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From: Andreas Hindborg <a.hindborg@kernel.org>
To: Gary Guo <gary@garyguo.net>, Greg Kroah-Hartman
 <gregkh@linuxfoundation.org>, "Rafael J. Wysocki" <rafael@kernel.org>,
 Danilo Krummrich <dakr@kernel.org>, Miguel Ojeda <ojeda@kernel.org>, Boqun
 Feng <boqun@kernel.org>, Gary Guo <gary@garyguo.net>, =?utf-8?Q?Bj=C3=B6r?=
 =?utf-8?Q?n?= Roy Baron
 <bjorn3_gh@protonmail.com>, Benno Lossin <lossin@kernel.org>, Alice Ryhl
 <aliceryhl@google.com>, Trevor Gross <tmgross@umich.edu>, Daniel Almeida
 <daniel.almeida@collabora.com>, Bjorn Helgaas <bhelgaas@google.com>,
 Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= <kwilczynski@kernel.org>, Abdiel
 Janulgue
 <abdiel.janulgue@gmail.com>, Robin Murphy <robin.murphy@arm.com>,
 Alexandre Courbot <acourbot@nvidia.com>, David Airlie <airlied@gmail.com>,
 Simona Vetter <simona@ffwll.ch>
Cc: driver-core@lists.linux.dev, rust-for-linux@vger.kernel.org,
 linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
 nouveau@lists.freedesktop.org, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH v2 08/11] rust: io: add `read_val` and `write_val`
 function on I/O view
In-Reply-To: <20260421-io_projection-v2-8-4c251c692ef4@garyguo.net>
References: <20260421-io_projection-v2-0-4c251c692ef4@garyguo.net>
 <20260421-io_projection-v2-8-4c251c692ef4@garyguo.net>
Date: Tue, 28 Apr 2026 14:53:39 +0200
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Gary Guo <gary@garyguo.net> writes:

> When a view is narrowed to just a primitive, these functions provide a way
> to access them using the `IoCapable` trait. This is used to provide
> `io_read!` and `io_write!` macros, which are generalized version of current
> `dma_read!` and `dma_write!` macro (that works on `Coherent` only, but not
> subview of them, or other I/O backends).
>
> For DMA coherent objects, `IoCapable` is only implemented for atomically
> accessible primitives; this is because `read_volatile`/`write_volatile` can
> behave undesirably for aggregates; LLVM may turn them to multiple
> instructions to access parts and assemble, or could combine them to a
> single instruction.
>
> The ability to read/write aggregates (when atomicity is of no concern),
> could be implemented with copying primitives (e.g. memcpy_{from,to}io) in
> the future.
>
> Signed-off-by: Gary Guo <gary@garyguo.net>

Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>


Best regards,
Andreas Hindborg