[DMA 6/8] More helper types & working split (#2532)

* Add helper traits to simplify DMA channel trait bounds

* Document changes

* Update doc example

* Remove clutter from MG

* Move DmaEligible down to place helper types closer

* Rename

* Include split in the MG

Author: bugadani

esp-hal/CHANGELOG.md

@@ -12,7 +12,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - ESP32-S3: Added SDMMC signals (#2556)
 - Added `set_priority` to the `DmaChannel` trait on GDMA devices (#2403, #2526)
 - Added `into_async` and `into_blocking` functions for `ParlIoTxOnly`, `ParlIoRxOnly` (#2526)
-- ESP32-C6, H2, S3: Added `split` function to the `DmaChannel` trait. (#2526)
+- ESP32-C6, H2, S3: Added `split` function to the `DmaChannel` trait. (#2526, #2532)
+- DMA: `PeripheralDmaChannel` type aliasses and `DmaChannelFor` traits to improve usability. (#2532)
 
 ### Changed
 

esp-hal/MIGRATING-0.22.md

@@ -1,6 +1,8 @@
 # Migration Guide from 0.22.x to v1.0.0-beta.0
 
-## DMA configuration changes
+## DMA changes
+
+### Configuration changes
 
 - `configure_for_async` and `configure` have been removed
 - PDMA devices (ESP32, ESP32-S2) provide no configurability
@@ -27,6 +29,76 @@
 +.with_dma(dma_channel);
 ```
 
+### Usability changes affecting applications
+
+Individual channels are no longer wrapped in `Channel`, but they implement the `DmaChannel` trait.
+This means that if you want to split them into an `rx` and a `tx` half (which is only supported on
+the H2, C6 and S3 currently), you can't move out of the channel but instead you need to call
+the `split` method.
+
+```diff
+-let tx = channel.tx;
++use esp_hal::dma::DmaChannel;
++let (rx, tx) = channel.split();
+```
+
+The `Channel` types remain available for use in peripheral drivers.
+
+It is now simpler to work with DMA channels in generic contexts. esp-hal now provides convenience
+traits and type aliasses to specify peripheral compatibility. The `ChannelCreator` types have been
+removed, further simplifying use.
+
+For example, previously you may have needed to write something like this to accept a DMA channel
+in a generic function:
+
+```rust
+fn new_foo<'d, T>(
+    dma_channel: ChannelCreator<2>, // It wasn't possible to accept a generic ChannelCreator.
+    peripheral: impl Peripheral<P = T> + 'd,
+)
+where
+    T: SomePeripheralInstance,
+    ChannelCreator<2>: DmaChannelConvert<<T as DmaEligible>::Dma>,
+{
+    let dma_channel = dma_channel.configure_for_async(false, DmaPriority::Priority0);
+
+    let driver = PeripheralDriver::new(peripheral, config).with_dma(dma_channel);
+
+    // ...
+}
+```
+
+From now on a similar, but more flexible implementation may look like:
+
+```rust
+fn new_foo<'d, T, CH>(
+    dma_channel: impl Peripheral<P = CH> + 'd,
+    peripheral: impl Peripheral<P = T> + 'd,
+)
+where
+    T: SomePeripheralInstance,
+    CH: DmaChannelFor<T>,
+{
+    // Optionally: dma_channel.set_priority(DmaPriority::Priority2);
+
+    let driver = PeripheralDriver::new(peripheral, config).with_dma(dma_channel);
+
+    // ...
+}
+```
+
+### Usability changes affecting third party peripheral drivers
+
+If you are writing a driver and need to store a channel in a structure, you can use one of the
+`ChannelFor` type aliasses.
+
+```diff
+ struct Aes<'d> {
+-    channel: ChannelTx<'d, Blocking, <AES as DmaEligible>::Dma>,
++    channel: ChannelTx<'d, Blocking, PeripheralTxChannel<AES>>,
+ }
+```
+
 ## Timer changes
 
 The low level timers, `SystemTimer` and `TimerGroup` are now "dumb". They contain no logic for operating modes or trait implementations (except the low level `Timer` trait).

esp-hal/src/aes/mod.rs

@@ -241,16 +241,16 @@ pub mod dma {
             ChannelRx,
             ChannelTx,
             DescriptorChain,
-            DmaChannelConvert,
             DmaChannelFor,
             DmaDescriptor,
             DmaPeripheral,
             DmaTransferRxTx,
+            PeripheralDmaChannel,
+            PeripheralRxChannel,
