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

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Message-Id: <DDT3CXES4BXF.2YWJLBR0XDAUP@nvidia.com>
Date: Mon, 27 Oct 2025 21:08:44 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Danilo Krummrich" <dakr@...nel.org>, "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>, "Nouveau"
 <nouveau-bounces@...ts.freedesktop.org>
Subject: Re: [PATCH 5/7] gpu: nova-core: add extra conversion functions and
 traits

On Mon Oct 27, 2025 at 12:40 AM JST, Danilo Krummrich wrote:
> 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.

That's correct.

>
> 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.

We'll definitely want this. Nova-core does not use require signed types,
which is why I omitted them for now - and also so save some labor as we
are still discussing the fitness of this design.