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tty/serial: Add RISC-V SBI earlycon support 

In RISC-V, the M-mode runtime firmware provide SBI calls for
debug prints. This patch adds earlycon support using RISC-V
SBI console calls. To enable it, just pass "earlycon=sbi" in
kernel parameters.

Signed-off-by: Anup Patel <anup@brainfault.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Palmer Dabbelt <palmer@sifive.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
This commit is contained in:
Anup Patel 2018-12-04 19:25:05 +05:30 committed by Palmer Dabbelt
parent 801009424e
commit 27de1f541f
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3 changed files with 41 additions and 0 deletions
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12
drivers/tty/serial/Kconfig
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@ -85,6 +85,18 @@ config SERIAL_EARLYCON_ARM_SEMIHOST
with "earlycon=smh" on the kernel command line. The console is
enabled when early_param is processed.
config SERIAL_EARLYCON_RISCV_SBI
bool "Early console using RISC-V SBI"
depends on RISCV
select SERIAL_CORE
select SERIAL_CORE_CONSOLE
select SERIAL_EARLYCON
help
Support for early debug console using RISC-V SBI. This enables
the console before standard serial driver is probed. This is enabled
with "earlycon=sbi" 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

@ -7,6 +7,7 @@ obj-$(CONFIG_SERIAL_CORE) += serial_core.o
obj-$(CONFIG_SERIAL_EARLYCON) += earlycon.o
obj-$(CONFIG_SERIAL_EARLYCON_ARM_SEMIHOST) += earlycon-arm-semihost.o
obj-$(CONFIG_SERIAL_EARLYCON_RISCV_SBI) += earlycon-riscv-sbi.o
# These Sparc drivers have to appear before others such as 8250
# which share ttySx minor node space. Otherwise console device

28
drivers/tty/serial/earlycon-riscv-sbi.c Normal file
View File

@ -0,0 +1,28 @@
// SPDX-License-Identifier: GPL-2.0
/*
* RISC-V SBI based earlycon
*
* Copyright (C) 2018 Anup Patel <anup@brainfault.org>
*/
#include <linux/kernel.h>
#include <linux/console.h>
#include <linux/init.h>
#include <linux/serial_core.h>
#include <asm/sbi.h>
static void sbi_console_write(struct console *con,
const char *s, unsigned int n)
{
int i;
for (i = 0; i < n; ++i)
sbi_console_putchar(s[i]);
}
static int __init early_sbi_setup(struct earlycon_device *device,
const char *opt)
{
device->con->write = sbi_console_write;
return 0;
}
EARLYCON_DECLARE(sbi, early_sbi_setup);