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Date: Thu, 17 Sep 2026 10:50:58 +0200
Message-Id: <DLHGOK4T4SCX.37QOVMLFTYFFQ@kernel.org>
Subject: Re: [PATCH v4 1/2] rust: num: add cv! macro to create values from
 constant expressions
Cc: "Alexandre Courbot" <acourbot@nvidia.com>, "Yury Norov"
 <yury.norov@gmail.com>, "Miguel Ojeda" <ojeda@kernel.org>, "Boqun Feng"
 <boqun@kernel.org>, "Gary Guo" <gary@garyguo.net>,
 =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>, "Benno Lossin"
 <lossin@kernel.org>, "Andreas Hindborg" <a.hindborg@kernel.org>, "Alice
 Ryhl" <aliceryhl@google.com>, "Trevor Gross" <tmgross@umich.edu>, "Daniel
 Almeida" <daniel.almeida@collabora.com>, "Tamir Duberstein"
 <tamird@kernel.org>, =?utf-8?q?Onur_=C3=96zkan?= <work@onurozkan.dev>,
 "David Airlie" <airlied@gmail.com>, "Simona Vetter" <simona@ffwll.ch>,
 "John Hubbard" <jhubbard@nvidia.com>, "Alistair Popple"
 <apopple@nvidia.com>, "Timur Tabi" <ttabi@nvidia.com>,
 <rust-for-linux@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
 <nova-gpu@lists.linux.dev>, <dri-devel@lists.freedesktop.org>
To: "Eliot Courtney" <ecourtney@nvidia.com>
From: "Danilo Krummrich" <dakr@kernel.org>
References: <20260917-cv-v4-0-547ef5727451@nvidia.com>
 <20260917-cv-v4-1-547ef5727451@nvidia.com>
In-Reply-To: <20260917-cv-v4-1-547ef5727451@nvidia.com>

On Thu Sep 17, 2026 at 10:34 AM CEST, Eliot Courtney wrote:
> Currently, using NonZero/Bounded constants is quite verbose. It's
> unfortunate because it disincentivizes using it in interface boundaries.
> Introduce a macro to make it nicer to use. The macro `cv!` (for constant
> value) takes a const integer expression and widens it to i128 (at build
> time only) before passing it as a const generic value to a new trait
> `FromConst`. The value is then converted and appears in the
> associated constant `FromConst::VALUE`. The trait is implemented by
> NonZero, Bounded, and Alignment and lets values of each be constructed
> from constants without a verbose turbofish syntax.
> For example, `const { NonZero::new(1).unwrap() }` can be written as
> `cv!(1)`.
>
> Add the `cv!` macro to the prelude so it doesn't need to be imported
> explicitly to use it.
>
> Suggested-by: Gary Guo <gary@garyguo.net>
> Reviewed-by: Gary Guo <gary@garyguo.net>
> Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>

Acked-by: Danilo Krummrich <dakr@kernel.org>

> +/// use core::num::NonZero;
> +/// use kernel::num::Bounded;
> +/// use kernel::ptr::Alignment;

NIT: Let's use the kernel's import style.