linux-kernel - Re: [PATCH 5/7] gpu: nova-core: add extra conversion functions and traits

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Message-ID: <cb1026f8-5bf3-418d-bbd5-50c0b63de0db@kernel.org>
Date: Sun, 26 Oct 2025 16:40:23 +0100
From: Danilo Krummrich <dakr@...nel.org>
To: Alexandre Courbot <acourbot@...dia.com>
Cc: Alice Ryhl <aliceryhl@...gle.com>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Miguel Ojeda <ojeda@...nel.org>,
 Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>,
 Gary Guo <gary@...yguo.net>, Björn Roy Baron
 <bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>,
 Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>,
 John Hubbard <jhubbard@...dia.com>, Alistair Popple <apopple@...dia.com>,
 Joel Fernandes <joelagnelf@...dia.com>, Timur Tabi <ttabi@...dia.com>,
 Edwin Peer <epeer@...dia.com>, nouveau@...ts.freedesktop.org,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org
Subject: Re: [PATCH 5/7] gpu: nova-core: add extra conversion functions and
 traits

On 10/26/25 3:39 PM, Alexandre Courbot wrote:
> +#[cfg(CONFIG_32BIT)]
> +/// Infallibly converts a `usize` to `u32` on 32-bit platforms.
> +///
> +/// This conversion is always lossless on 32-bit platforms, where a `usize` is the same size as a
> +/// `u32`.
> +///
> +/// Prefer this over the `as` keyword to ensure no lossy conversions are performed.
> +///
> +/// This is for use from a `const` context. For non `const` use, prefer the [`FromAs`] and
> +/// [`IntoAs`] traits.
> +pub(crate) const fn usize_as_u32(value: usize) -> u32 {
> +    kernel::static_assert!(size_of::<u32>() >= size_of::<usize>());
> +
> +    value as u32
> +}

Given that nova-core depends on CONFIG_64BIT, I assume you added this predicting
that we'll move this to the kernel crate.

For core code (and maybe other drivers) I think we also want the same thing for
signed types, but I think it's also fine to add them when moving things into the
kernel crate.