rust: dma: add Coherent:init() and Coherent::init_with_attrs()

Analogous to Coherent::zeroed() and Coherent::zeroed_with_attrs(), add
Coherent:init() and Coherent::init_with_attrs() which both take an impl
Init<T, E> argument initializing the DMA coherent memory.

Compared to CoherentInit, Coherent::init() is a one-shot constructor
that runs an Init closure and immediately exposes the DMA handle,
whereas CoherentInit is a multi-stage initializer that provides safe
&mut T access by withholding the DMA address until converted to
Coherent.

Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://patch.msgid.link/20260320194626.36263-6-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs
index 5b41603cee2e62dff0671c70d379d5ccc31a8aa2..be44ec99af5f78dbd05965de40790a647c8d8f6b 100644 (file)
--- a/rust/kernel/dma.rs
+++ b/rust/kernel/dma.rs
@@ -715,6 +715,44 @@ impl<T: AsBytes + FromBytes> Coherent<T> {
         Self::zeroed_with_attrs(dev, gfp_flags, Attrs(0))
     }
 
+    /// Same as [`Coherent::zeroed_with_attrs`], but instead of a zero-initialization the memory is
+    /// initialized with `init`.
+    pub fn init_with_attrs<E>(
+        dev: &device::Device<Bound>,
+        gfp_flags: kernel::alloc::Flags,
+        dma_attrs: Attrs,
+        init: impl Init<T, E>,
+    ) -> Result<Self>
+    where
+        Error: From<E>,
+    {
+        let dmem = Self::alloc_with_attrs(dev, gfp_flags, dma_attrs)?;
+        let ptr = dmem.as_mut_ptr();
+
+        // SAFETY:
+        // - `ptr` is valid, properly aligned, and points to exclusively owned memory.
+        // - If `__init` fails, `self` is dropped, which safely frees the underlying `Coherent`'s
+        //   DMA memory. `T: AsBytes + FromBytes` ensures there are no complex `Drop` requirements
+        //   we are bypassing.
+        unsafe { init.__init(ptr)? };
+
+        Ok(dmem)
+    }
+
+    /// Same as [`Coherent::zeroed`], but instead of a zero-initialization the memory is initialized
+    /// with `init`.
+    #[inline]
+    pub fn init<E>(
+        dev: &device::Device<Bound>,
+        gfp_flags: kernel::alloc::Flags,
+        init: impl Init<T, E>,
+    ) -> Result<Self>
+    where
+        Error: From<E>,
+    {
+        Self::init_with_attrs(dev, gfp_flags, Attrs(0), init)
+    }
+
     /// Allocates a region of `[T; len]` of coherent memory.
     fn alloc_slice_with_attrs(
         dev: &device::Device<Bound>,