feat: custom dma configuration using RegisterUpdaters struct

See this PR comment:
https://github.com/embassy-rs/embassy/pull/3923#issuecomment-2889283939

3 files changed, 51 insertions, 7 deletions

diff --git a/embassy-stm32/src/dma/gpdma/linked_list.rs b/embassy-stm32/src/dma/gpdma/linked_list.rs
index a95e5590e..76381def3 100644
--- a/embassy-stm32/src/dma/gpdma/linked_list.rs
+++ b/embassy-stm32/src/dma/gpdma/linked_list.rs
@@ -4,6 +4,7 @@
 use stm32_metapac::gpdma::regs;
 use stm32_metapac::gpdma::vals::Dreq;
 
+use super::RegisterUpdaters;
 use crate::dma::word::{Word, WordSize};
 use crate::dma::{Dir, Request};
 
@@ -41,7 +42,12 @@ pub struct LinearItem {
 
 impl LinearItem {
     /// Create a new read DMA transfer (peripheral to memory).
-    pub unsafe fn new_read<'d, W: Word>(request: Request, peri_addr: *mut W, buf: &'d mut [W]) -> Self {
+    pub unsafe fn new_read<'d, W: Word>(
+        request: Request,
+        peri_addr: *mut W,
+        buf: &'d mut [W],
+        register_updaters: &RegisterUpdaters,
+    ) -> Self {
         Self::new_inner(
             request,
             Dir::PeripheralToMemory,
@@ -51,11 +57,17 @@ impl LinearItem {
             true,
             W::size(),
             W::size(),
+            register_updaters,
         )
     }
 
     /// Create a new write DMA transfer (memory to peripheral).
-    pub unsafe fn new_write<'d, MW: Word, PW: Word>(request: Request, buf: &'d [MW], peri_addr: *mut PW) -> Self {
+    pub unsafe fn new_write<'d, MW: Word, PW: Word>(
+        request: Request,
+        buf: &'d [MW],
+        peri_addr: *mut PW,
+        register_updaters: &RegisterUpdaters,
+    ) -> Self {
         Self::new_inner(
             request,
             Dir::MemoryToPeripheral,
@@ -65,6 +77,7 @@ impl LinearItem {
             true,
             MW::size(),
             PW::size(),
+            register_updaters,
         )
     }
 
@@ -77,6 +90,7 @@ impl LinearItem {
         incr_mem: bool,
         data_size: WordSize,
         dst_size: WordSize,
+        register_updaters: &RegisterUpdaters,
     ) -> Self {
         // BNDT is specified as bytes, not as number of transfers.
         let Ok(bndt) = (mem_len * data_size.bytes()).try_into() else {
@@ -91,6 +105,7 @@ impl LinearItem {
         tr1.set_ddw(dst_size.into());
         tr1.set_sinc(dir == Dir::MemoryToPeripheral && incr_mem);
         tr1.set_dinc(dir == Dir::PeripheralToMemory && incr_mem);
+        (register_updaters.tr1)(&mut tr1);
 
         let mut tr2 = regs::ChTr2(0);
         tr2.set_dreq(match dir {
@@ -98,6 +113,7 @@ impl LinearItem {
             Dir::PeripheralToMemory => Dreq::SOURCE_PERIPHERAL,
         });
         tr2.set_reqsel(request);
+        (register_updaters.tr2)(&mut tr2);
 
         let (sar, dar) = match dir {
             Dir::MemoryToPeripheral => (mem_addr as _, peri_addr as _),
diff --git a/embassy-stm32/src/dma/gpdma/mod.rs b/embassy-stm32/src/dma/gpdma/mod.rs
index 604db2852..58f93ffb0 100644
--- a/embassy-stm32/src/dma/gpdma/mod.rs
+++ b/embassy-stm32/src/dma/gpdma/mod.rs
@@ -73,6 +73,28 @@ impl Default for TransferOptions {
     }
 }
 
