[PATCH] rust: allow `clippy::as_underscore` in the generated bindings

[PATCH] rust: allow `clippy::as_underscore` in the generated bindings

[John Hubbard]

A CLIPPY=1 build emitted about 15000 `as _` conversion warnings, all of
them in bindgen's generated output and none in hand-written code.

bindgen 0.73 returns each bitfield read through a trailing `as _`, and
0.72 returns it through a transmute, which the lint ignores. The
bindings and uapi crates allow `clippy::all` over the generated code.
That group does not cover `clippy::as_underscore`, a restriction lint.

The minimum supported bindgen is 0.71.1, and 0.72 does not emit the
cast, so upstream CI may not see these warnings yet.

Allow `clippy::as_underscore` by name in the bindings and uapi crates.

Assisted-by: LLM
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 rust/bindings/lib.rs | 1 +
 rust/uapi/lib.rs     | 1 +
 2 files changed, 2 insertions(+)

diff --git a/rust/bindings/lib.rs b/rust/bindings/lib.rs
index 812f8e5a08d5..ad24c920b919 100644
--- a/rust/bindings/lib.rs
+++ b/rust/bindings/lib.rs
@@ -22,6 +22,7 @@
 #![feature(cfi_encoding)]
 
 #[allow(dead_code)]
+#[allow(clippy::as_underscore)]
 #[allow(clippy::cast_lossless)]
 #[allow(clippy::ptr_as_ptr)]
 #[allow(clippy::ref_as_ptr)]
diff --git a/rust/uapi/lib.rs b/rust/uapi/lib.rs
index 797ead5b5626..2df0340e63d1 100644
--- a/rust/uapi/lib.rs
+++ b/rust/uapi/lib.rs
@@ -10,6 +10,7 @@
 #![no_std]
 #![allow(
     clippy::all,
+    clippy::as_underscore,
     clippy::cast_lossless,
     clippy::ptr_as_ptr,
     clippy::ref_as_ptr,

base-commit: 1676a4478e434d43f8cab79587becd16d3e86552
-- 
2.55.0

Re: [PATCH] rust: allow `clippy::as_underscore` in the generated bindings

[Miguel Ojeda]

On Sun, Sep 6, 2026 at 11:58 PM John Hubbard <jhubbard@nvidia.com> wrote:
>
> A CLIPPY=1 build emitted about 15000 `as _` conversion warnings, all of
> them in bindgen's generated output and none in hand-written code.
>
> bindgen 0.73 returns each bitfield read through a trailing `as _`, and
> 0.72 returns it through a transmute, which the lint ignores. The
> bindings and uapi crates allow `clippy::all` over the generated code.
> That group does not cover `clippy::as_underscore`, a restriction lint.
>
> The minimum supported bindgen is 0.71.1, and 0.72 does not emit the
> cast, so upstream CI may not see these warnings yet.
>
> Allow `clippy::as_underscore` by name in the bindings and uapi crates.
>
> Assisted-by: LLM
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>

Thanks! Looks good to me.

We have been getting 0.73.0 and 0.73.1 fixed for a correctness issue I
noticed and I didn't see these yet -- I definitely recommend avoiding
those versions for kernel builds.

Cheers,
Miguel

Re: [PATCH] rust: allow `clippy::as_underscore` in the generated bindings

[Miguel Ojeda]

On Mon, Sep 7, 2026 at 12:48 AM Miguel Ojeda
<miguel.ojeda.sandonis@gmail.com> wrote:
>
> Thanks! Looks good to me.
>
> We have been getting 0.73.0 and 0.73.1 fixed for a correctness issue I
> noticed and I didn't see these yet -- I definitely recommend avoiding
> those versions for kernel builds.

And by "we" I mean mostly Emilio (Cc'd :).

By the way, what do you mean by:

  The minimum supported bindgen is 0.71.1, and 0.72 does not emit the
  cast, so upstream CI may not see these warnings yet.

? i.e. what is the "upstream CI"? I am not sure which one is the base
commit either, so perhaps this is about some CI in DRM or similar? In
any case, I think I will remove that bit from the message since I am
not sure what it is meant to add, but if I am missing something,
please let me know!

Cheers,
Miguel

Re: [PATCH] rust: allow `clippy::as_underscore` in the generated bindings

[John Hubbard]

On 9/6/26 3:56 PM, Miguel Ojeda wrote:
> On Mon, Sep 7, 2026 at 12:48 AM Miguel Ojeda
> <miguel.ojeda.sandonis@gmail.com> wrote:
>>
>> Thanks! Looks good to me.
>>
>> We have been getting 0.73.0 and 0.73.1 fixed for a correctness issue I
>> noticed and I didn't see these yet -- I definitely recommend avoiding
>> those versions for kernel builds.

Arch Linux, always grabbing something new, for better or worse, here. :)

> 
> And by "we" I mean mostly Emilio (Cc'd :).
> 
> By the way, what do you mean by:
> 
>    The minimum supported bindgen is 0.71.1, and 0.72 does not emit the
>    cast, so upstream CI may not see these warnings yet.
> 
> ? i.e. what is the "upstream CI"? I am not sure which one is the base
> commit either, so perhaps this is about some CI in DRM or similar? In

That's just me guessing about how this was overlooked. Yes, go ahead
and remove it.

> any case, I think I will remove that bit from the message since I am
> not sure what it is meant to add, but if I am missing something,
> please let me know!
> 
> Cheers,
> Miguel

thanks,
-- 
John Hubbard

Re: [PATCH] rust: allow `clippy::as_underscore` in the generated bindings

[Miguel Ojeda]

On Sun, Sep 6, 2026 at 11:58 PM John Hubbard <jhubbard@nvidia.com> wrote:
>
> A CLIPPY=1 build emitted about 15000 `as _` conversion warnings, all of
> them in bindgen's generated output and none in hand-written code.
>
> bindgen 0.73 returns each bitfield read through a trailing `as _`, and
> 0.72 returns it through a transmute, which the lint ignores. The
> bindings and uapi crates allow `clippy::all` over the generated code.
> That group does not cover `clippy::as_underscore`, a restriction lint.
>
> The minimum supported bindgen is 0.71.1, and 0.72 does not emit the
> cast, so upstream CI may not see these warnings yet.
>
> Allow `clippy::as_underscore` by name in the bindings and uapi crates.
>
> Assisted-by: LLM
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>

Applied to `rust-fixes` so that we get it into linux-next since this
sort of thing can be quite annoying -- thanks!

    [ The lint messages look like:

        error: using `as _` conversion
             --> rust/bindings/bindings_generated.rs:18947:9
              |
        18947 |         self._bitfield_1.get_const::<0usize, 16u8>() as u32 as _
              |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
              |                                                                |
              |
        help: consider giving the type explicitly: `u32`
              |
              = help: for further information visit
https://rust-lang.github.io/rust-clippy/rust-1.98.0/index.html#as_underscore
              = note: `-D clippy::as-underscore` implied by `-D warnings`
              = help: to override `-D warnings` add
`#[allow(clippy::as_underscore)]`

        - Miguel ]

    [ Removed CI sentence. - Miguel ]

    Cc: stable@vger.kernel.org # Needed in 6.12.y and later (Rust is
pinned in older LTSs).

Technically it is not needed in 6.12.y since the lint is not enabled,
but it doesn't hurt, may help downstream trees and may simplify future
backports.

Cheers,
Miguel