3 files changed, 48 insertions, 29 deletions

diff --git a/embassy-stm32/src/dma/bdma.rs b/embassy-stm32/src/dma/bdma.rs
index b4c77757e..e06ce8c36 100644
--- a/embassy-stm32/src/dma/bdma.rs
+++ b/embassy-stm32/src/dma/bdma.rs
@@ -89,7 +89,8 @@ pac::dma_channels! {
     ($channel_peri:ident, $dma_peri:ident, bdma, $channel_num:expr, $dmamux:tt) => {
         impl crate::dma::sealed::Channel for crate::peripherals::$channel_peri {
 
-            unsafe fn start_write<W: Word>(&mut self, request: Request, buf: &[W], reg_addr: *mut W) {
+            unsafe fn start_write<W: Word>(&mut self, request: Request, buf: *const[W], reg_addr: *mut W) {
+                let (ptr, len) = super::slice_ptr_parts(buf);
                 low_level_api::start_transfer(
                     pac::$dma_peri,
                     $channel_num,
@@ -97,8 +98,8 @@ pac::dma_channels! {
                     request,
                     vals::Dir::FROMMEMORY,
                     reg_addr as *const u32,
-                    buf.as_ptr() as *mut u32,
-                    buf.len(),
+                    ptr as *mut u32,
+                    len,
                     true,
                     vals::Size::from(W::bits()),
                     #[cfg(dmamux)]
@@ -129,7 +130,8 @@ pac::dma_channels! {
                 )
             }
 
-            unsafe fn start_read<W: Word>(&mut self, request: Request, reg_addr: *mut W, buf: &mut [W]) {
+            unsafe fn start_read<W: Word>(&mut self, request: Request, reg_addr: *const W, buf: *mut [W]) {
+                let (ptr, len) = super::slice_ptr_parts_mut(buf);
                 low_level_api::start_transfer(
                     pac::$dma_peri,
                     $channel_num,
@@ -137,8 +139,8 @@ pac::dma_channels! {
                     request,
                     vals::Dir::FROMPERIPHERAL,
                     reg_addr as *const u32,
-                    buf.as_ptr() as *mut u32,
-                    buf.len(),
+                    ptr as *mut u32,
+                    len,
                     true,
                     vals::Size::from(W::bits()),
                     #[cfg(dmamux)]
diff --git a/embassy-stm32/src/dma/dma.rs b/embassy-stm32/src/dma/dma.rs
index efe4d1d9d..8e48bb26f 100644
--- a/embassy-stm32/src/dma/dma.rs
+++ b/embassy-stm32/src/dma/dma.rs
@@ -84,15 +84,16 @@ pub(crate) unsafe fn init() {
 pac::dma_channels! {
     ($channel_peri:ident, $dma_peri:ident, dma, $channel_num:expr, $dmamux:tt) => {
         impl crate::dma::sealed::Channel for crate::peripherals::$channel_peri {
-            unsafe fn start_write<W: Word>(&mut self, request: Request, buf: &[W], reg_addr: *mut W) {
+            unsafe fn start_write<W: Word>(&mut self, request: Request, buf: *const [W], reg_addr: *mut W) {
+                let (ptr, len) = super::slice_ptr_parts(buf);
                 low_level_api::start_transfer(
                     pac::$dma_peri,
                     $channel_num,
                     request,
                     vals::Dir::MEMORYTOPERIPHERAL,
                     reg_addr as *const u32,
-                    buf.as_ptr() as *mut u32,
-                    buf.len(),
+                    ptr as *mut u32,
+                    len,
                     true,
                     vals::Size::from(W::bits()),
                     #[cfg(dmamux)]
@@ -121,15 +122,16 @@ pac::dma_channels! {
                 )
             }
 
