linux-kernel - Re: linux-next: build failure after merge of the rust tree

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Message-ID: <CAJ-ks9mTZZj2B=r3Xx8T8gvqPtGLL2bpFOfa9Qh49bi5xSahbQ@mail.gmail.com>
Date: Mon, 17 Nov 2025 10:37:07 -0500
From: Tamir Duberstein <tamird@...il.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Stephen Rothwell <sfr@...b.auug.org.au>, Miguel Ojeda <ojeda@...nel.org>, 
	Danilo Krummrich <dakr@...nel.org>, Alistair Popple <apopple@...dia.com>, John Hubbard <jhubbard@...dia.com>, 
	Alexandre Courbot <acourbot@...dia.com>, 
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, 
	Linux Next Mailing List <linux-next@...r.kernel.org>
Subject: Re: linux-next: build failure after merge of the rust tree

On Mon, Nov 17, 2025 at 9:51 AM Alice Ryhl <aliceryhl@...gle.com> wrote:
>
> On Mon, Nov 17, 2025 at 07:04:17PM +1100, Stephen Rothwell wrote:
> > Hi all,
> >
> > After merging the rust tree, today's linux-next build (x86_64
> > allmodconfig) failed like this:
> >
> > error[E0277]: `Chipset` doesn't implement `core::fmt::Display`
> >    --> drivers/gpu/nova-core/gpu.rs:233:13
> >     |
> > 233 |             self.chipset,
> >     |             ^^^^^^^^^^^^ `Chipset` cannot be formatted with the default formatter
> >     |
> >     = help: the trait `core::fmt::Display` is not implemented for `Chipset`
> >     = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
> >     = note: this error originates in the macro `$crate::format_args` which comes from the expansion of the macro `write` (in Nightly builds, run with -Z macro-backtrace for more info)
> >
> > error[E0277]: `Revision` doesn't implement `core::fmt::Display`
> >    --> drivers/gpu/nova-core/gpu.rs:235:13
> >     |
> > 235 |             self.revision
> >     |             ^^^^^^^^^^^^^ `Revision` cannot be formatted with the default formatter
> >     |
> >     = help: the trait `core::fmt::Display` is not implemented for `Revision`
> >     = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
> >     = note: this error originates in the macro `$crate::format_args` which comes from the expansion of the macro `write` (in Nightly builds, run with -Z macro-backtrace for more info)
> >
> > error[E0277]: the trait bound `MsgFunction: kernel::fmt::Display` is not satisfied
> >    --> drivers/gpu/nova-core/gsp/cmdq.rs:532:9
> >     |
> > 532 | /         dev_dbg!(
> > 533 | |             &self.dev,
> > 534 | |             "GSP RPC: send: seq# {}, function={}, length=0x{:x}\n",
> >     | |                                               -- required by a bound introduced by this call
> > 535 | |             self.seq,
> > 536 | |             M::FUNCTION,
> > 537 | |             dst.header.length(),
> > 538 | |         );
> >     | |_________^ the trait `kernel::fmt::Display` is not implemented for `MsgFunction`
> >     |
> >     = help: the following other types implement trait `kernel::fmt::Display`:
> >               &T
> >               Arc<T>
> >               Arguments<'_>
> >               BStr
> >               Box<T, A>
> >               CStr
> >               Chipset
> >               Class
> >             and 22 others
> >     = note: required for `kernel::fmt::Adapter<&MsgFunction>` to implement `core::fmt::Display`
> > note: required by a bound in `core::fmt::rt::Argument::<'_>::new_display`
> >    --> /usr/lib/rustlib/src/rust/library/core/src/fmt/rt.rs:113:27
> >     |
> > 113 |     pub fn new_display<T: Display>(x: &T) -> Argument<'_> {
> >     |                           ^^^^^^^ required by this bound in `Argument::<'_>::new_display`
> >     = note: this error originates in the macro `::core::format_args` which comes from the expansion of the macro `dev_dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
> >
> > error: aborting due to 3 previous errors
> >
> > For more information about this error, try `rustc --explain E0277`.
> >
> > Caused by commit
> >
> >   c5cf01ba8dfe ("rust: support formatting of foreign types")
> >
> > (I think) interacting with commits
> >
> >   38b7cc448a5b ("gpu: nova-core: implement Display for Spec")
> >   75f6b1de8133 ("gpu: nova-core: gsp: Add GSP command queue bindings and handling")
> >
> > from the drm-rust tree.
>
> I applied a patch to drm-rust-next that makes this error go away.
>
> Alice

Thanks for taking care of this!

Alexandre: the correct thing to do going forward is never to use
`core::fmt`; instead always use `kernel::fmt`.