platform: Move platform common to lib/utils.

Currently, platform/common contains platform/non-platform specific
common minimal drivers and libraries. This is helpful is all platforms
are built within opensbi framework.

Move them to lib/utils so that any external platform code also can
reuse the minimalistic drivers or other common libraries.

This patch doesn't introduce any functional changes.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Acked-by: Anup Patel <anup.patel@wdc.com>

lib/utils/serial/sifive-uart.c

@@ -0,0 +1,101 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2019 Western Digital Corporation or its affiliates.
+ *
+ * Authors:
+ *   Anup Patel <anup.patel@wdc.com>
+ */
+
+#include <sbi/riscv_io.h>
+#include <sbi/sbi_console.h>
+#include <sbi_utils/serial/sifive-uart.h>
+
+/* clang-format off */
+
+#define UART_REG_TXFIFO		0
+#define UART_REG_RXFIFO		1
+#define UART_REG_TXCTRL		2
+#define UART_REG_RXCTRL		3
+#define UART_REG_IE		4
+#define UART_REG_IP		5
+#define UART_REG_DIV		6
+
+#define UART_TXFIFO_FULL	0x80000000
+#define UART_RXFIFO_EMPTY	0x80000000
+#define UART_RXFIFO_DATA	0x000000ff
+#define UART_TXCTRL_TXEN	0x1
+#define UART_RXCTRL_RXEN	0x1
+
+/* clang-format on */
+
+static volatile void *uart_base;
+static u32 uart_in_freq;
+static u32 uart_baudrate;
+
+/**
+ * Find minimum divisor divides in_freq to max_target_hz;
+ * Based on uart driver n SiFive FSBL.
+ *
+ * f_baud = f_in / (div + 1) => div = (f_in / f_baud) - 1
+ * The nearest integer solution requires rounding up as to not exceed max_target_hz.
+ * div  = ceil(f_in / f_baud) - 1
+ *	= floor((f_in - 1 + f_baud) / f_baud) - 1
+ * This should not overflow as long as (f_in - 1 + f_baud) does not exceed
+ * 2^32 - 1, which is unlikely since we represent frequencies in kHz.
+ */
+static inline unsigned int uart_min_clk_divisor(uint64_t in_freq,
+						uint64_t max_target_hz)
+{
+	uint64_t quotient = (in_freq + max_target_hz - 1) / (max_target_hz);
+	// Avoid underflow
+	if (quotient == 0) {
+		return 0;
+	} else {
+		return quotient - 1;
+	}
+}
+
+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));
+}
+
+void sifive_uart_putc(char ch)
+{
+	while (get_reg(UART_REG_TXFIFO) & UART_TXFIFO_FULL)
+		;
+
+	set_reg(UART_REG_TXFIFO, ch);
+}
+
+int sifive_uart_getc(void)
+{
+	u32 ret = get_reg(UART_REG_RXFIFO);
+	if (!(ret & UART_RXFIFO_EMPTY))
+		return ret & UART_RXFIFO_DATA;
+	return -1;
+}
+
+int sifive_uart_init(unsigned long base, u32 in_freq, u32 baudrate)
+{
+	uart_base     = (volatile void *)base;
+	uart_in_freq  = in_freq;
+	uart_baudrate = baudrate;
+
+	/* Configure baudrate */
+	set_reg(UART_REG_DIV, uart_min_clk_divisor(in_freq, baudrate));
+	/* Disable interrupts */
+	set_reg(UART_REG_IE, 0);
+	/* Enable TX */
+	set_reg(UART_REG_TXCTRL, UART_TXCTRL_TXEN);
+	/* Enable Rx */
+	set_reg(UART_REG_RXCTRL, UART_RXCTRL_RXEN);
+
+	return 0;
+}