linux-kernel - [PATCH 1/1] tty/serial: RISC-V SBI earlycon via DBCN extension

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Date:   Wed, 15 Nov 2023 14:31:27 +0100
From:   Heinrich Schuchardt <heinrich.schuchardt@...onical.com>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>
Cc:     Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <apatel@...tanamicro.com>,
        Andrew Jones <ajones@...tanamicro.com>,
        Mayuresh Chitale <mchitale@...tanamicro.com>,
        Samuel Holland <samuel.holland@...ive.com>,
        Alexandre Ghiti <alexghiti@...osinc.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Heinrich Schuchardt <heinrich.schuchardt@...onical.com>
Subject: [PATCH 1/1] tty/serial: RISC-V SBI earlycon via DBCN extension

Up to now an SBI based early console was limited to SBI version 0.1.
With the DBCN SBI extension we can provide an early console on systems that
have a recent SBI implementation.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@...onical.com>
---
 arch/riscv/kernel/sbi.c    | 14 ++++++++++++++
 drivers/tty/serial/Kconfig |  1 -
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
index 5a62ed1da453..6e1644a95bb7 100644
--- a/arch/riscv/kernel/sbi.c
+++ b/arch/riscv/kernel/sbi.c
@@ -195,6 +195,20 @@ static void sbi_set_power_off(void)
 	pm_power_off = sbi_shutdown;
 }
 #else
+
+/**
+ * sbi_console_putchar() - Writes given character to the console device.
+ * @ch: The data to be written to the console.
+ *
+ * Return: None
+ */
+void sbi_console_putchar(int ch)
+{
+	sbi_ecall(SBI_EXT_DBCN, SBI_EXT_DBCN_CONSOLE_WRITE_BYTE,
+		  ch, 0, 0, 0, 0, 0);
+}
+EXPORT_SYMBOL(sbi_console_putchar);
+
 static void __sbi_set_timer_v01(uint64_t stime_value)
 {
 	pr_warn("Timer extension is not available in SBI v%lu.%lu\n",
diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index 732c893c8d16..454c2a612389 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -87,7 +87,6 @@ config SERIAL_EARLYCON_SEMIHOST
 
 config SERIAL_EARLYCON_RISCV_SBI
 	bool "Early console using RISC-V SBI"
-	depends on RISCV_SBI_V01
 	select SERIAL_CORE
 	select SERIAL_CORE_CONSOLE
 	select SERIAL_EARLYCON
-- 
2.40.1