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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 05/11] rust: io: restrict untyped IO access and
 `register!` to `Region`
In-Reply-To: <20260421-io_projection-v2-5-4c251c692ef4@garyguo.net>
References: <20260421-io_projection-v2-0-4c251c692ef4@garyguo.net>
 <20260421-io_projection-v2-5-4c251c692ef4@garyguo.net>
Date: Tue, 28 Apr 2026 11:02:34 +0200
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Gary Guo <gary@garyguo.net> writes:

> Currently the `Io` trait exposes a bunch of untyped IO accesses, but if the
> `Io` region itself is typed, then it might be weird to have
>
>     let io: Mmio<u32> = /* ... */;
>     io.read8(1);
>
> while not unsound, it is surely strange. Thus, restrict the untyped methods
> and also the register macro to `Region` type only.
>
> The way it is implemented is by adding a generic type to `IoLoc`. This also
> paves the way to add typed register blocks in the future; for example, we
> could use this mechanism to block driver A's `register!()` generated macro
> from being used on driver B's MMIO. The same mechanism could be used for
> relative IO registers. These are future opoortunities, and for this patch I
> just restricted everything to require `IoLoc<Region<SIZE>, _>`.

Does this not prevent `usize` from being used to index anything but
`Mmio<Region<_>>`?

It is my understanding that the following would work before this patch:

   fn do_read(io: &Mmio<u32>) -> Result {
       let v: u32 = io.try_read(8usize)?;
       Ok(())
   }

But I think this will no longer work with this patch. Is that the intention?


Best regards,
Andreas Hindborg