From 21658b9b151daeca5634e730344ba11e1e2e02c9 Mon Sep 17 00:00:00 2001
From: Gwilym Inzani <email@gwilym.dev>
Date: Mon, 27 May 2024 14:16:24 +0100
Subject: [PATCH] Revert "Remove lifetime from dma transfer handle"

---
 CHANGELOG.md                                 |  4 ---
 agb/examples/dma_effect_background_colour.rs | 10 ++++---
 agb/examples/dma_effect_background_scroll.rs |  3 ++-
 agb/examples/dma_effect_circular_window.rs   |  2 +-
 agb/src/dma.rs                               | 28 +++++++++++---------
 5 files changed, 25 insertions(+), 22 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0378cbfb..095a6e51 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,10 +11,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Added `find_colour_index_16` and `find_colour_index_256` to the `VRamManager` to find where a colour is in a palette.
 
-### Changed
-
-- `dma.hblank_transfer` is no longer `unsafe`.
-
 ## [0.20.2] - 2024/05/25
 
 ### Fixed
diff --git a/agb/examples/dma_effect_background_colour.rs b/agb/examples/dma_effect_background_colour.rs
index 7d1cfed1..f7386c59 100644
--- a/agb/examples/dma_effect_background_colour.rs
+++ b/agb/examples/dma_effect_background_colour.rs
@@ -37,10 +37,12 @@ fn main(mut gba: agb::Gba) -> ! {
         .expect("Should contain colour 0x732b");
 
     loop {
-        let _background_color_transfer = dma.hblank_transfer(
-            &vram.background_palette_colour_dma(0, background_colour_index),
-            &colours,
-        );
+        let _background_color_transfer = unsafe {
+            dma.hblank_transfer(
+                &vram.background_palette_colour_dma(0, background_colour_index),
+                &colours,
+            )
+        };
 
         vblank.wait_for_vblank();
     }
diff --git a/agb/examples/dma_effect_background_scroll.rs b/agb/examples/dma_effect_background_scroll.rs
index a74243ce..eb5cdfaa 100644
--- a/agb/examples/dma_effect_background_scroll.rs
+++ b/agb/examples/dma_effect_background_scroll.rs
@@ -34,7 +34,8 @@ fn main(mut gba: agb::Gba) -> ! {
     let mut frame = 0;
 
     loop {
-        let _x_scroll_transfer = dma.hblank_transfer(&map.x_scroll_dma(), &offsets[frame..]);
+        let _x_scroll_transfer =
+            unsafe { dma.hblank_transfer(&map.x_scroll_dma(), &offsets[frame..]) };
 
         vblank.wait_for_vblank();
         frame += 1;
diff --git a/agb/examples/dma_effect_circular_window.rs b/agb/examples/dma_effect_circular_window.rs
index cbdf8285..d98e6f60 100644
--- a/agb/examples/dma_effect_circular_window.rs
+++ b/agb/examples/dma_effect_circular_window.rs
@@ -90,7 +90,7 @@ fn main(mut gba: agb::Gba) -> ! {
         window.commit();
 
         let dma_controllable = window.win_in(WinIn::Win0).horizontal_position_dma();
-        let _transfer = dmas.dma0.hblank_transfer(&dma_controllable, &circle_poses);
+        let _transfer = unsafe { dmas.dma0.hblank_transfer(&dma_controllable, &circle_poses) };
 
         vblank.wait_for_vblank();
     }
diff --git a/agb/src/dma.rs b/agb/src/dma.rs
index 48e870db..a16fc021 100644
--- a/agb/src/dma.rs
+++ b/agb/src/dma.rs
@@ -70,14 +70,18 @@ impl Dma {
     /// drop the DmaTransferHandler return value until the next vblank interrupt to ensure that you
     /// a continuous effect.
     ///
+    /// # Safety
+    ///
+    /// While DmaTransferHandle is not dropped, the slice at `values` must not move in memory.
+    ///
     /// # Examples
     ///
     /// See the `dma_effect_*` examples in the repository to see some ways to use this.
-    pub fn hblank_transfer<T>(
-        &self,
+    pub unsafe fn hblank_transfer<'a, T>(
+        &'a self,
         location: &DmaControllable<T>,
-        values: &[T],
-    ) -> DmaTransferHandle<T>
+        values: &'a [T],
+    ) -> DmaTransferHandle<'a, T>
     where
         T: Copy,
     {
@@ -89,13 +93,10 @@ impl Dma {
 
         let n_transfers = (size_of::<T>() / 2) as u32;
 
-        self.source_addr.set(handle.data[1..].as_ptr() as u32);
+        self.source_addr.set(handle.data.as_ptr().add(1) as u32);
         self.dest_addr.set(location.memory_location as u32);
 
-        // SAFETY: by construction it is safe to write to location.memory_location
-        unsafe {
-            location.memory_location.write_volatile(values[0]);
-        }
+        location.memory_location.write_volatile(values[0]);
 
         self.ctrl_addr.set(
             (0b10 << 0x15) | // keep destination address fixed
@@ -126,15 +127,17 @@ impl<Item> DmaControllable<Item> {
     }
 }
 
-pub struct DmaTransferHandle<T>
+pub struct DmaTransferHandle<'a, T>
 where
     T: Copy,
 {
     number: usize,
     data: Pin<Box<[T]>>,
+
+    phantom: PhantomData<&'a ()>,
 }
 
-impl<T> DmaTransferHandle<T>
+impl<'a, T> DmaTransferHandle<'a, T>
 where
     T: Copy,
 {
@@ -142,11 +145,12 @@ where
         Self {
             number,
             data: Box::into_pin(data.into()),
+            phantom: PhantomData,
         }
     }
 }
 
-impl<T> Drop for DmaTransferHandle<T>
+impl<'a, T> Drop for DmaTransferHandle<'a, T>
 where
     T: Copy,
 {