rust: dma: update to keyworded index projection syntax

Demonstrate the preferred syntax of index projection in DMA documentation
and examples. A few `[i]?` cases are converted to demonstrate the new
variant.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Gary Guo <gary@garyguo.net>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patch.msgid.link/20260602-projection-syntax-rework-v2-4-6989470f5440@garyguo.net
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: nbdd0121

rust/kernel/dma.rs

@@ -1152,8 +1152,8 @@ unsafe impl Sync for CoherentHandle {}
 /// unsafe impl kernel::transmute::AsBytes for MyStruct{};
 ///
 /// # fn test(alloc: &kernel::dma::Coherent<[MyStruct]>) -> Result {
-/// let whole = kernel::dma_read!(alloc, [2]?);
-/// let field = kernel::dma_read!(alloc, [1]?.field);
+/// let whole = kernel::dma_read!(alloc, [try: 2]);
+/// let field = kernel::dma_read!(alloc, [panic: 1].field);
 /// # Ok::<(), Error>(()) }
 /// ```
 #[macro_export]
@@ -1189,8 +1189,8 @@ macro_rules! dma_read {
 /// unsafe impl kernel::transmute::AsBytes for MyStruct{};
 ///
 /// # fn test(alloc: &kernel::dma::Coherent<[MyStruct]>) -> Result {
-/// kernel::dma_write!(alloc, [2]?.member, 0xf);
-/// kernel::dma_write!(alloc, [1]?, MyStruct { member: 0xf });
+/// kernel::dma_write!(alloc, [try: 2].member, 0xf);
+/// kernel::dma_write!(alloc, [panic: 1], MyStruct { member: 0xf });
 /// # Ok::<(), Error>(()) }
 /// ```
 #[macro_export]

samples/rust/rust_dma.rs

@@ -73,7 +73,7 @@ impl pci::Driver for DmaSampleDriver {
                 Coherent::zeroed_slice(pdev.as_ref(), TEST_VALUES.len(), GFP_KERNEL)?;
 
             for (i, value) in TEST_VALUES.into_iter().enumerate() {
-                kernel::dma_write!(ca, [i]?, MyStruct::new(value.0, value.1));
+                kernel::dma_write!(ca, [try: i], MyStruct::new(value.0, value.1));
             }
 
             let size = 4 * page::PAGE_SIZE;
@@ -91,16 +91,14 @@ impl pci::Driver for DmaSampleDriver {
 }
 
 impl DmaSampleDriver {
-    fn check_dma(&self) -> Result {
+    fn check_dma(&self) {
         for (i, value) in TEST_VALUES.into_iter().enumerate() {
-            let val0 = kernel::dma_read!(self.ca, [i]?.h);
-            let val1 = kernel::dma_read!(self.ca, [i]?.b);
+            let val0 = kernel::dma_read!(self.ca, [panic: i].h);
+            let val1 = kernel::dma_read!(self.ca, [panic: i].b);
 
             assert_eq!(val0, value.0);
             assert_eq!(val1, value.1);
         }
-
-        Ok(())
     }
 }
 
@@ -109,7 +107,7 @@ impl PinnedDrop for DmaSampleDriver {
     fn drop(self: Pin<&mut Self>) {
         dev_info!(self.pdev, "Unload DMA test driver.\n");
 
-        assert!(self.check_dma().is_ok());
+        self.check_dma();
 
         for (i, entry) in self.sgt.iter().enumerate() {
             dev_info!(