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

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Message-Id: <DFV4RTLGQU1C.1FNHL8AC2DW2L@kernel.org>
Date: Thu, 22 Jan 2026 13:52:29 +0100
From: "Danilo Krummrich" <dakr@...nel.org>
To: "Zhi Wang" <zhiw@...dia.com>
Cc: <rust-for-linux@...r.kernel.org>, <linux-pci@...r.kernel.org>,
 <linux-kernel@...r.kernel.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>,
 <acourbot@...dia.com>, <joelagnelf@...dia.com>, <jhubbard@...dia.com>,
 <zhiwang@...nel.org>, <daniel.almeida@...labora.com>,
 <ukleinek@...nel.org>, <m.wilczynski@...sung.com>
Subject: Re: [PATCH v12 2/5] rust: io: separate generic I/O helpers from
 MMIO implementation

(Cc: Uwe, Michal)

On Wed Jan 21, 2026 at 9:22 PM CET, 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>
> ---
>  drivers/gpu/drm/tyr/regs.rs            |   1 +
>  drivers/gpu/nova-core/gsp/sequencer.rs |   5 +-
>  drivers/gpu/nova-core/regs/macros.rs   |  90 +++---
>  drivers/gpu/nova-core/vbios.rs         |   1 +
>  drivers/pwm/pwm_th1520.rs              |   5 +-
>  rust/kernel/devres.rs                  |  19 +-
>  rust/kernel/io.rs                      | 398 ++++++++++++++++++++-----
>  rust/kernel/io/mem.rs                  |  16 +-
>  rust/kernel/io/poll.rs                 |  16 +-
>  rust/kernel/pci/io.rs                  |  12 +-
>  samples/rust/rust_driver_pci.rs        |   1 +
>  11 files changed, 433 insertions(+), 131 deletions(-)

<snip>

> diff --git a/drivers/pwm/pwm_th1520.rs b/drivers/pwm/pwm_th1520.rs
> index e3b7e77356fc..616ca398b2c5 100644
> --- a/drivers/pwm/pwm_th1520.rs
> +++ b/drivers/pwm/pwm_th1520.rs
> @@ -26,7 +26,10 @@
>      clk::Clk,
>      device::{Bound, Core, Device},
>      devres,
> -    io::mem::IoMem,
> +    io::{
> +        mem::IoMem,
> +        Io, //
> +    },
>      of, platform,
>      prelude::*,
>      pwm, time,