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

Alexandre Courbot
2025-11-17T11:19:49Z

Hi Stephen,
On Mon Nov 17, 2025 at 5:04 PM JST, 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

I could work around this with the following patch, but it looks terribly
wrong. In gpu.rs we need to implement core::fmt::Display (because of the
use of `write!`), but in fw.rs we need to implement
kernel::fmt::Display. It is not clear to me how the two interfaces are
supposed to interact.

Tamir, could you advise on the correct thing to do here?

diff --git a/drivers/gpu/nova-core/gpu.rs b/drivers/gpu/nova-core/gpu.rs
index 19755af6ad04..de924ffc0823 100644
--- a/drivers/gpu/nova-core/gpu.rs
+++ b/drivers/gpu/nova-core/gpu.rs
@@ -115,7 +115,7 @@ pub(crate) fn arch(&self) -> Architecture {
// Hence, replace with something like strum_macros derive(Display).
//
// For now, redirect to fmt::Debug for convenience.
-impl fmt::Display for Chipset {
+impl core::fmt::Display for Chipset {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "{self:?}")
}
@@ -169,7 +169,7 @@ fn from(boot0: regs::NV_PMC_BOOT_42) -> Self {
}
}

-impl fmt::Display for Revision {
+impl core::fmt::Display for Revision {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "{:x}.{:x}", self.major, self.minor)
}
diff --git a/drivers/gpu/nova-core/gsp/fw.rs b/drivers/gpu/nova-core/gsp/fw.rs
index 8deec5e0a1d4..53afdbfa9554 100644
--- a/drivers/gpu/nova-core/gsp/fw.rs
+++ b/drivers/gpu/nova-core/gsp/fw.rs
@@ -7,12 +7,12 @@
use r570_144 as bindings;

use core::{
- fmt,
ops::Range, //
};

use kernel::{
dma::CoherentAllocation,
+ fmt,
prelude::*,
ptr::{
Alignable,