Re: [PATCH v2 3/8] rust: dma: add zeroed constructor to `Coherent`

[Andreas Hindborg <a.hindborg@kernel.org>]

"Danilo Krummrich" <dakr@kernel.org> writes:

> From: Gary Guo <gary@garyguo.net>
>
> These constructors create a coherent container of a single object
> instead of slice. They are named `zeroed` and `zeroed_with_attrs` to
> emphasis that they are created initialized zeroed. It is intended that
> there'll be new constructors that take `PinInit` instead of zeroing.
>
> Signed-off-by: Gary Guo <gary@garyguo.net>
> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>
> ---
>  rust/kernel/dma.rs       | 81 ++++++++++++++++++++++++++++++++++++----
>  samples/rust/rust_dma.rs |  8 ++--
>  2 files changed, 77 insertions(+), 12 deletions(-)
>
> diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs
> index ff3e147f1a23..db645b01bdd0 100644
> --- a/rust/kernel/dma.rs
> +++ b/rust/kernel/dma.rs
> @@ -47,7 +47,7 @@ pub trait Device: AsRef<device::Device<Core>> {
>      /// # Safety
>      ///
>      /// This method must not be called concurrently with any DMA allocation or mapping primitives,
> -    /// such as [`CoherentAllocation::alloc_attrs`].
> +    /// such as [`Coherent::zeroed`].
>      unsafe fn dma_set_mask(&self, mask: DmaMask) -> Result {
>          // SAFETY:
>          // - By the type invariant of `device::Device`, `self.as_ref().as_raw()` is valid.
> @@ -64,7 +64,7 @@ unsafe fn dma_set_mask(&self, mask: DmaMask) -> Result {
>      /// # Safety
>      ///
>      /// This method must not be called concurrently with any DMA allocation or mapping primitives,
> -    /// such as [`CoherentAllocation::alloc_attrs`].
> +    /// such as [`Coherent::zeroed`].
>      unsafe fn dma_set_coherent_mask(&self, mask: DmaMask) -> Result {
>          // SAFETY:
>          // - By the type invariant of `device::Device`, `self.as_ref().as_raw()` is valid.
> @@ -83,7 +83,7 @@ unsafe fn dma_set_coherent_mask(&self, mask: DmaMask) -> Result {
>      /// # Safety
>      ///
>      /// This method must not be called concurrently with any DMA allocation or mapping primitives,
> -    /// such as [`CoherentAllocation::alloc_attrs`].
> +    /// such as [`Coherent::zeroed`].
>      unsafe fn dma_set_mask_and_coherent(&self, mask: DmaMask) -> Result {
>          // SAFETY:
>          // - By the type invariant of `device::Device`, `self.as_ref().as_raw()` is valid.
> @@ -102,7 +102,7 @@ unsafe fn dma_set_mask_and_coherent(&self, mask: DmaMask) -> Result {
>      /// # Safety
>      ///
>      /// This method must not be called concurrently with any DMA allocation or mapping primitives,
> -    /// such as [`CoherentAllocation::alloc_attrs`].
> +    /// such as [`Coherent::zeroed`].
>      unsafe fn dma_set_max_seg_size(&self, size: u32) {
>          // SAFETY:
>          // - By the type invariant of `device::Device`, `self.as_ref().as_raw()` is valid.
> @@ -202,12 +202,12 @@ pub const fn value(&self) -> u64 {
>  ///
>  /// ```
>  /// # use kernel::device::{Bound, Device};
> -/// use kernel::dma::{attrs::*, CoherentAllocation};
> +/// use kernel::dma::{attrs::*, Coherent};
>  ///
>  /// # fn test(dev: &Device<Bound>) -> Result {
>  /// let attribs = DMA_ATTR_FORCE_CONTIGUOUS | DMA_ATTR_NO_WARN;
> -/// let c: CoherentAllocation<u64> =
> -///     CoherentAllocation::alloc_attrs(dev, 4, GFP_KERNEL, attribs)?;
> +/// let c: Coherent<[u64]> =
> +///     Coherent::zeroed_slice_with_attrs(dev, 4, GFP_KERNEL, attribs)?;
>  /// # Ok::<(), Error>(()) }
>  /// ```
>  #[derive(Clone, Copy, PartialEq)]
> @@ -492,7 +492,6 @@ pub unsafe fn field_write<F: AsBytes>(&self, field: *mut F, val: F) {
>
>  impl<T: AsBytes + FromBytes> Coherent<T> {
>      /// Allocates a region of `T` of coherent memory.
> -    #[expect(unused)]
>      fn alloc_with_attrs(
>          dev: &device::Device<Bound>,
>          gfp_flags: kernel::alloc::Flags,
> @@ -529,6 +528,35 @@ fn alloc_with_attrs(
>          })
>      }
>
> +    /// Allocates a region of type `T` of coherent memory.

For consistency "Allocates a ZEROED region...".

> +    ///
> +    /// # Examples
> +    ///
> +    /// ```
> +    /// # use kernel::device::{Bound, Device};
> +    /// use kernel::dma::{attrs::*, Coherent};
> +    ///
> +    /// # fn test(dev: &Device<Bound>) -> Result {
> +    /// let c: Coherent<[u64; 4]> =
> +    ///     Coherent::zeroed_with_attrs(dev, GFP_KERNEL, DMA_ATTR_NO_WARN)?;
> +    /// # Ok::<(), Error>(()) }
> +    /// ```
> +    #[inline]
> +    pub fn zeroed_with_attrs(
> +        dev: &device::Device<Bound>,
> +        gfp_flags: kernel::alloc::Flags,
> +        dma_attrs: Attrs,
> +    ) -> Result<Self> {
> +        Self::alloc_with_attrs(dev, gfp_flags | __GFP_ZERO, dma_attrs)
> +    }
> +
> +    /// Performs the same functionality as [`Coherent::zeroed_with_attrs`], except the
> +    /// `dma_attrs` is 0 by default.
> +    #[inline]
> +    pub fn zeroed(dev: &device::Device<Bound>, gfp_flags: kernel::alloc::Flags) -> Result<Self> {
> +        Self::zeroed_with_attrs(dev, gfp_flags, Attrs(0))
> +    }
> +
>      /// Allocates a region of `[T; len]` of coherent memory.
>      fn alloc_slice_with_attrs(
>          dev: &device::Device<Bound>,
> @@ -572,6 +600,43 @@ fn alloc_slice_with_attrs(
>              dma_attrs,
>          })
>      }
> +
> +    /// Allocates a zeroed region of type `T` of coherent memory.

Should it be "of type `[T]`"?


Best regards,
Andreas Hindborg