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Commit d50d7269 authored by Rob Herring's avatar Rob Herring Committed by Greg Kroah-Hartman
Browse files

tty/serial: add arm/arm64 semihosting earlycon 



Add earlycon support for the arm/arm64 semihosting debug serial
interface. This allows enabling a debug console when early_params are
processed. This is based on the arm64 earlyprintk smh support and is
intended to replace it.

Signed-off-by: default avatarRob Herring <robh@kernel.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 0d3c673e

Documentation/kernel-parameters.txt

+2 −0
Original line number Diff line number Diff line
@@ -899,6 +899,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted. 
			must already be setup and configured. Options are not

			yet supported.



		smh	Use ARM semihosting calls for early console.



	earlyprintk=	[X86,SH,BLACKFIN,ARM]

			earlyprintk=vga

			earlyprintk=efi

drivers/tty/serial/Kconfig

+10 −0
Original line number Diff line number Diff line
@@ -73,6 +73,16 @@ config SERIAL_AMBA_PL011_CONSOLE 
	  your boot loader (lilo or loadlin) about how to pass options to the

	  kernel at boot time.)



config SERIAL_EARLYCON_ARM_SEMIHOST

	bool "Early console using ARM semihosting"

	depends on ARM64 || ARM

	select SERIAL_EARLYCON

	help

	  Support for early debug console using ARM semihosting. This enables

	  the console before standard serial driver is probed. This is enabled

	  with "earlycon=smh" on the kernel command line. The console is

	  enabled when early_param is processed.



config SERIAL_SB1250_DUART

	tristate "BCM1xxx on-chip DUART serial support"

	depends on SIBYTE_SB1xxx_SOC=y

drivers/tty/serial/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -6,6 +6,7 @@ obj-$(CONFIG_SERIAL_CORE) += serial_core.o 
obj-$(CONFIG_SERIAL_21285) += 21285.o



obj-$(CONFIG_SERIAL_EARLYCON) += earlycon.o

obj-$(CONFIG_SERIAL_EARLYCON_ARM_SEMIHOST) += earlycon-arm-semihost.o



# These Sparc drivers have to appear before others such as 8250

# which share ttySx minor node space.  Otherwise console device

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

0 → 100644
+61 −0
Original line number Diff line number Diff line 
/*

 * Copyright (C) 2012 ARM Ltd.

 * Author: Marc Zyngier <marc.zyngier@arm.com>

 *

 * Adapted for ARM and earlycon:

 * Copyright (C) 2014 Linaro Ltd.

 * Author: Rob Herring <robh@kernel.org>

 *

 * This program is free software: you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 as

 * published by the Free Software Foundation.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program.  If not, see <http://www.gnu.org/licenses/>.

 */

#include <linux/kernel.h>

#include <linux/console.h>

#include <linux/init.h>

#include <linux/serial_core.h>



#ifdef CONFIG_THUMB2_KERNEL

#define SEMIHOST_SWI	"0xab"

#else

#define SEMIHOST_SWI	"0x123456"

#endif



/*

 * Semihosting-based debug console

 */

static void smh_putc(struct uart_port *port, int c)

{

#ifdef CONFIG_ARM64

	asm volatile("mov  x1, %0\n"

		     "mov  x0, #3\n"

		     "hlt  0xf000\n"

		     : : "r" (&c) : "x0", "x1", "memory");

#else

	asm volatile("mov  r1, %0\n"

		     "mov  r0, #3\n"

		     "svc  " SEMIHOST_SWI "\n"

		     : : "r" (&c) : "r0", "r1", "memory");

#endif

}



static void smh_write(struct console *con, const char *s, unsigned n)

{

	struct earlycon_device *dev = con->data;

	uart_console_write(&dev->port, s, n, smh_putc);

}



int __init early_smh_setup(struct earlycon_device *device, const char *opt)

{

	device->con->write = smh_write;

	return 0;

}

EARLYCON_DECLARE(smh, early_smh_setup);