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Commit d50d7269 authored by Rob Herring's avatar Rob Herring Committed by Greg Kroah-Hartman
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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
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+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
+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
+1 −0
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@@ -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
+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);