Allow users to create DMA Preparations (#2455)

Co-authored-by: Dominic Fischer <git@dominicfischer.me>

esp-hal/CHANGELOG.md

@@ -37,6 +37,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Circular DMA transfers now correctly error, `available` returns `Result<usize,DmaError>` now (#2409)
 - Interrupt listen/unlisten/clear functions now accept any type that converts into `EnumSet` (i.e. single interrupt flags). (#2442)
 - SPI interrupt listening is now only available in Blocking mode. The `set_interrupt_handler` is available via `InterruptConfigurable` (#2442)
+- Allow users to create DMA `Preparation`s (#2455) 
 
 ### Fixed
 

esp-hal/src/dma/buffers.rs

@@ -7,11 +7,12 @@ use crate::soc::is_slice_in_psram;
 
 /// Holds all the information needed to configure a DMA channel for a transfer.
 pub struct Preparation {
-    pub(super) start: *mut DmaDescriptor,
+    /// The descriptor the DMA will start from.
+    pub start: *mut DmaDescriptor,
 
-    /// block size for PSRAM transfers
+    /// Block size for PSRAM transfers
     #[cfg_attr(not(esp32s3), allow(dead_code))]
-    pub(super) block_size: Option<DmaBufBlkSize>,
+    pub block_size: Option<DmaBufBlkSize>,
 
     /// Specifies whether descriptor linked list specified in `start` conforms
     /// to the alignment requirements required to enable burst transfers.
@@ -22,7 +23,7 @@ pub struct Preparation {
     /// There are no additional alignment requirements for TX burst transfers,
     /// but RX transfers require all descriptors to have buffer pointers and
     /// sizes that are a multiple of 4 (word aligned).
-    pub(super) is_burstable: bool,
+    pub is_burstable: bool,
 
     /// Configures the "check owner" feature of the DMA channel.
     ///
@@ -50,7 +51,7 @@ pub struct Preparation {
     ///
     /// Note: If the DMA channel doesn't support the provided option,
     /// preparation will fail.
-    pub(super) check_owner: Option<bool>,
+    pub check_owner: Option<bool>,
 }
 
 /// [DmaTxBuffer] is a DMA descriptor + memory combo that can be used for