-            unsafe fn start_read<W: Word>(&mut self, request: Request, reg_addr: *mut W, buf: &mut [W]) {
+            unsafe fn start_read<W: Word>(&mut self, request: Request, reg_addr: *const W, buf: *mut [W]) {
+                let (ptr, len) = super::slice_ptr_parts_mut(buf);
                 low_level_api::start_transfer(
                     pac::$dma_peri,
                     $channel_num,
                     request,
                     vals::Dir::PERIPHERALTOMEMORY,
                     reg_addr as *const u32,
-                    buf.as_ptr() as *mut u32,
-                    buf.len(),
+                    ptr as *mut u32,
+                    len,
                     true,
                     vals::Size::from(W::bits()),
                     #[cfg(dmamux)]
diff --git a/embassy-stm32/src/dma/mod.rs b/embassy-stm32/src/dma/mod.rs
index accc55653..b7067a9c4 100644
--- a/embassy-stm32/src/dma/mod.rs
+++ b/embassy-stm32/src/dma/mod.rs
@@ -10,6 +10,7 @@ pub use dmamux::*;
 
 use core::future::Future;
 use core::marker::PhantomData;
+use core::mem;
 use core::pin::Pin;
 use core::task::Waker;
 use core::task::{Context, Poll};
@@ -36,12 +37,13 @@ pub(crate) mod sealed {
         /// Starts this channel for writing a stream of words.
         ///
         /// Safety:
+        /// - `buf` must point to a valid buffer for DMA reading.
         /// - `buf` must be alive for the entire duration of the DMA transfer.
         /// - `reg_addr` must be a valid peripheral register address to write to.
         unsafe fn start_write<W: super::Word>(
             &mut self,
             request: Request,
-            buf: &[W],
+            buf: *const [W],
             reg_addr: *mut W,
         );
 
@@ -60,13 +62,14 @@ pub(crate) mod sealed {
         /// Starts this channel for reading a stream of words.
         ///
         /// Safety:
+        /// - `buf` must point to a valid buffer for DMA writing.
         /// - `buf` must be alive for the entire duration of the DMA transfer.
-        /// - `reg_addr` must be a valid peripheral register address to write to.
+        /// - `reg_addr` must be a valid peripheral register address to read from.
         unsafe fn start_read<W: super::Word>(
             &mut self,
             request: Request,
-            reg_addr: *mut W,
-            buf: &mut [W],
+            reg_addr: *const W,
+            buf: *mut [W],
         );
 
         /// Requests the channel to stop.
@@ -132,10 +135,7 @@ mod transfers {
 
         unsafe { channel.start_read::<W>(request, reg_addr, buf) };
 
-        Transfer {
-            channel,
-            _phantom: PhantomData,
-        }
+        Transfer::new(channel)
     }
 
     #[allow(unused)]
@@ -150,10 +150,7 @@ mod transfers {
 
         unsafe { channel.start_write::<W>(request, buf, reg_addr) };
 
-        Transfer {
-            channel,
-            _phantom: PhantomData,
-        }
+        Transfer::new(channel)
     }
 
     #[allow(unused)]
@@ -168,17 +165,24 @@ mod transfers {
 
         unsafe { channel.start_write_repeated::<W>(request, repeated, count, reg_addr) };
 
-        Transfer {
-            channel,
-            _phantom: PhantomData,
-        }
+        Transfer::new(channel)
     }
 
-    struct Transfer<'a, C: Channel> {
+    pub(crate) struct Transfer<'a, C: Channel> {
         channel: C,
         _phantom: PhantomData<&'a mut C>,
     }
 
+    impl<'a, C: Channel> Transfer<'a, C> {
+        pub(crate) fn new(channel: impl Unborrow<Target = C> + 'a) -> Self {
+            unborrow!(channel);
+            Self {
+                channel,
+                _phantom: PhantomData,
+            }
+        }
+    }
+
     impl<'a, C: Channel> Drop for Transfer<'a, C> {
         fn drop(&mut self) {
             self.channel.request_stop();
@@ -221,3 +225,14 @@ pub(crate) unsafe fn init() {
     #[cfg(dmamux)]
     dmamux::init();
 }
+
+// TODO: replace transmutes with core::ptr::metadata once it's stable
+#[allow(unused)]
+pub(crate) fn slice_ptr_parts<T>(slice: *const [T]) -> (usize, usize) {
+    unsafe { mem::transmute(slice) }
+}
+
+#[allow(unused)]
+pub(crate) fn slice_ptr_parts_mut<T>(slice: *mut [T]) -> (usize, usize) {
+    unsafe { mem::transmute(slice) }
+}