lib: utils: serial: Initial commit of xlnx-uartlite

Initial commit of the xlnx-uartlite device and FDT support. This was
tested by running OpenSBI on a modified QEMU virt machine using the
xlnx-uartlite for serial.

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup@brainfault.org>

lib/utils/serial/xlnx-uartlite.c

@@ -0,0 +1,67 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2022 Western Digital Corporation or its affiliates.
+ *
+ * Authors:
+ *   Alistair Francis <alistair.francis@wdc.com>
+ */
+
+#include <sbi/riscv_io.h>
+#include <sbi/sbi_console.h>
+#include <sbi_utils/serial/xlnx_uartlite.h>
+
+/* clang-format off */
+
+#define UART_RX_OFFSET		0x00
+#define UART_TX_OFFSET		0x04
+#define UART_STATUS_OFFSET	0x08
+# define UART_STATUS_RXVALID	0x01
+# define UART_STATUS_RXFULL	0x02
+# define UART_STATUS_TXEMPTY	0x04
+# define UART_STATUS_TXFULL	0x08
+# define UART_STATUS_IE	0x10
+# define UART_STATUS_OVERRUN	0x20
+# define UART_STATUS_FRAME	0x40
+# define UART_STATUS_PARITY	0x80
+#define UART_CTRL_OFFSET	0x0C
+# define UART_CTRL_RST_TX	0x01
+# define UART_CTRL_RST_RX	0x02
+# define UART_CTRL_IE		0x10
+
+/* clang-format on */
+
+static volatile char *xlnx_uartlite_base;
+
+static void xlnx_uartlite_putc(char ch)
+{
+	while((readb(xlnx_uartlite_base + UART_STATUS_OFFSET) & UART_STATUS_TXFULL))
+		;
+
+	writeb(ch, xlnx_uartlite_base + UART_TX_OFFSET);
+}
+
+static int xlnx_uartlite_getc(void)
+{
+	u16 status = readb(xlnx_uartlite_base + UART_STATUS_OFFSET);
+
+	if (status & UART_STATUS_RXVALID)
+		return readb(xlnx_uartlite_base + UART_RX_OFFSET);
+
+	return -1;
+}
+
+static struct sbi_console_device xlnx_uartlite_console = {
+	.name = "xlnx-uartlite",
+	.console_putc = xlnx_uartlite_putc,
+	.console_getc = xlnx_uartlite_getc
+};
+
+int xlnx_uartlite_init(unsigned long base)
+{
+	xlnx_uartlite_base = (volatile char *)base;
+
+	sbi_console_set_device(&xlnx_uartlite_console);
+
+	return 0;
+}