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Message-ID: <aKLzrp0m00J6CCYz@google.com>
Date: Mon, 18 Aug 2025 09:34:38 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: akpm@...ux-foundation.org, ojeda@...nel.org, alex.gaynor@...il.com,
boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com,
lossin@...nel.org, a.hindborg@...nel.org, tmgross@...ch.edu,
abdiel.janulgue@...il.com, acourbot@...dia.com, jgg@...pe.ca,
lyude@...hat.com, robin.murphy@....com, daniel.almeida@...labora.com,
rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] rust: dma: implement DataDirection
On Fri, Aug 15, 2025 at 07:10:02PM +0200, Danilo Krummrich wrote:
> 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 <dakr@...nel.org>
> +/// 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)]
> +pub struct DataDirection(bindings::dma_data_direction);
Perhaps this should be a real Rust enum so that you can do an exhaustive
match?
> +impl 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.
> + pub const BIDIRECTIONAL: DataDirection =
> + DataDirection(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.
> + pub const TO_DEVICE: DataDirection = DataDirection(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.
> + pub const FROM_DEVICE: DataDirection =
> + DataDirection(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.
> + pub const NONE: DataDirection = DataDirection(bindings::dma_data_direction_DMA_NONE);
> +
> + /// Returns the raw representation of [`enum dma_data_direction`].
> + pub fn as_raw(self) -> bindings::dma_data_direction {
> + self.0
> + }
> +}
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