Kernel: Improve the aarch64 kernel source files disk layout

Kernel/Arch/aarch64/RPi/Mailbox.h

@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) 2021, Nico Weber <thakis@chromium.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Types.h>
+
+namespace Prekernel {
+
+// Can exchange mailbox messages with the Raspberry Pi's VideoCore chip.
+// https://github.com/raspberrypi/firmware/wiki/Mailbox-property-interface
+class Mailbox {
+public:
+    // Base class for Mailbox messages. Implemented in subsystems that use Mailbox.
+    class Message {
+    protected:
+        Message(u32 tag, u32 arguments_size);
+
+    private:
+        u32 m_tag;
+        u32 m_arguments_size;
+        u32 m_command_tag;
+    };
+
+    // Must be at the beginning of every command message queue
+    class MessageHeader {
+    public:
+        MessageHeader();
+
+        u32 queue_size() { return m_message_queue_size; }
+        void set_queue_size(u32 size) { m_message_queue_size = size; }
+        bool success() const;
+
+    private:
+        u32 m_message_queue_size;
+        u32 m_command_tag;
+    };
+
+    // Must be at the end of every command message queue
+    class MessageTail {
+    private:
+        u32 m_empty_tag = 0;
+    };
+
+    static Mailbox& the();
+
+    // Sends message queue to VideoCore
+    bool send_queue(void* queue, u32 queue_size) const;
+};
+
+}