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Message-ID: <20250326201230.3193329-4-abdiel.janulgue@gmail.com>
Date: Wed, 26 Mar 2025 22:11:44 +0200
From: Abdiel Janulgue <abdiel.janulgue@...il.com>
To: a.hindborg@...nel.org,
ojeda@...nel.org
Cc: Danilo Krummrich <dakr@...nel.org>,
Daniel Almeida <daniel.almeida@...labora.com>,
Robin Murphy <robin.murphy@....com>,
Alex Gaynor <alex.gaynor@...il.com>,
Boqun Feng <boqun.feng@...il.com>,
Gary Guo <gary@...yguo.net>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>,
Benno Lossin <benno.lossin@...ton.me>,
Alice Ryhl <aliceryhl@...gle.com>,
Trevor Gross <tmgross@...ch.edu>,
rust-for-linux@...r.kernel.org (open list:DMA MAPPING HELPERS DEVICE DRIVER API [RUST]),
Marek Szyprowski <m.szyprowski@...sung.com>,
iommu@...ts.linux.dev (open list:DMA MAPPING HELPERS),
linux-kernel@...r.kernel.org (open list),
Abdiel Janulgue <abdiel.janulgue@...il.com>
Subject: [PATCH 3/3] rust: dma: add as_slice/write functions for CoherentAllocation
Add unsafe accessors for the region for reading or writing large
blocks of data.
Reviewed-by: Andreas Hindborg <a.hindborg@...nel.org>
Signed-off-by: Abdiel Janulgue <abdiel.janulgue@...il.com>
---
rust/kernel/dma.rs | 87 ++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 87 insertions(+)
diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs
index 24a6f10370c4..24025ec602ff 100644
--- a/rust/kernel/dma.rs
+++ b/rust/kernel/dma.rs
@@ -218,6 +218,93 @@ pub fn dma_handle(&self) -> bindings::dma_addr_t {
self.dma_handle
}
+ /// Returns the data from the region starting from `offset` as a slice.
+ /// `offset` and `count` are in units of `T`, not the number of bytes.
+ ///
+ /// Due to the safety requirements of slice, the caller should consider that the region could
+ /// be modified by the device at anytime. For ringbuffer type of r/w access or use-cases where
+ /// the pointer to the live data is needed, `start_ptr()` or `start_ptr_mut()` could be
+ /// used instead.
+ ///
+ /// # Safety
+ ///
+ /// * Callers must ensure that no hardware operations that involve the buffer are currently
+ /// taking place while the returned slice is live.
+ /// * Callers must ensure that this call does not race with a write to the same region while
+ /// while the returned slice is live.
+ pub unsafe fn as_slice(&self, offset: usize, count: usize) -> Result<&[T]> {
+ let end = offset.checked_add(count).ok_or(EOVERFLOW)?;
+ if end >= self.count {
+ return Err(EINVAL);
+ }
+ // SAFETY:
+ // - The pointer is valid due to type invariant on `CoherentAllocation`,
+ // we've just checked that the range and index is within bounds. The immutability of the
+ // of data is also guaranteed by the safety requirements of the function.
+ // - `offset` can't overflow since it is smaller than `self.count` and we've checked
+ // that `self.count` won't overflow early in the constructor.
+ Ok(unsafe { core::slice::from_raw_parts(self.cpu_addr.add(offset), count) })
+ }
+
+ /// Performs the same functionality as [`CoherentAllocation::as_slice`], except that a mutable
+ /// slice is returned.
+ ///
+ /// # Safety
+ ///
+ /// * Callers must ensure that no hardware operations that involve the buffer are currently
+ /// taking place while the returned slice is live.
+ /// * Callers must ensure that this call does not race with a read or write to the same region
+ /// while the returned slice is live.
+ pub unsafe fn as_slice_mut(&self, offset: usize, count: usize) -> Result<&mut [T]> {
+ let end = offset.checked_add(count).ok_or(EOVERFLOW)?;
+ if end >= self.count {
+ return Err(EINVAL);
+ }
+ // SAFETY:
+ // - The pointer is valid due to type invariant on `CoherentAllocation`,
+ // we've just checked that the range and index is within bounds. The immutability of the
+ // of data is also guaranteed by the safety requirements of the function.
+ // - `offset` can't overflow since it is smaller than `self.count` and we've checked
+ // that `self.count` won't overflow early in the constructor.
+ Ok(unsafe { core::slice::from_raw_parts_mut(self.cpu_addr.add(offset), count) })
+ }
+
+ /// Writes data to the region starting from `offset`. `offset` is in units of `T`, not the
+ /// number of bytes.
+ ///
+ /// # Safety
+ ///
+ /// * Callers must ensure that no hardware operations that involve the buffer overlaps with
+ /// this write.
+ /// * Callers must ensure that this call does not race with a read or write to the same region
+ /// that overlaps with this write.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// # fn test(alloc: &mut kernel::dma::CoherentAllocation<u8>) -> Result {
+ /// let somedata: [u8; 4] = [0xf; 4];
+ /// let buf: &[u8] = &somedata;
+ /// // SAFETY: No hw operation on the device and no other r/w access to the region at this point.
+ /// unsafe { alloc.write(buf, 0)?; }
+ /// # Ok::<(), Error>(()) }
+ /// ```
+ pub unsafe fn write(&self, src: &[T], offset: usize) -> Result {
+ let end = offset.checked_add(src.len()).ok_or(EOVERFLOW)?;
+ if end >= self.count {
+ return Err(EINVAL);
+ }
+ // SAFETY:
+ // - The pointer is valid due to type invariant on `CoherentAllocation`
+ // and we've just checked that the range and index is within bounds.
+ // - `offset` can't overflow since it is smaller than `self.count` and we've checked
+ // that `self.count` won't overflow early in the constructor.
+ unsafe {
+ core::ptr::copy_nonoverlapping(src.as_ptr(), self.cpu_addr.add(offset), src.len())
+ };
+ Ok(())
+ }
+
/// Returns a pointer to an element from the region with bounds checking. `offset` is in
/// units of `T`, not the number of bytes.
///
--
2.43.0
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