linux-kernel - Re: [PATCH v12 2/5] rust: io: separate generic I/O helpers from MMIO implementation

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Message-Id: <DFUU1K8VR3AV.1T258YBFZ62KS@nvidia.com>
Date: Thu, 22 Jan 2026 13:28:00 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Zhi Wang" <zhiw@...dia.com>
Cc: <rust-for-linux@...r.kernel.org>, <linux-pci@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <dakr@...nel.org>, <aliceryhl@...gle.com>,
 <bhelgaas@...gle.com>, <kwilczynski@...nel.org>, <ojeda@...nel.org>,
 <alex.gaynor@...il.com>, <boqun.feng@...il.com>, <gary@...yguo.net>,
 <bjorn3_gh@...tonmail.com>, <lossin@...nel.org>, <a.hindborg@...nel.org>,
 <tmgross@...ch.edu>, <markus.probst@...teo.de>, <helgaas@...nel.org>,
 <cjia@...dia.com>, <smitra@...dia.com>, <ankita@...dia.com>,
 <aniketa@...dia.com>, <kwankhede@...dia.com>, <targupta@...dia.com>,
 <joelagnelf@...dia.com>, <jhubbard@...dia.com>, <zhiwang@...nel.org>,
 <daniel.almeida@...labora.com>
Subject: Re: [PATCH v12 2/5] rust: io: separate generic I/O helpers from
 MMIO implementation

On Thu Jan 22, 2026 at 5:22 AM JST, Zhi Wang wrote:
> The previous Io<SIZE> type combined both the generic I/O access helpers
> and MMIO implementation details in a single struct. This coupling prevented
> reusing the I/O helpers for other backends, such as PCI configuration
> space.
>
> Establish a clean separation between the I/O interface and concrete
> backends by separating generic I/O helpers from MMIO implementation.
>
> Introduce a new trait hierarchy to handle different access capabilities:
>
> - IoCapable<T>: A marker trait indicating that a backend supports I/O
>   operations of a certain type (u8, u16, u32, or u64).
>
> - Io trait: Defines fallible (try_read8, try_write8, etc.) and infallibile
>   (read8, write8, etc.) I/O methods with runtime bounds checking and
>   compile-time bounds checking.
>
> - IoKnownSize trait: The marker trait for types support infallible I/O
>   methods.
>
> Move the MMIO-specific logic into a dedicated Mmio<SIZE> type that
> implements the Io traits. Rename IoRaw to MmioRaw and update consumers to
> use the new types.
>
> Cc: Alexandre Courbot <acourbot@...dia.com>
> Cc: Alice Ryhl <aliceryhl@...gle.com>
> Cc: Bjorn Helgaas <helgaas@...nel.org>
> Cc: Gary Guo <gary@...yguo.net>
> Cc: Danilo Krummrich <dakr@...nel.org>
> Cc: John Hubbard <jhubbard@...dia.com>
> Signed-off-by: Zhi Wang <zhiw@...dia.com>

I still hope we can make this evolve into something with less macros and
more accurate error handling (maybe following my earlier proposal if its
ideas are still relevant), but this is a great first step - thanks for
doing it!

[1] https://lore.kernel.org/all/DEMV14GBQWMC.28TXT8E5YO5NW@nvidia.com/

Reviewed-by: Alexandre Courbot <acourbot@...dia.com>