From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0023B1A5B8B; Thu, 28 Aug 2025 13:33:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756388020; cv=none; b=pWB2bLwZBY+QiGyXdmtNVMzDU1IxdlDKTsFWHJ3aCFT1FjVzspJFMTbZKkBxhlHk/iKoCRDCHuU+9Xm5LT58VuKArpCpPcse+9FJnaSjWXkqFzlNI1t09bwCTiKrXoMG747qtWX4o7PwCu2vr49seXjq9xmIt0CD9mX+olKR0QM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756388020; c=relaxed/simple; bh=AvZ7MAaja1vU90oIimXqqhaRqe3btMk1ANyYmRTsYac=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=KhmuPx8LZHfblezHlv0bCWUX1wosoph05HltdY2ggt9QOmtE2n+JBcSp+CfNkUimhoDka+Aox6fgDNtZLD5SNUrP0YhmYcMVOivuXg2NTVXuA0UQT7muwVyLqTe8KuoexvPvVbSbSQpQcp45Nl+CIyvRkTQS16/iXs2QMD5714U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SMVrYIV/; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="SMVrYIV/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D8624C4CEF5; Thu, 28 Aug 2025 13:33:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1756388019; bh=AvZ7MAaja1vU90oIimXqqhaRqe3btMk1ANyYmRTsYac=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=SMVrYIV/ij41z7MWnpB63VSrkEBLKoCAvsw+nR26v35J5uJ4SSypC1L/pvInGiMV5 Y+lkSYrFC6rU5aeacEb4FcPBod06YUjkz79RCekbdSNjMVr2gZ/H5CEyYQhxv/iVtY E910wjMajmmaCPcK52m6gojq6C4AXs/4MH8cJrneQVvR76cVTzXsBLyMmqzyUGfsTg 9K89OfmiI2ot8+SvkEtMBm8cbeRQc3RYDeFU76Fxamu0w3n/Q/d1CxjNUmt1rSQH/J MGZWgKydvwdZraeP9DykuZ7Ido60gnGDW7eYbAqyuyb61Z0GYRIokoBhheBUuyB/tq tb6q6p6uC6dyw== From: Danilo Krummrich To: akpm@linux-foundation.org, ojeda@kernel.org, alex.gaynor@gmail.com, boqun.feng@gmail.com, gary@garyguo.net, bjorn3_gh@protonmail.com, lossin@kernel.org, a.hindborg@kernel.org, aliceryhl@google.com, tmgross@umich.edu, abdiel.janulgue@gmail.com, acourbot@nvidia.com, jgg@ziepe.ca, lyude@redhat.com, robin.murphy@arm.com, daniel.almeida@collabora.com Cc: rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, Danilo Krummrich Subject: [PATCH v4 1/5] rust: dma: implement DataDirection Date: Thu, 28 Aug 2025 15:32:14 +0200 Message-ID: <20250828133323.53311-2-dakr@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20250828133323.53311-1-dakr@kernel.org> References: <20250828133323.53311-1-dakr@kernel.org> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Add the `DataDirection` struct, a newtype wrapper around the C `enum dma_data_direction`. This provides a type-safe Rust interface for specifying the direction of DMA transfers. Reviewed-by: Alice Ryhl Reviewed-by: Alexandre Courbot Reviewed-by: Daniel Almeida Reviewed-by: Lyude Paul Signed-off-by: Danilo Krummrich --- rust/bindings/bindings_helper.h | 1 + rust/kernel/dma.rs | 68 +++++++++++++++++++++++++++++++++ 2 files changed, 69 insertions(+) diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h index 0e140e07758b..c2cc52ee9945 100644 --- a/rust/bindings/bindings_helper.h +++ b/rust/bindings/bindings_helper.h @@ -47,6 +47,7 @@ #include #include #include +#include #include #include #include diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs index 2bc8ab51ec28..27b25f041f32 100644 --- a/rust/kernel/dma.rs +++ b/rust/kernel/dma.rs @@ -244,6 +244,74 @@ pub mod attrs { pub const DMA_ATTR_PRIVILEGED: Attrs = Attrs(bindings::DMA_ATTR_PRIVILEGED); } +/// DMA data direction. +/// +/// Corresponds to the C [`enum dma_data_direction`]. +/// +/// [`enum dma_data_direction`]: srctree/include/linux/dma-direction.h +#[derive(Copy, Clone, PartialEq, Eq, Debug)] +#[repr(u32)] +pub enum DataDirection { + /// The DMA mapping is for bidirectional data transfer. + /// + /// This is used when the buffer can be both read from and written to by the device. + /// The cache for the corresponding memory region is both flushed and invalidated. + Bidirectional = Self::const_cast(bindings::dma_data_direction_DMA_BIDIRECTIONAL), + + /// The DMA mapping is for data transfer from memory to the device (write). + /// + /// The CPU has prepared data in the buffer, and the device will read it. + /// The cache for the corresponding memory region is flushed before device access. + ToDevice = Self::const_cast(bindings::dma_data_direction_DMA_TO_DEVICE), + + /// The DMA mapping is for data transfer from the device to memory (read). + /// + /// The device will write data into the buffer for the CPU to read. + /// The cache for the corresponding memory region is invalidated before CPU access. + FromDevice = Self::const_cast(bindings::dma_data_direction_DMA_FROM_DEVICE), + + /// The DMA mapping is not for data transfer. + /// + /// This is primarily for debugging purposes. With this direction, the DMA mapping API + /// will not perform any cache coherency operations. + None = Self::const_cast(bindings::dma_data_direction_DMA_NONE), +} + +impl DataDirection { + /// Casts the bindgen-generated enum type to a `u32` at compile time. + /// + /// This function will cause a compile-time error if the underlying value of the + /// C enum is out of bounds for `u32`. + const fn const_cast(val: bindings::dma_data_direction) -> u32 { + // CAST: The C standard allows compilers to choose different integer types for enums. + // To safely check the value, we cast it to a wide signed integer type (`i128`) + // which can hold any standard C integer enum type without truncation. + let wide_val = val as i128; + + // Check if the value is outside the valid range for the target type `u32`. + // CAST: `u32::MAX` is cast to `i128` to match the type of `wide_val` for the comparison. + if wide_val < 0 || wide_val > u32::MAX as i128 { + // Trigger a compile-time error in a const context. + build_error!("C enum value is out of bounds for the target type `u32`."); + } + + // CAST: This cast is valid because the check above guarantees that `wide_val` + // is within the representable range of `u32`. + wide_val as u32 + } +} + +impl From for bindings::dma_data_direction { + /// Returns the raw representation of [`enum dma_data_direction`]. + fn from(direction: DataDirection) -> Self { + // CAST: `direction as u32` gets the underlying representation of our `#[repr(u32)]` enum. + // The subsequent cast to `Self` (the bindgen type) assumes the C enum is compatible + // with the enum variants of `DataDirection`, which is a valid assumption given our + // compile-time checks. + direction as u32 as Self + } +} + /// An abstraction of the `dma_alloc_coherent` API. /// /// This is an abstraction around the `dma_alloc_coherent` API which is used to allocate and map -- 2.51.0