[PATCH] tty: New RISC-V SBI console driver

[Palmer Dabbelt]

From: Palmer Dabbelt <palmer@xxxxxxxxxxx>

The RISC-V ISA defines a simple console that is availiable via SBI calls
on all systems.  This patch adds a driver for this console interface
that can act as both a target for early printk and as the system
console.  The core arch code already enables the early printk support
when CONFIG_HVC_RISCV_SBI is defined.

There is one checkpatch.pl warning here: to check the MAINTAINERS file.
They're all matched by the "K: riscv" line.

Signed-off-by: Palmer Dabbelt <palmer@xxxxxxxxxxx>
---
 arch/riscv/include/asm/hvc_riscv_sbi.h | 12 ++++++
 drivers/tty/hvc/Kconfig                | 11 +++++
 drivers/tty/hvc/Makefile               |  1 +
 drivers/tty/hvc/hvc_riscv_sbi.c        | 75 ++++++++++++++++++++++++++++++++++
 4 files changed, 99 insertions(+)
 create mode 100644 arch/riscv/include/asm/hvc_riscv_sbi.h
 create mode 100644 drivers/tty/hvc/hvc_riscv_sbi.c

diff --git a/arch/riscv/include/asm/hvc_riscv_sbi.h b/arch/riscv/include/asm/hvc_riscv_sbi.h
new file mode 100644
index 000000000000..41723ed7bd97
--- /dev/null
+++ b/arch/riscv/include/asm/hvc_riscv_sbi.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _ASM_RISCV_HVC_RISCV_SBI_H
+#define _ASM_RISCV_HVC_RISCV_SBI_H
+
+/*
+ * We always support CONFIG_EARLY_PRINTK via the SBI console driver because it
+ * works well enough that there's no penalty to doing so.
+ */
+extern struct console riscv_sbi_early_console_dev __initdata;
+
+#endif
diff --git a/drivers/tty/hvc/Kconfig b/drivers/tty/hvc/Kconfig
index fec457edad14..5e267bb002af 100644
--- a/drivers/tty/hvc/Kconfig
+++ b/drivers/tty/hvc/Kconfig
@@ -97,6 +97,17 @@ config HVC_BFIN_JTAG
 	 the HVC driver.  If you don't have JTAG, then you probably don't
 	 want this option.
 
+config HVC_RISCV_SBI
+	bool "RISC-V SBI console support"
+	depends on RISCV
+	select HVC_DRIVER
+	default y
+	help
+	  This enables support for console output via RISC-V SBI calls, which
+	  is normally used only during boot to output printk.
+
+	  If you don't know what do to here, say Y.
+
 config HVCS
 	tristate "IBM Hypervisor Virtual Console Server support"
 	depends on PPC_PSERIES && HVC_CONSOLE
diff --git a/drivers/tty/hvc/Makefile b/drivers/tty/hvc/Makefile
index 0b02ec7f1dfd..83079ae000ae 100644
--- a/drivers/tty/hvc/Makefile
+++ b/drivers/tty/hvc/Makefile
@@ -11,4 +11,5 @@ obj-$(CONFIG_HVC_XEN)		+= hvc_xen.o
 obj-$(CONFIG_HVC_IUCV)		+= hvc_iucv.o
 obj-$(CONFIG_HVC_UDBG)		+= hvc_udbg.o
 obj-$(CONFIG_HVC_BFIN_JTAG)	+= hvc_bfin_jtag.o
+obj-$(CONFIG_HVC_RISCV_SBI)	+= hvc_riscv_sbi.o
 obj-$(CONFIG_HVCS)		+= hvcs.o
diff --git a/drivers/tty/hvc/hvc_riscv_sbi.c b/drivers/tty/hvc/hvc_riscv_sbi.c
new file mode 100644
index 000000000000..83ef0dcc24e0
--- /dev/null
+++ b/drivers/tty/hvc/hvc_riscv_sbi.c
@@ -0,0 +1,75 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <linux/console.h>
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/moduleparam.h>
+#include <linux/types.h>
+
+#include <asm/sbi.h>
+#include <asm/hvc_riscv_sbi.h>
+
+#include "hvc_console.h"
+
+static int hvc_sbi_tty_put(uint32_t vtermno, const char *buf, int count)
+{
+	int i;
+
+	for (i = 0; i < count; i++)
+		sbi_console_putchar(buf[i]);
+
+	return i;
+}
+
+static int hvc_sbi_tty_get(uint32_t vtermno, char *buf, int count)
+{
+	int i, c;
+
+	for (i = 0; i < count; i++) {
+		c = sbi_console_getchar();
+		if (c < 0)
+			break;
+		buf[i] = c;
+	}
+
+	return i;
+}
+
+static const struct hv_ops hvc_sbi_ops = {
+	.get_chars = hvc_sbi_tty_get,
+	.put_chars = hvc_sbi_tty_put,
+};
+
+static int __init hvc_sbi_init(void)
+{
+	return PTR_ERR_OR_ZERO(hvc_alloc(0, 0, &hvc_sbi_ops, 16));
+}
+device_initcall(hvc_sbi_init);
+
+static int __init hvc_sbi_console_init(void)
+{
+	hvc_instantiate(0, 0, &hvc_sbi_ops);
+	add_preferred_console("hvc", 0, NULL);
+
+	return 0;
+}
+console_initcall(hvc_sbi_console_init);
+
+static void sbi_console_write(struct console *co, const char *buf,
+			      unsigned int n)
+{
+	int i;
+
+	for (i = 0; i < n; ++i) {
+		if (buf[i] == '\n')
+			sbi_console_putchar('\r');
+		sbi_console_putchar(buf[i]);
+	}
+}
+
+struct console riscv_sbi_early_console_dev __initdata = {
+	.name	= "early",
+	.write	= sbi_console_write,
+	.flags	= CON_PRINTBUFFER | CON_BOOT | CON_ANYTIME,
+	.index	= -1
+};
-- 
2.13.6