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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  */
smh_putc(struct uart_port * port,int c)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 
smh_write(struct console * con,const char * s,unsigned n)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 
early_smh_setup(struct earlycon_device * device,const char * opt)56 int __init early_smh_setup(struct earlycon_device *device, const char *opt)
57 {
58 	device->con->write = smh_write;
59 	return 0;
60 }
61 EARLYCON_DECLARE(smh, early_smh_setup);
62