[PATCH 2/3] riscv: SBI as the interface for the early console

[Jinglin Wen]

Use the SBI interface as the early console output interface
for the RISC-V platform.

Signed-off-by: Jinglin Wen <jinglin.wen@xxxxxxxxxxxx>
---
 drivers/tty/hvc/Kconfig         | 12 ++++++++++++
 drivers/tty/hvc/hvc_riscv_sbi.c | 29 +++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/drivers/tty/hvc/Kconfig b/drivers/tty/hvc/Kconfig
index c2a4e88b328f..48658d2b700c 100644
--- a/drivers/tty/hvc/Kconfig
+++ b/drivers/tty/hvc/Kconfig
@@ -118,6 +118,18 @@ config HVC_RISCV_SBI
 
 	  If you don't know what do to here, say N.
 
+config RISCV_EARLY_CONSOLE_SBI
+	bool "Use SBI as the interface for RISC-V early console"
+	depends on RISCV
+	help
+	  Choose 'Y' to use the SBI interface as the early console
+	  output interface for the RISC-V platform.
+
+	  This configuration is a temporary setup for debugging
+	  purposes during the boot process to address issues as
+	  early as possible. It should not be enabled in production
+	  kernel.
+
 config HVCS
 	tristate "IBM Hypervisor Virtual Console Server support"
 	depends on PPC_PSERIES && HVC_CONSOLE
diff --git a/drivers/tty/hvc/hvc_riscv_sbi.c b/drivers/tty/hvc/hvc_riscv_sbi.c
index cede8a572594..6686dcf62853 100644
--- a/drivers/tty/hvc/hvc_riscv_sbi.c
+++ b/drivers/tty/hvc/hvc_riscv_sbi.c
@@ -12,6 +12,7 @@
 #include <linux/types.h>
 
 #include <asm/sbi.h>
+#include <asm/early_console.h>
 
 #include "hvc_console.h"
 
@@ -81,3 +82,31 @@ static int __init hvc_sbi_init(void)
 	return 0;
 }
 device_initcall(hvc_sbi_init);
+
+#ifdef CONFIG_RISCV_EARLY_CONSOLE_SBI
+static ssize_t (*sbi_early_putc_common)(uint32_t vtermno, const u8 *buf, size_t count);
+
+static void sbi_early_putc(char c)
+{
+	unsigned int termno = 0;
+	int count = -1;
+
+	if (c == '\n')
+		sbi_early_putc('\r');
+
+	do {
+		count = sbi_early_putc_common(termno, &c, 1);
+	} while (count == 0 || count == -EAGAIN);
+}
+
+void __init hvc_sbi_early_init(void (**putc)(char c))
+{
+	if (sbi_debug_console_available)
+		sbi_early_putc_common = hvc_sbi_dbcn_tty_put;
+	else if (IS_ENABLED(CONFIG_RISCV_SBI_V01))
+		sbi_early_putc_common = hvc_sbi_tty_put;
+
+	if (sbi_early_putc_common)
+		*putc = sbi_early_putc;
+}
+#endif
-- 
2.25.1