+            PeripheralTxChannel,
             ReadBuffer,
             Rx,
-            RxChannelFor,
             Tx,
-            TxChannelFor,
             WriteBuffer,
         },
         peripheral::Peripheral,
@@ -281,7 +281,7 @@ pub mod dma {
         /// The underlying [`Aes`](super::Aes) driver
         pub aes: super::Aes<'d>,
 
-        channel: Channel<'d, Blocking, DmaChannelFor<AES>>,
+        channel: Channel<'d, Blocking, PeripheralDmaChannel<AES>>,
         rx_chain: DescriptorChain,
         tx_chain: DescriptorChain,
     }
@@ -295,7 +295,7 @@ pub mod dma {
             tx_descriptors: &'static mut [DmaDescriptor],
         ) -> AesDma<'d>
         where
-            CH: DmaChannelConvert<DmaChannelFor<AES>>,
+            CH: DmaChannelFor<AES>,
         {
             let channel = Channel::new(channel.map(|ch| ch.degrade()));
             channel.runtime_ensure_compatible(&self.aes);
@@ -331,7 +331,7 @@ pub mod dma {
     }
 
     impl<'d> DmaSupportTx for AesDma<'d> {
-        type TX = ChannelTx<'d, Blocking, TxChannelFor<AES>>;
+        type TX = ChannelTx<'d, Blocking, PeripheralTxChannel<AES>>;
 
         fn tx(&mut self) -> &mut Self::TX {
             &mut self.channel.tx
@@ -343,7 +343,7 @@ pub mod dma {
     }
 
     impl<'d> DmaSupportRx for AesDma<'d> {
-        type RX = ChannelRx<'d, Blocking, RxChannelFor<AES>>;
+        type RX = ChannelRx<'d, Blocking, PeripheralRxChannel<AES>>;
 
         fn rx(&mut self) -> &mut Self::RX {
             &mut self.channel.rx

esp-hal/src/dma/gdma.rs

@@ -60,6 +60,12 @@ impl Peripheral for AnyGdmaRxChannel {
     }
 }
 
+impl DmaChannelConvert<AnyGdmaRxChannel> for AnyGdmaRxChannel {
+    fn degrade(self) -> AnyGdmaRxChannel {
+        self
+    }
+}
+
 /// An arbitrary GDMA TX channel
 pub struct AnyGdmaTxChannel(u8);
 
@@ -71,6 +77,12 @@ impl Peripheral for AnyGdmaTxChannel {
     }
 }
 
+impl DmaChannelConvert<AnyGdmaTxChannel> for AnyGdmaTxChannel {
+    fn degrade(self) -> AnyGdmaTxChannel {
+        self
+    }
+}
+
 use embassy_sync::waitqueue::AtomicWaker;
 
 static TX_WAKERS: [AtomicWaker; CHANNEL_COUNT] = [const { AtomicWaker::new() }; CHANNEL_COUNT];

esp-hal/src/dma/mod.rs

@@ -944,38 +944,6 @@ pub trait DmaEligible {
     fn dma_peripheral(&self) -> DmaPeripheral;
 }
 
-/// Helper type to get the DMA (Rx and Tx) channel for a peripheral.
-pub type DmaChannelFor<T> = <T as DmaEligible>::Dma;
-/// Helper type to get the DMA Rx channel for a peripheral.
-pub type RxChannelFor<T> = <DmaChannelFor<T> as DmaChannel>::Rx;
-/// Helper type to get the DMA Tx channel for a peripheral.
-pub type TxChannelFor<T> = <DmaChannelFor<T> as DmaChannel>::Tx;
-
-#[doc(hidden)]
-#[macro_export]
-macro_rules! impl_dma_eligible {
-    ([$dma_ch:ident] $name:ident => $dma:ident) => {
-        impl $crate::dma::DmaEligible for $crate::peripherals::$name {
-            type Dma = $dma_ch;
-
-            fn dma_peripheral(&self) -> $crate::dma::DmaPeripheral {
-                $crate::dma::DmaPeripheral::$dma
-            }
-        }
-    };
-
-    (
-        $dma_ch:ident {
-            $($(#[$cfg:meta])? $name:ident => $dma:ident,)*
-        }
-    ) => {
-        $(
-            $(#[$cfg])?
-            $crate::impl_dma_eligible!([$dma_ch] $name => $dma);
-        )*
-    };
-}
-
 #[doc(hidden)]
 #[derive(Debug)]
 pub struct DescriptorChain {
@@ -1593,6 +1561,38 @@ impl RxCircularState {
     }
 }
 
+#[doc(hidden)]
+#[macro_export]
+macro_rules! impl_dma_eligible {
+    ([$dma_ch:ident] $name:ident => $dma:ident) => {
+        impl $crate::dma::DmaEligible for $crate::peripherals::$name {
+            type Dma = $dma_ch;
+
+            fn dma_peripheral(&self) -> $crate::dma::DmaPeripheral {
+                $crate::dma::DmaPeripheral::$dma
+            }
+        }
+    };
+
+    (
+        $dma_ch:ident {
+            $($(#[$cfg:meta])? $name:ident => $dma:ident,)*
+        }
+    ) => {
+        $(
+            $(#[$cfg])?
