Remove lifetime from dma transfer handle (#712)

The lifetime here is pointless since we copy the data anyway. And this
makes a bunch of stuff not unsafe any more which is really nice.

- [x] Changelog updated / no changelog update needed

CHANGELOG.md

@@ -11,6 +11,10 @@ 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

agb/examples/dma_effect_background_colour.rs

@@ -37,12 +37,10 @@ fn main(mut gba: agb::Gba) -> ! {
         .expect("Should contain colour 0x732b");
 
     loop {
-        let _background_color_transfer = unsafe {
-            dma.hblank_transfer(
+        let _background_color_transfer = dma.hblank_transfer(
             &vram.background_palette_colour_dma(0, background_colour_index),
             &colours,
-            )
-        };
+        );
 
         vblank.wait_for_vblank();
     }

agb/examples/dma_effect_background_scroll.rs

@@ -34,8 +34,7 @@ fn main(mut gba: agb::Gba) -> ! {
     let mut frame = 0;
 
     loop {
-        let _x_scroll_transfer =
-            unsafe { dma.hblank_transfer(&map.x_scroll_dma(), &offsets[frame..]) };
+        let _x_scroll_transfer = dma.hblank_transfer(&map.x_scroll_dma(), &offsets[frame..]);
 
         vblank.wait_for_vblank();
         frame += 1;

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 = unsafe { dmas.dma0.hblank_transfer(&dma_controllable, &circle_poses) };
+        let _transfer = dmas.dma0.hblank_transfer(&dma_controllable, &circle_poses);
 
         vblank.wait_for_vblank();
     }

agb/src/dma.rs

@@ -70,18 +70,14 @@ 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 unsafe fn hblank_transfer<'a, T>(
-        &'a self,
+    pub fn hblank_transfer<T>(
+        &self,
         location: &DmaControllable<T>,
-        values: &'a [T],
-    ) -> DmaTransferHandle<'a, T>
+        values: &[T],
+    ) -> DmaTransferHandle<T>
     where
         T: Copy,
     {
@@ -93,10 +89,13 @@ impl Dma {
 
         let n_transfers = (size_of::<T>() / 2) as u32;
 
-        self.source_addr.set(handle.data.as_ptr().add(1) as u32);
+        self.source_addr.set(handle.data[1..].as_ptr() 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]);
+        }
 
         self.ctrl_addr.set(
             (0b10 << 0x15) | // keep destination address fixed
@@ -127,17 +126,15 @@ impl<Item> DmaControllable<Item> {
     }
 }
 
-pub struct DmaTransferHandle<'a, T>
+pub struct DmaTransferHandle<T>
 where
     T: Copy,
 {
     number: usize,
     data: Pin<Box<[T]>>,
-
-    phantom: PhantomData<&'a ()>,
 }
 
-impl<'a, T> DmaTransferHandle<'a, T>
+impl<T> DmaTransferHandle<T>
 where
     T: Copy,
 {
@@ -145,12 +142,11 @@ where
         Self {
             number,
             data: Box::into_pin(data.into()),
-            phantom: PhantomData,
         }
     }
 }
 
-impl<'a, T> Drop for DmaTransferHandle<'a, T>
+impl<T> Drop for DmaTransferHandle<T>
 where
     T: Copy,
 {