From aac122ab17aaf66dab59d4ca262b6a0f67860d97 Mon Sep 17 00:00:00 2001
From: Andrew Kaster <akaster@serenityos.org>
Date: Fri, 17 Feb 2023 10:35:32 -0700
Subject: [PATCH] =?UTF-8?q?Revert=20"Kernel:=20Remove=20old=20=E2=80=98mai?=
 =?UTF-8?q?n=20id=20register=20accessor=CA=BC=20for=20Aarch64"?=
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This patch needed more review than it got.

This reverts commit 84e8d5f41842f6c3f9f613f3570f669328fe4d06.
---
 Kernel/Arch/aarch64/MainIdRegister.cpp | 19 ++++++++++++++
 Kernel/Arch/aarch64/MainIdRegister.h   | 36 ++++++++++++++++++++++++++
 Kernel/CMakeLists.txt                  |  1 +
 3 files changed, 56 insertions(+)
 create mode 100644 Kernel/Arch/aarch64/MainIdRegister.cpp
 create mode 100644 Kernel/Arch/aarch64/MainIdRegister.h

diff --git a/Kernel/Arch/aarch64/MainIdRegister.cpp b/Kernel/Arch/aarch64/MainIdRegister.cpp
new file mode 100644
index 0000000000..0ffec21116
--- /dev/null
+++ b/Kernel/Arch/aarch64/MainIdRegister.cpp
@@ -0,0 +1,19 @@
+/*
+ * Copyright (c) 2021, Nico Weber <thakis@chromium.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/Arch/aarch64/MainIdRegister.h>
+
+namespace Kernel {
+
+MainIdRegister::MainIdRegister()
+{
+    unsigned int mrs;
+    asm volatile("mrs %x0, MIDR_EL1"
+                 : "=r"(mrs));
+    m_value = mrs;
+}
+
+}
diff --git a/Kernel/Arch/aarch64/MainIdRegister.h b/Kernel/Arch/aarch64/MainIdRegister.h
new file mode 100644
index 0000000000..1b53c269d0
--- /dev/null
+++ b/Kernel/Arch/aarch64/MainIdRegister.h
@@ -0,0 +1,36 @@
+/*
+ * Copyright (c) 2021, Nico Weber <thakis@chromium.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+namespace Kernel {
+
+class MainIdRegister {
+public:
+    MainIdRegister();
+
+    enum Implementer {
+        ArmLimited = 0x41,
+    };
+    unsigned implementer() const { return (m_value >> 24) & 0xFF; }
+    unsigned variant() const { return (m_value >> 20) & 0xF; }
+    unsigned architecture() const { return (m_value >> 16) & 0xF; }
+
+    enum PartNum {
+        RaspberryPi1 = 0xB76,
+        RaspberryPi2 = 0xC07,
+        RaspberryPi3 = 0xD03,
+        RaspberryPi4 = 0xD08,
+    };
+    unsigned part_num() const { return (m_value >> 4) & 0xFFF; }
+
+    unsigned revision() const { return m_value & 0xF; }
+
+private:
+    unsigned int m_value;
+};
+
+}
diff --git a/Kernel/CMakeLists.txt b/Kernel/CMakeLists.txt
index 036c84f7d6..5a0c8d896a 100644
--- a/Kernel/CMakeLists.txt
+++ b/Kernel/CMakeLists.txt
@@ -460,6 +460,7 @@ elseif("${SERENITY_ARCH}" STREQUAL "aarch64")
         Arch/aarch64/InterruptManagement.cpp
         Arch/aarch64/Interrupts.cpp
         Arch/aarch64/kprintf.cpp
+        Arch/aarch64/MainIdRegister.cpp
         Arch/aarch64/PageDirectory.cpp
         Arch/aarch64/Panic.cpp
         Arch/aarch64/Processor.cpp