[PATCH v2 1/1] lib: utils/serial: add semihosting support
Kautuk Consul
kconsul at ventanamicro.com
Mon Sep 12 03:54:44 PDT 2022
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 at 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 at ventanamicro.com>
> Signed-off-by: Kautuk Consul <kconsul at 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 at ventanamicro.com>
> + * Kautuk Consul <kconsul at 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 at ventanamicro.com>
> + * Kautuk Consul <kconsul at 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
>
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