Re: [PATCH 1/4] rust: dma: implement DataDirection

[Alice Ryhl <aliceryhl@google.com>]

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@kernel.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
> +    }
> +}