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[84.248.220.251]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-5498ae4465fsm1921728e87.26.2025.03.11.10.50.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 11 Mar 2025 10:50:05 -0700 (PDT) From: Abdiel Janulgue To: rust-for-linux@vger.kernel.org, daniel.almeida@collabora.com, dakr@kernel.org, robin.murphy@arm.com, aliceryhl@google.com Cc: Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?UTF-8?q?Bj=C3=B6rn=20Roy=20Baron?= , Benno Lossin , Andreas Hindborg , Trevor Gross , Valentin Obst , linux-kernel@vger.kernel.org (open list), Christoph Hellwig , Marek Szyprowski , airlied@redhat.com, iommu@lists.linux.dev (open list:DMA MAPPING HELPERS), Abdiel Janulgue Subject: [PATCH v14 11/11] rust: dma: add as_slice/write functions for CoherentAllocation Date: Tue, 11 Mar 2025 19:48:07 +0200 Message-ID: <20250311174930.2348813-12-abdiel.janulgue@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20250311174930.2348813-1-abdiel.janulgue@gmail.com> References: <20250311174930.2348813-1-abdiel.janulgue@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Add unsafe accessors for the region for reading or writing large blocks of data. Signed-off-by: Abdiel Janulgue --- rust/kernel/dma.rs | 87 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 87 insertions(+) diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs index d0c6569cfc70..514fbb27c607 100644 --- a/rust/kernel/dma.rs +++ b/rust/kernel/dma.rs @@ -253,6 +253,93 @@ 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) -> 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