linux-kernel - Re: [PATCH 6/9] rust: dma: add dma_read! and dma

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Message-ID: <CAH5fLggBd6s5MooGPfUaoarNF651BjTyBt+KcuJc0zdx5xg7cg@mail.gmail.com>
Date: Fri, 30 Jan 2026 11:26:44 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Eliot Courtney <ecourtney@...dia.com>
Cc: Danilo Krummrich <dakr@...nel.org>, Alexandre Courbot <acourbot@...dia.com>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Abdiel Janulgue <abdiel.janulgue@...il.com>, Daniel Almeida <daniel.almeida@...labora.com>, 
	Robin Murphy <robin.murphy@....com>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Miguel Ojeda <ojeda@...nel.org>, Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <lossin@...nel.org>, Trevor Gross <tmgross@...ch.edu>, nouveau@...ts.freedesktop.org, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	driver-core@...ts.linux.dev, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH 6/9] rust: dma: add dma_read! and dma_write! macros

On Fri, Jan 30, 2026 at 9:35 AM Eliot Courtney <ecourtney@...dia.com> wrote:
>
> Add dma_read! and dma_write! macros using the new infallible methods
> on CoherentArray.
>
> Signed-off-by: Eliot Courtney <ecourtney@...dia.com>
> ---
>  rust/kernel/dma.rs | 103 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 103 insertions(+)
>
> diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs
> index e4bca7a18ac1..f3920f74583a 100644
> --- a/rust/kernel/dma.rs
> +++ b/rust/kernel/dma.rs
> @@ -811,6 +811,24 @@ pub unsafe fn as_slice_mut<const OFFSET: usize, const COUNT: usize>(&mut self) -
>              )
>          };
>      }
> +
> +    /// Returns a pointer to an element from the region with bounds checking. `OFFSET` is in
> +    /// units of `T`, not the number of bytes.
> +    ///
> +    /// Public but hidden since it should only be used from [`dma_read`] and [`dma_write`] macros.
> +    #[doc(hidden)]
> +    pub fn ptr_at<const OFFSET: usize>(&self) -> *mut T {
> +        build_assert!(
> +            OFFSET < N,
> +            "Index out of bounds when accessing CoherentArray"
> +        );

This build assert does not depend on runtime values, so it can be
written as a const block:
const { assert!(OFFSET < N, "Index out of bounds when accessing
CoherentArray"); }

Alice