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tty/serial: add arm/arm64 semihosting earlycon

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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: Rob Herring <robh@kernel.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Rob Herring 2014-04-18 17:19:58 -05:00 committed by Greg Kroah-Hartman
parent 0d3c673e78
commit d50d7269eb
4 changed files with 74 additions and 0 deletions
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2
Documentation/kernel-parameters.txt
View file

@ -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
drivers/tty/serial/Kconfig
View file

@ -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
drivers/tty/serial/Makefile
View file

@ -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
drivers/tty/serial/earlycon-arm-semihost.c Normal file
View file

@ -0,0 +1,61 @@
/*
* 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);