linux-kernel - Re: [PATCH v13 2/7] rust: add dma coherent allocator abstraction.

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Message-ID: <Z8rVsH_Hl34GUjOo@google.com>
Date: Fri, 7 Mar 2025 11:17:04 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Abdiel Janulgue <abdiel.janulgue@...il.com>
Cc: rust-for-linux@...r.kernel.org, daniel.almeida@...labora.com, 
	dakr@...nel.org, robin.murphy@....com, 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>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, 
	Valentin Obst <kernel@...entinobst.de>, open list <linux-kernel@...r.kernel.org>, 
	Christoph Hellwig <hch@....de>, Marek Szyprowski <m.szyprowski@...sung.com>, airlied@...hat.com, 
	"open list:DMA MAPPING HELPERS" <iommu@...ts.linux.dev>
Subject: Re: [PATCH v13 2/7] rust: add dma coherent allocator abstraction.

On Fri, Mar 07, 2025 at 01:06:19PM +0200, Abdiel Janulgue wrote:
> Add a simple dma coherent allocator rust abstraction. Based on
> Andreas Hindborg's dma abstractions from the rnvme driver, which
> was also based on earlier work by Wedson Almeida Filho.
> 
> A CoherentAllocation is wrapped in Devres which basically guarantees
> that a driver can't make a CoherentAllocation out-live driver unbind.
> This is needed, since DMA allocations potentially also result in
> programming of the IOMMU. IOMMU mappings are device resources and
> hence the device / driver lifecycle needs to be enforced.
> 
> Signed-off-by: Abdiel Janulgue <abdiel.janulgue@...il.com>

You might want to add #[inline] annotations to the various methods, but
otherwise LGTM.

Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>

> +/// Helper function to set the bit mask for DMA addressing.
> +pub const fn dma_bit_mask(n: usize) -> u64 {
> +    if n > 64 {
> +        return 0;
> +    }
> +    if n == 64 {
> +        !0
> +    } else {
> +        (1 << (n)) - 1
> +    }
> +}

You don't use this method?

Alice