+/// GPDMA linked-list item register updater functions.
+#[derive(Debug, Copy, Clone)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+pub struct RegisterUpdaters {
+    /// Function used to overwrite transfer register 1.
+    pub tr1: fn(&mut pac::gpdma::regs::ChTr1),
+    /// Function used to overwrite transfer register 2.
+    pub tr2: fn(&mut pac::gpdma::regs::ChTr2),
+    /// Function used to overwrite transfer register 3.
+    pub tr3: fn(&mut pac::gpdma::regs::ChTr3),
+}
+
+impl Default for RegisterUpdaters {
+    fn default() -> Self {
+        Self {
+            tr1: |_| {},
+            tr2: |_| {},
+            tr3: |_| {},
+        }
+    }
+}
+
 impl From<WordSize> for vals::Dw {
     fn from(raw: WordSize) -> Self {
         match raw {
diff --git a/embassy-stm32/src/dma/gpdma/ringbuffered.rs b/embassy-stm32/src/dma/gpdma/ringbuffered.rs
index c74c7bd2b..dfc031627 100644
--- a/embassy-stm32/src/dma/gpdma/ringbuffered.rs
+++ b/embassy-stm32/src/dma/gpdma/ringbuffered.rs
@@ -8,7 +8,7 @@ use core::task::Waker;
 
 use embassy_hal_internal::Peri;
 
-use super::{AnyChannel, TransferOptions, STATE};
+use super::{AnyChannel, RegisterUpdaters, TransferOptions, STATE};
 use crate::dma::gpdma::linked_list::{LinearItem, RunMode, Table};
 use crate::dma::ringbuffer::{DmaCtrl, Error, ReadableDmaRingBuffer, WritableDmaRingBuffer};
 use crate::dma::word::Word;
@@ -52,6 +52,7 @@ pub struct ReadableRingBuffer<'a, W: Word> {
     channel: Peri<'a, AnyChannel>,
     ringbuf: ReadableDmaRingBuffer<'a, W>,
     table: Table<2>,
+    options: TransferOptions,
 }
 
 impl<'a, W: Word> ReadableRingBuffer<'a, W> {
@@ -64,6 +65,7 @@ impl<'a, W: Word> ReadableRingBuffer<'a, W> {
         peri_addr: *mut W,
         buffer: &'a mut [W],
         options: TransferOptions,
+        register_updaters: RegisterUpdaters,
     ) -> Self {
         let channel: Peri<'a, AnyChannel> = channel.into();
 
@@ -72,8 +74,8 @@ impl<'a, W: Word> ReadableRingBuffer<'a, W> {
         assert_eq!(half_len * 2, buffer.len());
 
         let items = [
-            LinearItem::new_read(request, peri_addr, &mut buffer[..half_len]),
-            LinearItem::new_read(request, peri_addr, &mut buffer[half_len..]),
+            LinearItem::new_read(request, peri_addr, &mut buffer[..half_len], &register_updaters),
+            LinearItem::new_read(request, peri_addr, &mut buffer[half_len..], &register_updaters),
         ];
         let table = Table::new(items);
 
@@ -84,6 +86,7 @@ impl<'a, W: Word> ReadableRingBuffer<'a, W> {
             channel,
             ringbuf: ReadableDmaRingBuffer::new(buffer),
             table,
+            options,
         }
     }
 
@@ -211,6 +214,7 @@ pub struct WritableRingBuffer<'a, W: Word> {
     channel: Peri<'a, AnyChannel>,
     ringbuf: WritableDmaRingBuffer<'a, W>,
     table: Table<2>,
+    options: TransferOptions,
 }
 
 impl<'a, W: Word> WritableRingBuffer<'a, W> {
@@ -221,6 +225,7 @@ impl<'a, W: Word> WritableRingBuffer<'a, W> {
         peri_addr: *mut W,
         buffer: &'a mut [W],
         options: TransferOptions,
+        register_updaters: RegisterUpdaters,
     ) -> Self {
         let channel: Peri<'a, AnyChannel> = channel.into();
 
@@ -229,8 +234,8 @@ impl<'a, W: Word> WritableRingBuffer<'a, W> {
         assert_eq!(half_len * 2, buffer.len());
 
         let items = [
-            LinearItem::new_write(request, &mut buffer[..half_len], peri_addr),
-            LinearItem::new_write(request, &mut buffer[half_len..], peri_addr),
+            LinearItem::new_write(request, &mut buffer[..half_len], peri_addr, &register_updaters),
+            LinearItem::new_write(request, &mut buffer[half_len..], peri_addr, &register_updaters),
         ];
         let table = Table::new(items);
 
@@ -241,6 +246,7 @@ impl<'a, W: Word> WritableRingBuffer<'a, W> {
             channel,
             ringbuf: WritableDmaRingBuffer::new(buffer),
             table,
+            options,
         };
 
         this