+            $crate::impl_dma_eligible!([$dma_ch] $name => $dma);
+        )*
+    };
+}
+
+/// Helper type to get the DMA (Rx and Tx) channel for a peripheral.
+pub type PeripheralDmaChannel<T> = <T as DmaEligible>::Dma;
+/// Helper type to get the DMA Rx channel for a peripheral.
+pub type PeripheralRxChannel<T> = <PeripheralDmaChannel<T> as DmaChannel>::Rx;
+/// Helper type to get the DMA Tx channel for a peripheral.
+pub type PeripheralTxChannel<T> = <PeripheralDmaChannel<T> as DmaChannel>::Tx;
+
 #[doc(hidden)]
 pub trait DmaRxChannel:
     RxRegisterAccess + InterruptAccess<DmaRxInterrupt> + Peripheral<P = Self>
@@ -1647,7 +1647,7 @@ pub trait DmaChannelExt: DmaChannel {
     note = "Not all channels are useable with all peripherals"
 )]
 #[doc(hidden)]
-pub trait DmaChannelConvert<DEG>: DmaChannel {
+pub trait DmaChannelConvert<DEG> {
     fn degrade(self) -> DEG;
 }
 
@@ -1657,6 +1657,94 @@ impl<DEG: DmaChannel> DmaChannelConvert<DEG> for DEG {
     }
 }
 
+/// Trait implemented for DMA channels that are compatible with a particular
+/// peripheral.
+///
+/// You can use this in places where a peripheral driver would expect a
+/// `DmaChannel` implementation.
+#[cfg_attr(pdma, doc = "")]
+#[cfg_attr(
+    pdma,
+    doc = "Note that using mismatching channels (e.g. trying to use `spi2channel` with SPI3) may compile, but will panic in runtime."
+)]
+#[cfg_attr(pdma, doc = "")]
+/// ## Example
+///
+/// The following example demonstrates how this trait can be used to only accept
+/// types compatible with a specific peripheral.
+///
+/// ```rust,no_run
+#[doc = crate::before_snippet!()]
+/// use esp_hal::spi::master::{Spi, SpiDma, Config, Instance as SpiInstance};
+/// use esp_hal::dma::DmaChannelFor;
+/// use esp_hal::peripheral::Peripheral;
+/// use esp_hal::Blocking;
+/// use esp_hal::dma::Dma;
+///
+/// fn configures_spi_dma<'d, S, CH>(
+///     spi: Spi<'d, Blocking, S>,
+///     channel: impl Peripheral<P = CH> + 'd,
+/// ) -> SpiDma<'d, Blocking, S>
+/// where
+///     S: SpiInstance,
+///     CH: DmaChannelFor<S> + 'd,
+///  {
+///     spi.with_dma(channel)
+/// }
+///
+/// let dma = Dma::new(peripherals.DMA);
+#[cfg_attr(pdma, doc = "let dma_channel = dma.spi2channel;")]
+#[cfg_attr(gdma, doc = "let dma_channel = dma.channel0;")]
+#[doc = ""]
+/// let spi = Spi::new_with_config(
+///     peripherals.SPI2,
+///     Config::default(),
+/// );
+///
+/// let spi_dma = configures_spi_dma(spi, dma_channel);
+/// # }
+/// ```
+pub trait DmaChannelFor<P: DmaEligible>:
+    DmaChannel + DmaChannelConvert<PeripheralDmaChannel<P>>
+{
+}
+impl<P, CH> DmaChannelFor<P> for CH
+where
+    P: DmaEligible,
+    CH: DmaChannel + DmaChannelConvert<PeripheralDmaChannel<P>>,
+{
+}
+
+/// Trait implemented for the RX half of split DMA channels that are compatible
+/// with a particular peripheral. Accepts complete DMA channels or split halves.
+///
+/// This trait is similar in use to [`DmaChannelFor`].
+///
+/// You can use this in places where a peripheral driver would expect a
+/// `DmaRxChannel` implementation.
+pub trait RxChannelFor<P: DmaEligible>: DmaChannelConvert<PeripheralRxChannel<P>> {}
+impl<P, RX> RxChannelFor<P> for RX
+where
+    P: DmaEligible,
+    RX: DmaChannelConvert<PeripheralRxChannel<P>>,
+{
+}
+
+/// Trait implemented for the TX half of split DMA channels that are compatible
+/// with a particular peripheral. Accepts complete DMA channels or split halves.
+///
+/// This trait is similar in use to [`DmaChannelFor`].
+///
+/// You can use this in places where a peripheral driver would expect a
+/// `DmaTxChannel` implementation.
+pub trait TxChannelFor<PER: DmaEligible>: DmaChannelConvert<PeripheralTxChannel<PER>> {}
+impl<P, TX> TxChannelFor<P> for TX
+where
+    P: DmaEligible,
+    TX: DmaChannelConvert<PeripheralTxChannel<P>>,
+{
+}
+
 /// The functions here are not meant to be used outside the HAL
 #[doc(hidden)]
 pub trait Rx: crate::private::Sealed {