lib: utils/serial: Add support for Gaisler APBUART

This patch adds support for the UART used by the NOEL-V processor.

Cobham Gaisler's NOEL-V RISC-V processor IP is available under GPL
and commercial license and is described in more detail at
https://www.gaisler.com/noelv.

Signed-off-by: Daniel Cederman <cederman@gaisler.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

lib/utils/serial/gaisler-uart.c

@@ -0,0 +1,86 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2021 Cobham Gaisler AB.
+ *
+ * Authors:
+ *   Daniel Cederman <cederman@gaisler.com>
+ */
+
+#include <sbi/riscv_io.h>
+#include <sbi/sbi_console.h>
+#include <sbi_utils/serial/gaisler-uart.h>
+
+/* clang-format off */
+
+#define UART_REG_DATA		0
+#define UART_REG_STATUS		1
+#define UART_REG_CTRL		2
+#define UART_REG_SCALER		3
+
+#define UART_DATA_DATA		0x000000ff
+#define UART_STATUS_FIFOFULL	0x00000200
+#define UART_STATUS_DATAREADY	0x00000001
+
+#define UART_CTRL_DB		(1<<11)
+#define UART_CTRL_FL		(1<<6)
+#define UART_CTRL_TE		(1<<1)
+#define UART_CTRL_RE		(1<<0)
+
+/* clang-format on */
+
+static volatile void *uart_base;
+
+static u32 get_reg(u32 num)
+{
+	return readl(uart_base + (num * 0x4));
+}
+
+static void set_reg(u32 num, u32 val)
+{
+	writel(val, uart_base + (num * 0x4));
+}
+
+static void gaisler_uart_putc(char ch)
+{
+	while (get_reg(UART_REG_STATUS) & UART_STATUS_FIFOFULL)
+		;
+
+	set_reg(UART_REG_DATA, ch);
+}
+
+static int gaisler_uart_getc(void)
+{
+	u32 ret = get_reg(UART_REG_STATUS);
+	if (!(ret & UART_STATUS_DATAREADY))
+		return -1;
+	return get_reg(UART_REG_DATA) & UART_DATA_DATA;
+}
+
+static struct sbi_console_device gaisler_console = {
+	.name	      = "gaisler_uart",
+	.console_putc = gaisler_uart_putc,
+	.console_getc = gaisler_uart_getc
+};
+
+int gaisler_uart_init(unsigned long base, u32 in_freq, u32 baudrate)
+{
+	u32 ctrl;
+
+	uart_base = (volatile void *)base;
+
+	/* Configure baudrate */
+	if (in_freq)
+		set_reg(UART_REG_SCALER, in_freq / (baudrate * 8 + 7));
+
+	ctrl = get_reg(UART_REG_CTRL);
+	/* Preserve debug mode and flow control */
+	ctrl &= (UART_CTRL_DB | UART_CTRL_FL);
+	/* Enable TX and RX */
+	ctrl |= UART_CTRL_TE | UART_CTRL_RE;
+	set_reg(UART_REG_CTRL, ctrl);
+
+	sbi_console_set_device(&gaisler_console);
+
+	return 0;
+}