linux-kernel - Re: [PATCH] drm: nova-drm: fix 32-bit arm build

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Message-Id: <DBKG6CA32OO0.368N1Y6VMIUTL@kernel.org>
Date: Thu, 24 Jul 2025 19:05:26 +0200
From: "Danilo Krummrich" <dakr@...nel.org>
To: "Miguel Ojeda" <ojeda@...nel.org>
Cc: "David Airlie" <airlied@...il.com>, "Simona Vetter" <simona@...ll.ch>,
 "Alex Gaynor" <alex.gaynor@...il.com>, <nouveau@...ts.freedesktop.org>,
 <dri-devel@...ts.freedesktop.org>, "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>, "Alice Ryhl" <aliceryhl@...gle.com>,
 "Trevor Gross" <tmgross@...ch.edu>, <rust-for-linux@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <patches@...ts.linux.dev>
Subject: Re: [PATCH] drm: nova-drm: fix 32-bit arm build

On Thu Jul 24, 2025 at 6:54 PM CEST, Miguel Ojeda wrote:
> In 32-bit arm, the build fails with:
>
>     error[E0308]: mismatched types
>       --> drivers/gpu/drm/nova/file.rs:42:28
>        |
>     42 |         getparam.set_value(value);
>        |                  --------- ^^^^^ expected `u64`, found `u32`
>        |                  |
>        |                  arguments to this method are incorrect
>        |
>     note: method defined here
>       --> drivers/gpu/drm/nova/uapi.rs:29:12
>        |
>     29 |     pub fn set_value(&self, v: u64) {
>        |            ^^^^^^^^^        ------
>     help: you can convert a `u32` to a `u64`
>        |
>     42 |         getparam.set_value(value.into());
>        |                                 +++++++
>
> The reason is that `Getparam::set_value` takes a `u64` (from the UAPI),
> but `pci::Device::resource_len()` returns a `resource_size_t`, which is a
> `phys_addr_t`, which may be 32- or 64-bit.
>
> Thus add an `into()` call to support the 32-bit case, while allowing the
> Clippy lint that complains in the 64-bit case where the type is the same.
>
> Fixes: cdeaeb9dd762 ("drm: nova-drm: add initial driver skeleton")
> Signed-off-by: Miguel Ojeda <ojeda@...nel.org>

Thanks -- will take it through -fixes once rc-1 is out.

> ---
> As discussed, it may be best to have a newtype, or at least a function
> to perform this -- here it is the minimal fix nevertheless.

I think I will follow up with a function to perform the conversion in a single
place, but I really like the idea of a special clippy annotation to tell clippy
to not warn about unnecessary into() conversions for a specific type alias, such
as ResourceSize.

Do we agree that we want something like this? Do we even have a feature request
for this already?