drivers/tty/serial/earlycon-arm-semihost.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2012 ARM Ltd.
   4  * Author: Marc Zyngier <marc.zyngier@arm.com>
   5  *
   6  * Adapted for ARM and earlycon:
   7  * Copyright (C) 2014 Linaro Ltd.
   8  * Author: Rob Herring <robh@kernel.org>
   9  */
  10 #include <linux/kernel.h>
  11 #include <linux/console.h>
  12 #include <linux/init.h>
  13 #include <linux/serial_core.h>
  14
  15 #ifdef CONFIG_THUMB2_KERNEL
  16 #define SEMIHOST_SWI    "0xab"
  17 #else
  18 #define SEMIHOST_SWI    "0x123456"
  19 #endif
  20
  21 /*
  22  * Semihosting-based debug console
  23  */
  24 static void smh_putc(struct uart_port *port, int c)
  25 {
  26 #ifdef CONFIG_ARM64
  27         asm volatile("mov  x1, %0\n"
  28                      "mov  x0, #3\n"
  29                      "hlt  0xf000\n"
  30                      : : "r" (&c) : "x0", "x1", "memory");
  31 #else
  32         asm volatile("mov  r1, %0\n"
  33                      "mov  r0, #3\n"
  34                      "svc  " SEMIHOST_SWI "\n"
  35                      : : "r" (&c) : "r0", "r1", "memory");
  36 #endif
  37 }
  38
  39 static void smh_write(struct console *con, const char *s, unsigned n)
  40 {
  41         struct earlycon_device *dev = con->data;
  42         uart_console_write(&dev->port, s, n, smh_putc);
  43 }
  44
  45 static int
  46 __init early_smh_setup(struct earlycon_device *device, const char *opt)
  47 {
  48         device->con->write = smh_write;
  49         return 0;
  50 }
  51 EARLYCON_DECLARE(smh, early_smh_setup);