serial: implement riscv SBI console support

Implement a console over legacy SBI (version 0.1.0). There is a tiny ringbuffer
to simplify checking for presence and reading characters as separate steps.

Link: https://lore.barebox.org/20210927200521.7996-1-marcelo.politzer@cartesi.io
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

2 files changed, 22 insertions, 0 deletions

diff --git a/arch/riscv/cpu/core.c b/arch/riscv/cpu/core.c
index 80730c05b5..1d5902a51f 100644
--- a/arch/riscv/cpu/core.c
+++ b/arch/riscv/cpu/core.c
@@ -33,6 +33,7 @@ static int riscv_request_stack(void)
 coredevice_initcall(riscv_request_stack);
 
 static struct device_d timer_dev;
+static struct device_d serial_sbi_dev;
 
 static s64 hartid;
 
@@ -75,6 +76,17 @@ static int riscv_probe(struct device_d *parent)
 			return ret;
 	}
 
+	if (IS_ENABLED(CONFIG_SERIAL_SBI) && !serial_sbi_dev.parent) {
+		serial_sbi_dev.id = DEVICE_ID_SINGLE;
+		serial_sbi_dev.device_node = 0;
+		serial_sbi_dev.parent = parent;
+		dev_set_name(&serial_sbi_dev, "riscv-serial-sbi");
+
+		ret = platform_device_register(&serial_sbi_dev);
+		if (ret)
+			return ret;
+	}
+
 	hartid = riscv_hartid();
 	if (hartid >= 0)
 		globalvar_add_simple_uint64("hartid", &hartid, "%llu");
diff --git a/arch/riscv/lib/sbi.c b/arch/riscv/lib/sbi.c
index 45a04fb821..a57c834b41 100644
--- a/arch/riscv/lib/sbi.c
+++ b/arch/riscv/lib/sbi.c
@@ -64,3 +64,13 @@ static int sbi_init(void)
 
 }
 core_initcall(sbi_init);
+
+void sbi_console_putchar(int ch)
+{
+	sbi_ecall(SBI_EXT_0_1_CONSOLE_PUTCHAR, 0, ch, 0, 0, 0, 0, 0);
+}
+
+int sbi_console_getchar(void)
+{
+	return sbi_ecall(SBI_EXT_0_1_CONSOLE_GETCHAR, 0, 0, 0, 0, 0, 0, 0).error;
+}