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

   1 /*
   2  * Copyright (C) 2012 ARM Ltd.
   3  * Author: Marc Zyngier <marc.zyngier@arm.com>
   4  *
   5  * Adapted for ARM and earlycon:
   6  * Copyright (C) 2014 Linaro Ltd.
   7  * Author: Rob Herring <robh@kernel.org>
   8  *
   9  * This program is free software: you can redistribute it and/or modify
  10  * it under the terms of the GNU General Public License version 2 as
  11  * published by the Free Software Foundation.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License
  19  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  20  */
  21 #include <linux/kernel.h>
  22 #include <linux/console.h>
  23 #include <linux/init.h>
  24 #include <linux/serial_core.h>
  25
  26 #ifdef CONFIG_THUMB2_KERNEL
  27 #define SEMIHOST_SWI    "0xab"
  28 #else
  29 #define SEMIHOST_SWI    "0x123456"
  30 #endif
  31
  32 /*
  33  * Semihosting-based debug console
  34  */
  35 static void smh_putc(struct uart_port *port, int c)
  36 {
  37 #ifdef CONFIG_ARM64
  38         asm volatile("mov  x1, %0\n"
  39                      "mov  x0, #3\n"
  40                      "hlt  0xf000\n"
  41                      : : "r" (&c) : "x0", "x1", "memory");
  42 #else
  43         asm volatile("mov  r1, %0\n"
  44                      "mov  r0, #3\n"
  45                      "svc  " SEMIHOST_SWI "\n"
  46                      : : "r" (&c) : "r0", "r1", "memory");
  47 #endif
  48 }
  49
  50 static void smh_write(struct console *con, const char *s, unsigned n)
  51 {
  52         struct earlycon_device *dev = con->data;
  53         uart_console_write(&dev->port, s, n, smh_putc);
  54 }
  55
  56 static int
  57 __init early_smh_setup(struct earlycon_device *device, const char *opt)
  58 {
  59         device->con->write = smh_write;
  60         return 0;
  61 }
  62 EARLYCON_DECLARE(smh, early_smh_setup);