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Date: Sun, 26 Oct 2025 16:40:23 +0100
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Subject: Re: [PATCH 5/7] gpu: nova-core: add extra conversion functions and
 traits
To: Alexandre Courbot <acourbot@nvidia.com>
Cc: Alice Ryhl <aliceryhl@google.com>, David Airlie <airlied@gmail.com>,
 Simona Vetter <simona@ffwll.ch>, Miguel Ojeda <ojeda@kernel.org>,
 Alex Gaynor <alex.gaynor@gmail.com>, Boqun Feng <boqun.feng@gmail.com>,
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 <bjorn3_gh@protonmail.com>, Benno Lossin <lossin@kernel.org>,
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 John Hubbard <jhubbard@nvidia.com>, Alistair Popple <apopple@nvidia.com>,
 Joel Fernandes <joelagnelf@nvidia.com>, Timur Tabi <ttabi@nvidia.com>,
 Edwin Peer <epeer@nvidia.com>, nouveau@lists.freedesktop.org,
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 rust-for-linux@vger.kernel.org
References: <20251026-nova-as-v1-0-60c78726462d@nvidia.com>
 <20251026-nova-as-v1-5-60c78726462d@nvidia.com>
From: Danilo Krummrich <dakr@kernel.org>
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In-Reply-To: <20251026-nova-as-v1-5-60c78726462d@nvidia.com>
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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.