rust: samples: dma: set DMA mask

Set a DMA mask for the `pci::Device` in the Rust DMA sample driver.

Reviewed-by: Abdiel Janulgue <abdiel.janulgue@gmail.com>
Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20250716150354.51081-6-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Author: Danilo Krummrich

samples/rust/rust_dma.rs

@@ -4,7 +4,14 @@
 //!
 //! To make this driver probe, QEMU must be run with `-device pci-testdev`.
 
-use kernel::{bindings, device::Core, dma::CoherentAllocation, pci, prelude::*, types::ARef};
+use kernel::{
+    bindings,
+    device::Core,
+    dma::{CoherentAllocation, Device, DmaMask},
+    pci,
+    prelude::*,
+    types::ARef,
+};
 
 struct DmaSampleDriver {
     pdev: ARef<pci::Device>,
@@ -51,6 +58,11 @@ impl pci::Driver for DmaSampleDriver {
     fn probe(pdev: &pci::Device<Core>, _info: &Self::IdInfo) -> Result<Pin<KBox<Self>>> {
         dev_info!(pdev.as_ref(), "Probe DMA test driver.\n");
 
+        let mask = DmaMask::new::<64>();
+
+        // SAFETY: There are no concurrent calls to DMA allocation and mapping primitives.
+        unsafe { pdev.dma_set_mask_and_coherent(mask)? };
+
         let ca: CoherentAllocation<MyStruct> =
             CoherentAllocation::alloc_coherent(pdev.as_ref(), TEST_VALUES.len(), GFP_KERNEL)?;