[PATCH 4/6] tty/serial: Add RISC-V SBI debug console based earlycon

[Anup Patel <apatel@ventanamicro.com>]

We extend the existing RISC-V SBI earlycon support to use the new
RISC-V SBI debug console extension.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
---
 drivers/tty/serial/Kconfig              |  2 +-
 drivers/tty/serial/earlycon-riscv-sbi.c | 35 ++++++++++++++++++++++---
 2 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index bdc568a4ab66..cec46091a716 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -87,7 +87,7 @@ config SERIAL_EARLYCON_SEMIHOST
 
 config SERIAL_EARLYCON_RISCV_SBI
 	bool "Early console using RISC-V SBI"
-	depends on RISCV_SBI_V01
+	depends on RISCV_SBI
 	select SERIAL_CORE
 	select SERIAL_CORE_CONSOLE
 	select SERIAL_EARLYCON
diff --git a/drivers/tty/serial/earlycon-riscv-sbi.c b/drivers/tty/serial/earlycon-riscv-sbi.c
index 27afb0b74ea7..b1da34e8d8cd 100644
--- a/drivers/tty/serial/earlycon-riscv-sbi.c
+++ b/drivers/tty/serial/earlycon-riscv-sbi.c
@@ -10,22 +10,49 @@
 #include <linux/serial_core.h>
 #include <asm/sbi.h>
 
+#ifdef CONFIG_RISCV_SBI_V01
 static void sbi_putc(struct uart_port *port, unsigned char c)
 {
 	sbi_console_putchar(c);
 }
 
-static void sbi_console_write(struct console *con,
-			      const char *s, unsigned n)
+static void sbi_0_1_console_write(struct console *con,
+				  const char *s, unsigned int n)
 {
 	struct earlycon_device *dev = con->data;
 	uart_console_write(&dev->port, s, n, sbi_putc);
 }
+#endif
+
+static void sbi_dbcn_console_write(struct console *con,
+				   const char *s, unsigned int n)
+{
+	phys_addr_t pa = __pa(s);
+
+	sbi_ecall(SBI_EXT_DBCN, SBI_EXT_DBCN_CONSOLE_WRITE,
+#ifdef CONFIG_32BIT
+		  n, pa, (u64)pa >> 32,
+#else
+		  n, pa, 0,
+#endif
+		  0, 0, 0);
+}
 
 static int __init early_sbi_setup(struct earlycon_device *device,
 				  const char *opt)
 {
-	device->con->write = sbi_console_write;
-	return 0;
+	int ret = 0;
+
+	if ((sbi_spec_version >= sbi_mk_version(2, 0)) &&
+	    (sbi_probe_extension(SBI_EXT_DBCN) > 0))
+		device->con->write = sbi_dbcn_console_write;
+	else
+#ifdef CONFIG_RISCV_SBI_V01
+		device->con->write = sbi_0_1_console_write;
+#else
+		ret = -ENODEV;
+#endif
+
+	return ret;
 }
 EARLYCON_DECLARE(sbi, early_sbi_setup);
-- 
2.34.1