linux-kernel - [PATCH v3 3/4] nova-core: Simplify `DmaObject::from

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Message-ID: <20251104193756.57726-3-delcastillodelarosadaniel@gmail.com>
Date: Tue,  4 Nov 2025 20:37:50 +0100
From: Daniel del Castillo <delcastillodelarosadaniel@...il.com>
To: Danilo Krummrich <dakr@...nel.org>,
	Alexandre Courbot <acourbot@...dia.com>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>
Cc: nouveau@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org,
	Boqun Feng <boqun.feng@...il.com>,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <lossin@...nel.org>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Trevor Gross <tmgross@...ch.edu>,
	rust-for-linux@...r.kernel.org,
	Daniel del Castillo <delcastillodelarosadaniel@...il.com>
Subject: [PATCH v3 3/4] nova-core: Simplify `DmaObject::from_data` in nova-core/dma.rs

This patch solves one of the existing mentions of COHA, a task
in the Nova task list about improving the `CoherentAllocation` API.
It uses the `write` method from `CoherentAllocation`.

Signed-off-by: Daniel del Castillo <delcastillodelarosadaniel@...il.com>

---

V1 -> V2: Split previous patch into two. One per reference to COHA.
          Added more details in Safety comment. Let me know your thoughts
          Kept the original map to avoid a temporary variable

V2 -> V3: Fixed compilation error.
---
 drivers/gpu/nova-core/dma.rs | 19 +++++--------------
 1 file changed, 5 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/nova-core/dma.rs b/drivers/gpu/nova-core/dma.rs
index 94f44bcfd748..9acbe2e4d4e5 100644
--- a/drivers/gpu/nova-core/dma.rs
+++ b/drivers/gpu/nova-core/dma.rs
@@ -25,20 +25,11 @@ pub(crate) fn new(dev: &device::Device<device::Bound>, len: usize) -> Result<Sel
     }
 
     pub(crate) fn from_data(dev: &device::Device<device::Bound>, data: &[u8]) -> Result<Self> {
-        Self::new(dev, data.len()).map(|mut dma_obj| {
-            // TODO[COHA]: 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
+        Self::new(dev, data.len()).and_then(|mut dma_obj| {
+            // SAFETY: We have just allocated the DMA memory, we are the only users and
+            // we haven't made the device aware of the handle yet.
+            unsafe { dma_obj.write(data, 0)? }
+            Ok(dma_obj)
         })
     }
 }
-- 
2.51.2