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

[Alice Ryhl <aliceryhl@google.com>]

On Mon, Oct 27, 2025 at 09:11:31AM +0100, Uwe Kleine-König wrote:
> Hello Stephen,
> 
> thanks for your report (and creating next each day!)
> 
> On Mon, Oct 27, 2025 at 12:51:48PM +1100, Stephen Rothwell wrote:
> > After merging the pwm tree, today's linux-next build (x86_64 allmodconfig)
> > failed like this:
> > 
> > error[E0277]: the trait bound `core::result::Result<core::pin::Pin<Box<Th1520PwmPlatformDriver, Kmalloc>>, kernel::error::Error>: PinInit<Th1520PwmPlatformDriver, kernel::error::Error>` is not satisfied
> >    --> drivers/pwm/pwm_th1520.rs:331:10
> >     |
> > 331 |     ) -> Result<Pin<KBox<Self>>> {
> >     |          ^^^^^^^^^^^^^^^^^^^^^^^ unsatisfied trait bound
> >     |
> >     = help: the trait `PinInit<Th1520PwmPlatformDriver, kernel::error::Error>` is not implemented for `Result<Pin<Box<Th1520PwmPlatformDriver, Kmalloc>>, Error>`
> >             but trait `PinInit<core::pin::Pin<Box<Th1520PwmPlatformDriver, Kmalloc>>, kernel::error::Error>` is implemented for it
> >     = help: for that trait implementation, expected `core::pin::Pin<Box<Th1520PwmPlatformDriver, Kmalloc>>`, found `Th1520PwmPlatformDriver`
> > note: required by a bound in `kernel::platform::Driver::{synthetic#0}`
> >    --> rust/kernel/platform.rs:196:15
> >     |
> > 196 |     ) -> impl PinInit<Self, Error>;
> >     |               ^^^^^^^^^^^^^^^^^^^^ required by this bound in `Driver::{synthetic#0}`
> > 
> > error: aborting due to 1 previous error
> > 
> > For more information about this error, try `rustc --explain E0277`.
> > 
> > Caused by commit
> > 
> >   fb3957af9ec6 ("pwm: Add Rust driver for T-HEAD TH1520 SoC")
> > 
> > presumably interacting with something merged earlier in my tree.
> > If someone could provide me with an appropriate merge resolution, I will
> > apply it.
> 
> Having no relevant clue about Rust, I bisected that. The bisection points to
> 0242623384c7 ("rust: driver: let probe() return impl PinInit<Self, Error>").
> 
> Translating the changes that commit does to
> drivers/gpu/drm/nova/driver.rs for drivers/pwm/pwm_th1520.rs results in:
> 
> diff --git a/drivers/pwm/pwm_th1520.rs b/drivers/pwm/pwm_th1520.rs
> index 0ad38b78be85..dd554574adc8 100644
> --- a/drivers/pwm/pwm_th1520.rs
> +++ b/drivers/pwm/pwm_th1520.rs
> @@ -328,7 +328,7 @@ impl platform::Driver for Th1520PwmPlatformDriver {
>      fn probe(
>          pdev: &platform::Device<Core>,
>          _id_info: Option<&Self::IdInfo>,
> -    ) -> Result<Pin<KBox<Self>>> {
> +    ) -> impl PinInit<Self, Error> {
>          let dev = pdev.as_ref();
>          let request = pdev.io_request_by_index(0).ok_or(ENODEV)?;
>  
> @@ -365,7 +365,7 @@ fn probe(
>  
>          pwm::Registration::register(dev, chip)?;
>  
> -        Ok(KBox::new(Th1520PwmPlatformDriver, GFP_KERNEL)?.into())
> +        Ok(Th1520PwmPlatformDriver)
>      }
>  }
>  
> which builds again.

This merge resolution looks correct.

Alice