Kernel: Add UART class for aarch64

Author: https://github.com/nico
Commit: 54aabb07f9
Pull-request: https://github.com/SerenityOS/serenity/pull/10223

Kernel/Prekernel/Arch/aarch64/UART.h

@@ -0,0 +1,51 @@
+/*
+ * Copyright (c) 2021, Nico Weber <thakis@chromium.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Types.h>
+
+namespace Prekernel {
+
+struct UARTRegisters;
+
+// Abstracts the PL011 UART on a Raspberry Pi.
+// (The BCM2711 on a Raspberry Pi 4 has five PL011 UARTs; this is always the first of those.)
+class UART {
+public:
+    static UART& the();
+
+    void send(u32 c);
+    u32 receive();
+
+    void print_str(const char* s)
+    {
+        while (*s)
+            send(*s++);
+    }
+    void print_num(u32 n)
+    {
+        char buf[11];
+        int i = 0;
+        while (n) {
+            buf[i++] = (n % 10) + '0';
+            n /= 10;
+        }
+        for (i--; i >= 0; i--)
+            send(buf[i]);
+    }
+
+private:
+    UART();
+
+    void set_baud_rate(int baud_rate, int uart_frequency_in_hz);
+    void wait_until_we_can_send();
+    void wait_until_we_can_receive();
+
+    UARTRegisters volatile* m_registers;
+};
+
+}