From nobody Sat Oct 4 04:59:47 2025 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 276E132779F; Wed, 20 Aug 2025 16:54:49 +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=1755708890; cv=none; b=jDIGg5jcXgj2Rvh6XCYr/wkDTN43RP7Da+tDq9HwTdhYuDImcxexBBDU9wDv4jdm75DZXleG/T9pd0vTh0hB7v8TqRLTUYA5kor/ADclnIMySSLzz/F0FkEtW6sNYozoRmOdpLNUww1l/0FYX7hKQkwj0D83dBUwPyTBiJZM1BI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755708890; c=relaxed/simple; bh=ZuG4V3x4Aoyo3VVzpfFRO87y1Z8MNkIM9ec01WX1rUg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Gdvt0JrCigzhAKkyLO4QTkkO/UHrEsvi+dcOermQ3cK6iUxKUJcSVUT31wyFMBN10mqHw3Fu1az9prC+r4nKlDqaggXMZsog8i4hj1NYpoarz4Khim/3w8/iZEE7ZeLpOdmF/9v0eSSajs2vHtksBjXeAj4maD+wu94d2X7nH2w= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Am2GhER3; 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="Am2GhER3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 457ADC116B1; Wed, 20 Aug 2025 16:54:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1755708889; bh=ZuG4V3x4Aoyo3VVzpfFRO87y1Z8MNkIM9ec01WX1rUg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Am2GhER3GBoQMdaiqDqxSuhOeTsUUfhPgaoIk9+RXL/xfZOYx0BZQpECCAJP3UW9m wAnz2T1xjj2E6UWtN/P9sQ3Wzv688fIi/TKAZ2rNacuNEMPOqJ1haytw4w52WZKZZz LlNoqfvb63EWHkmF5HM92vRXVvJhhofsCGarPU0tj9qH/ad55gQjqLt+fMPfVChmlX R/DlzFG3qDc4x62VuF4c3MMl6ZjcBtNJcWqnejRfENQl+06OcwAIh+S4Io6g+zn4ny PM0bnyvGt8sHFeyGyIFHCP03XYtkF5fvOWnid6Rka6E4+M3d1xUOsmJ/R742aPxOGa lR0u2eNvS7JZA== 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 v2 1/5] rust: dma: implement DataDirection Date: Wed, 20 Aug 2025 18:52:55 +0200 Message-ID: <20250820165431.170195-2-dakr@kernel.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250820165431.170195-1-dakr@kernel.org> References: <20250820165431.170195-1-dakr@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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. Signed-off-by: Danilo Krummrich Reviewed-by: Alexandre Courbot Reviewed-by: Alice Ryhl --- 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_helpe= r.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..5daba00ecc78 100644 --- a/rust/kernel/dma.rs +++ b/rust/kernel/dma.rs @@ -244,6 +244,74 @@ pub mod attrs { pub const DMA_ATTR_PRIVILEGED: Attrs =3D Attrs(bindings::DMA_ATTR_PRIV= ILEGED); } =20 +/// 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 =3D Self::const_cast(bindings::dma_data_direction_DMA_BI= DIRECTIONAL), + + /// The DMA mapping is for data transfer from memory to the device (wr= ite). + /// + /// The CPU has prepared data in the buffer, and the device will read = it. + /// The cache for the corresponding memory region is flushed. + ToDevice =3D Self::const_cast(bindings::dma_data_direction_DMA_TO_DEVI= CE), + + /// The DMA mapping is for data transfer from the device to memory (re= ad). + /// + /// The device will write data into the buffer for the CPU to read. + /// The cache for the corresponding memory region is invalidated befor= e CPU access. + FromDevice =3D 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 =3D 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 va= lue 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 integ= er 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 truncat= ion. + let wide_val =3D val as i128; + + // Check if the value is outside the valid range for the target ty= pe `u32`. + // CAST: `u32::MAX` is cast to `i128` to match the type of `wide_v= al` 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 typ= e `u32`."); + } + + // CAST: This cast is valid because the check above guarantees tha= t `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 ass= umption 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 us= ed to allocate and map --=20 2.50.1