lib: utils: Add LiteX UART support

Add support for the UART provided by the LiteX SoC
framework (https://github.com/enjoy-digital/litex),
based on its FDT info (described in the Linux tree at
Documentation/devicetree/bindings/serial/litex,liteuart.yaml).

Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>
Reviewed-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>

include/sbi_utils/serial/litex-uart.h

@@ -0,0 +1,17 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2021 Gabriel Somlo
+ *
+ * Authors:
+ *   Gabriel Somlo <gsomlo@gmail.com>
+ */
+
+#ifndef __SERIAL_LITEX_UART_H__
+#define __SERIAL_LITEX_UART_H__
+
+#include <sbi/sbi_types.h>
+
+int litex_uart_init(unsigned long base);
+
+#endif

lib/utils/serial/fdt_serial.c

@@ -15,6 +15,7 @@
 
 extern struct fdt_serial fdt_serial_uart8250;
 extern struct fdt_serial fdt_serial_sifive;
+extern struct fdt_serial fdt_serial_litex;
 extern struct fdt_serial fdt_serial_htif;
 extern struct fdt_serial fdt_serial_shakti;
 extern struct fdt_serial fdt_serial_gaisler;
@@ -22,6 +23,7 @@ extern struct fdt_serial fdt_serial_gaisler;
 static struct fdt_serial *serial_drivers[] = {
 	&fdt_serial_uart8250,
 	&fdt_serial_sifive,
+	&fdt_serial_litex,
 	&fdt_serial_htif,
 	&fdt_serial_shakti,
 	&fdt_serial_gaisler

lib/utils/serial/fdt_serial_litex.c

@@ -0,0 +1,39 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2021 Gabriel Somlo
+ *
+ * Authors:
+ *   Gabriel Somlo <gsomlo@gmail.com>
+ */
+
+#include <sbi/sbi_error.h>
+#include <sbi_utils/fdt/fdt_helper.h>
+#include <sbi_utils/serial/fdt_serial.h>
+#include <sbi_utils/serial/litex-uart.h>
+
+static int serial_litex_init(void *fdt, int nodeoff,
+			     const struct fdt_match *match)
+{
+	uint64_t reg_addr, reg_size;
+	int rc;
+
+	if (nodeoff < 0 || !fdt)
+		return SBI_ENODEV;
+
+	rc = fdt_get_node_addr_size(fdt, nodeoff, 0, &reg_addr, &reg_size);
+	if (rc < 0 || !reg_addr || !reg_size)
+		return SBI_ENODEV;
+
+	return litex_uart_init(reg_addr);
+}
+
+static const struct fdt_match serial_litex_match[] = {
+	{ .compatible = "litex,liteuart" },
+	{ },
+};
+
+struct fdt_serial fdt_serial_litex = {
+	.match_table = serial_litex_match,
+	.init = serial_litex_init
+};

lib/utils/serial/litex-uart.c

@@ -0,0 +1,63 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2021 Gabriel Somlo
+ *
+ * Authors:
+ *   Gabriel Somlo <gsomlo@gmail.com>
+ */
+
+#include <sbi/riscv_io.h>
+#include <sbi/sbi_console.h>
+#include <sbi_utils/serial/litex-uart.h>
+
+/* clang-format off */
+
+#define UART_REG_RXTX		0
+#define UART_REG_TXFULL		1
+#define UART_REG_RXEMPTY	2
+#define UART_REG_EV_STATUS	3
+#define UART_REG_EV_PENDING	4
+#define UART_REG_EV_ENABLE	5
+
+/* clang-format on */
+
+static volatile u32 *uart_base;
+
+static u8 get_reg(u8 reg)
+{
+	return readb(uart_base + reg);
+}
+
+static void set_reg(u8 reg, u8 val)
+{
+	writeb(val, uart_base + reg);
+}
+
+static void litex_uart_putc(char ch)
+{
+	while (get_reg(UART_REG_TXFULL));
+	set_reg(UART_REG_RXTX, ch);
+}
+
+static int litex_uart_getc(void)
+{
+	if (get_reg(UART_REG_RXEMPTY))
+		return -1;
+	else
+		return get_reg(UART_REG_RXTX);
+}
+
+static struct sbi_console_device litex_console = {
+	.name = "litex_uart",
+	.console_putc = litex_uart_putc,
+	.console_getc = litex_uart_getc
+};
+
+int litex_uart_init(unsigned long base)
+{
+	uart_base = (volatile u32 *)base;
+	set_reg(UART_REG_EV_ENABLE, 0); /* UART in polling mode: disable IRQ */
+	sbi_console_set_device(&litex_console);
+	return 0;
+}

lib/utils/serial/objects.mk

@@ -12,8 +12,10 @@ libsbiutils-objs-y += serial/fdt_serial_gaisler.o
 libsbiutils-objs-y += serial/fdt_serial_htif.o
 libsbiutils-objs-y += serial/fdt_serial_shakti.o
 libsbiutils-objs-y += serial/fdt_serial_sifive.o
+libsbiutils-objs-y += serial/fdt_serial_litex.o
 libsbiutils-objs-y += serial/fdt_serial_uart8250.o
 libsbiutils-objs-y += serial/gaisler-uart.o
 libsbiutils-objs-y += serial/shakti-uart.o
 libsbiutils-objs-y += serial/sifive-uart.o
+libsbiutils-objs-y += serial/litex-uart.o
 libsbiutils-objs-y += serial/uart8250.o