gpu: nova-core: add DMA object struct

Since we will need to allocate lots of distinct memory chunks to be
shared between GPU and CPU, introduce a type dedicated to that. It is a
light wrapper around CoherentAllocation.

Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://lore.kernel.org/r/20250619-nova-frts-v6-13-ecf41ef99252@nvidia.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Author: Gnurou

drivers/gpu/nova-core/dma.rs

@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Simple DMA object wrapper.
+
+// To be removed when all code is used.
+#![expect(dead_code)]
+
+use core::ops::{Deref, DerefMut};
+
+use kernel::device;
+use kernel::dma::CoherentAllocation;
+use kernel::page::PAGE_SIZE;
+use kernel::prelude::*;
+
+pub(crate) struct DmaObject {
+    dma: CoherentAllocation<u8>,
+}
+
+impl DmaObject {
+    pub(crate) fn new(dev: &device::Device<device::Bound>, len: usize) -> Result<Self> {
+        let len = core::alloc::Layout::from_size_align(len, PAGE_SIZE)
+            .map_err(|_| EINVAL)?
+            .pad_to_align()
+            .size();
+        let dma = CoherentAllocation::alloc_coherent(dev, len, GFP_KERNEL | __GFP_ZERO)?;
+
+        Ok(Self { dma })
+    }
+
+    pub(crate) fn from_data(dev: &device::Device<device::Bound>, data: &[u8]) -> Result<Self> {
+        Self::new(dev, data.len()).map(|mut dma_obj| {
+            // TODO: replace with `CoherentAllocation::write()` once available.
+            // SAFETY:
+            // - `dma_obj`'s size is at least `data.len()`.
+            // - We have just created this object and there is no other user at this stage.
+            unsafe {
+                core::ptr::copy_nonoverlapping(
+                    data.as_ptr(),
+                    dma_obj.dma.start_ptr_mut(),
+                    data.len(),
+                );
+            }
+
+            dma_obj
+        })
+    }
+}
+
+impl Deref for DmaObject {
+    type Target = CoherentAllocation<u8>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.dma
+    }
+}
+
+impl DerefMut for DmaObject {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.dma
+    }
+}

drivers/gpu/nova-core/nova_core.rs

@@ -2,6 +2,7 @@
 
 //! Nova Core GPU Driver
 
+mod dma;
 mod driver;
 mod firmware;
 mod gfw;