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From:   Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
To:     Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>
Cc:     Albert Ou <aou@eecs.berkeley.edu>,
        Anup Patel <apatel@ventanamicro.com>,
        Andrew Jones <ajones@ventanamicro.com>,
        Mayuresh Chitale <mchitale@ventanamicro.com>,
        Samuel Holland <samuel.holland@sifive.com>,
        Alexandre Ghiti <alexghiti@rivosinc.com>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Subject: [PATCH 1/1] tty/serial: RISC-V SBI earlycon via DBCN extension
Date:   Wed, 15 Nov 2023 14:31:27 +0100
Message-Id: <20231115133127.107575-1-heinrich.schuchardt@canonical.com>
MIME-Version: 1.0
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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@canonical.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