b7fa 100644
> --- a/platform/generic/configs/defconfig
> +++ b/platform/generic/configs/defconfig
> @@ -28,3 +28,4 @@ CONFIG_FDT_SERIAL_UART8250=y
>  CONFIG_FDT_SERIAL_XILINX_UARTLITE=y
>  CONFIG_FDT_TIMER=y
>  CONFIG_FDT_TIMER_MTIMER=y
> +CONFIG_SERIAL_SEMIHOSTING=y
> diff --git a/platform/generic/platform.c b/platform/generic/platform.c
> index cc3620f..bf51aba 100644
> --- a/platform/generic/platform.c
> +++ b/platform/generic/platform.c
> @@ -23,6 +23,7 @@
>  #include <sbi_utils/timer/fdt_timer.h>
>  #include <sbi_utils/ipi/fdt_ipi.h>
>  #include <sbi_utils/reset/fdt_reset.h>
> +#include <sbi_utils/serial/semihosting.h>
>
>  /* List of platform override modules generated at compile time */
>  extern const struct platform_override *platform_override_modules[];
> @@ -242,6 +243,14 @@ static uint64_t generic_pmu_xlate_to_mhpmevent(uint32_t event_idx,
>         return evt_val;
>  }
>
> +static int generic_console_init(void)
> +{
> +       if (semihosting_enabled())
> +               return semihosting_init();
> +       else
> +               return fdt_serial_init();
> +}
> +
>  const struct sbi_platform_operations platform_ops = {
>         .nascent_init           = generic_nascent_init,
>         .early_init             = generic_early_init,
> @@ -249,7 +258,7 @@ const struct sbi_platform_operations platform_ops = {
>         .early_exit             = generic_early_exit,
>         .final_exit             = generic_final_exit,
>         .domains_init           = generic_domains_init,
> -       .console_init           = fdt_serial_init,
> +       .console_init           = generic_console_init,
>         .irqchip_init           = fdt_irqchip_init,
>         .irqchip_exit           = fdt_irqchip_exit,
>         .ipi_init               = fdt_ipi_init,
> --
> 2.34.1
>