From 15c55dc0cdb68db82c80f3804c4ca62eb9f3ace6 Mon Sep 17 00:00:00 2001
From: Berkus Decker <berkus+github@metta.systems>
Date: Sun, 24 Feb 2019 01:49:42 +0200
Subject: [PATCH] [wip] mmu refactor for Phil-Opps code

---
 src/arch/aarch64/mmu.rs | 63 ++++++++++++++++++++++++++++++++++++++---
 1 file changed, 59 insertions(+), 4 deletions(-)

diff --git a/src/arch/aarch64/mmu.rs b/src/arch/aarch64/mmu.rs
index bfb9973..701681d 100644
--- a/src/arch/aarch64/mmu.rs
+++ b/src/arch/aarch64/mmu.rs
@@ -27,6 +27,7 @@
 //! [ARMv8 memory addressing](https://static.docs.arm.com/100940/0100/armv8_a_address%20translation_100940_0100_en.pdf)
 
 use crate::println;
+use core::marker::PhantomData;
 use cortex_a::{barrier, regs::*};
 use register::register_bitfields;
 
@@ -109,19 +110,73 @@ impl BaseAddr for [u64; 512] {
 
 const NUM_ENTRIES_4KIB: usize = 512;
 
+struct Entry(u64);
+
+impl Entry {
+    pub fn is_unused(&self) -> bool {
+        self.0 == 0
+    }
+
+    pub fn set_unused(&mut self) {
+        self.0 = 0;
+    }
+}
+
+// Levels
+trait TableLevel {}
+
+enum Level0 {}
+enum Level1 {}
+enum Level2 {}
+enum Level3 {}
+
+impl TableLevel for Level0 {}
+impl TableLevel for Level1 {}
+impl TableLevel for Level2 {}
+impl TableLevel for Level3 {}
+
+// Levels for nested tables
+trait HierarchicalLevel: TableLevel {
+    type NextLevel: TableLevel;
+}
+
+impl HierarchicalLevel for Level0 {
+    type NextLevel = Level1;
+}
+impl HierarchicalLevel for Level1 {
+    type NextLevel = Level2;
+}
+impl HierarchicalLevel for Level2 {
+    type NextLevel = Level3;
+}
+
 // We need a wrapper struct here so that we can make use of the align attribute.
 #[repr(C)]
 #[repr(align(4096))]
-struct PageTable {
-    entries: [u64; NUM_ENTRIES_4KIB],
+struct PageTable<L: TableLevel> {
+    entries: [Entry; NUM_ENTRIES_4KIB],
+    level: PhantomData<L>,
 }
 
-static mut LVL2_TABLE: PageTable = PageTable {
+impl<L> PageTable<L>
+where
+    L: TableLevel,
+{
+    pub fn zero(&mut self) {
+        for entry in self.entries.iter_mut() {
+            entry.set_unused();
+        }
+    }
+}
+
+static mut LVL2_TABLE: PageTable<Level2> = PageTable {
     entries: [0; NUM_ENTRIES_4KIB],
+    level: PhantomData<Level2>,
 };
 
-static mut SINGLE_LVL3_TABLE: PageTable = PageTable {
+static mut SINGLE_LVL3_TABLE: PageTable<Level3> = PageTable {
     entries: [0; NUM_ENTRIES_4KIB],
+    level: PhantomData<Level3>,
 };
 
 /// Set up identity mapped page tables for the first 1 gigabyte of address