linux-kernel - Re: [PATCH v12 2/3] rust: add dma coherent allocator abstraction.

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Message-ID: <87seo3z9qr.fsf@kernel.org>
Date: Mon, 24 Feb 2025 15:40:44 +0100
From: Andreas Hindborg <a.hindborg@...nel.org>
To: "Abdiel Janulgue" <abdiel.janulgue@...il.com>
Cc: <aliceryhl@...gle.com>,  <dakr@...nel.org>,  <robin.murphy@....com>,
  <daniel.almeida@...labora.com>,  <rust-for-linux@...r.kernel.org>,
  "Miguel Ojeda" <ojeda@...nel.org>,  "Alex Gaynor"
 <alex.gaynor@...il.com>,  "Boqun Feng" <boqun.feng@...il.com>,  "Gary Guo"
 <gary@...yguo.net>,  Björn Roy Baron
 <bjorn3_gh@...tonmail.com>,  "Benno
 Lossin" <benno.lossin@...ton.me>,  "Trevor Gross" <tmgross@...ch.edu>,
  "Valentin Obst" <kernel@...entinobst.de>,
  <linux-kernel@...r.kernel.org>,  "Christoph Hellwig" <hch@....de>,
  "Marek Szyprowski" <m.szyprowski@...sung.com>,  <airlied@...hat.com>,
  <iommu@...ts.linux.dev>
Subject: Re: [PATCH v12 2/3] rust: add dma coherent allocator abstraction.

"Abdiel Janulgue" <abdiel.janulgue@...il.com> writes:

[...]

> +/// Inform the kernel about the device's DMA addressing capabilities. This will set the mask for
> +/// both streaming and coherent APIs together.
> +pub fn dma_set_mask_and_coherent(dev: &Device, mask: u64) -> i32 {
> +    // SAFETY: device pointer is guaranteed as valid by invariant on `Device`.
> +    unsafe { bindings::dma_set_mask_and_coherent(dev.as_raw(), mask) }
> +}
> +
> +/// Same as `dma_set_mask_and_coherent`, but set the mask only for streaming mappings.
> +pub fn dma_set_mask(dev: &Device, mask: u64) -> i32 {
> +    // SAFETY: device pointer is guaranteed as valid by invariant on `Device`.
> +    unsafe { bindings::dma_set_mask(dev.as_raw(), mask) }
> +}

Sorry if it was asked before, I am late to the party. But would it make
sense to put these to functions on `Device` and make them take `&self`.

> +
> +/// Possible attributes associated with a DMA mapping.
> +///
> +/// They can be combined with the operators `|`, `&`, and `!`.
> +///
> +/// Values can be used from the [`attrs`] module.
> +#[derive(Clone, Copy, PartialEq)]
> +#[repr(transparent)]
> +pub struct Attrs(u32);
> +
> +impl Attrs {
> +    /// Get the raw representation of this attribute.
> +    pub(crate) fn as_raw(self) -> crate::ffi::c_ulong {
> +        self.0 as _
> +    }
> +
> +    /// Check whether `flags` is contained in `self`.
> +    pub fn contains(self, flags: Attrs) -> bool {
> +        (self & flags) == flags
> +    }
> +}
> +
> +impl core::ops::BitOr for Attrs {
> +    type Output = Self;
> +    fn bitor(self, rhs: Self) -> Self::Output {
> +        Self(self.0 | rhs.0)
> +    }
> +}
> +
> +impl core::ops::BitAnd for Attrs {
> +    type Output = Self;
> +    fn bitand(self, rhs: Self) -> Self::Output {
> +        Self(self.0 & rhs.0)
> +    }
> +}
> +
> +impl core::ops::Not for Attrs {
> +    type Output = Self;
> +    fn not(self) -> Self::Output {
> +        Self(!self.0)
> +    }
> +}
> +
> +/// DMA mapping attrributes.

Typo in attributes.

Best regards,
Andreas Hindborg