[PATCH 1/3] tty/serial: Add RISC-V SBI earlycon support

Anup Patel
2018-12-04T14:10:58Z

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>
---
drivers/tty/serial/Kconfig | 12 +++++++++++
drivers/tty/serial/Makefile | 1 +
drivers/tty/serial/earlycon-riscv-sbi.c | 28 +++++++++++++++++++++++++
3 files changed, 41 insertions(+)
create mode 100644 drivers/tty/serial/earlycon-riscv-sbi.c

diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index 32886c304641..287bb41ac814 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -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
diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
index daac675612df..3ce26ce08616 100644
--- a/drivers/tty/serial/Makefile
+++ b/drivers/tty/serial/Makefile
@@ -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
diff --git a/drivers/tty/serial/earlycon-riscv-sbi.c b/drivers/tty/serial/earlycon-riscv-sbi.c
new file mode 100644
index 000000000000..e1a551aae336
--- /dev/null
+++ b/drivers/tty/serial/earlycon-riscv-sbi.c
@@ -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);
--
2.17.1