Re: [PATCH v2 1/3] rust: add runtime PM support

[Alice Ryhl <aliceryhl@google.com>]

On Tue, Jul 21, 2026 at 05:34:02PM +0200, Beata Michalska wrote:
> +/// Runtime PM callbacks implemented by a driver.
> +///
> +/// Defines the [`PMOps`] trait and its corresponding [`bindings::dev_pm_ops`].
> +///
> +/// Each generated C callback recovers the Rust bus device from the raw
> +/// `struct device *`, borrows the registered runtime PM payload, and delegates
> +/// to the matching [`PMOps`] trait method.
> +///
> +/// # Safety
> +///
> +/// `PMContext::<T>::PM_OPS` must only be installed for devices whose concrete
> +/// bus type is `T::DeviceType`, and whose runtime PM registration data was
> +/// installed by [`Registration::new`] for the same `T`.
> +///
> +macro_rules! define_pm_ops {
> +    ($($name:ident $( : $desc:tt )? ),+ $(,)?) => {
> +        $( define_pm_callback!( @parse_desc $name $( $desc )?); )+
> +        define_pm_ops!(@common $( $name ), +);
> +    };
> +
> +    (@common $( $name:ident),+ ) => {
> +        /// Runtime PM callbacks implemented by a driver
> +        #[vtable]
> +        pub trait PMOps: Sized
> +        {
> +            /// Type of a bus device
> +            type DeviceType: AsBusDevice<device::Bound>;
> +            /// Type of the data associated with a PM transitions:
> +            type RuntimePayloadType: Send;
> +
> +            $(
> +                #[allow(missing_docs)]
> +                // Callback-specific docs are provided by the generated `dev_pm_ops`
> +                // contract on `PMOps`.
> +
> +                fn $name<'a>(
> +                    _dev:  &'a Self::DeviceType,
> +                    _payload: Option<Self::RuntimePayloadType>,
> +                ) -> Result<Option<Self::RuntimePayloadType>, (Option<Self::RuntimePayloadType>, Error)> {
> +                    build_error!(VTABLE_DEFAULT_ERROR)
> +                }
> +            )+
> +        }
> +        paste!(
> +            impl<'a, T:PMOps> PMContext<'a, T> {
> +                /// Driver-provided runtime PM operations.
> +                ///
> +                /// A driver implements this trait to handle runtime PM
> +                /// transitions for its device type.
> +                ///
> +                /// Each callback receives the device and the current payload.
> +                /// On success, it returns the payload to keep for the next
> +                /// transition. On failure, it returns the payload together
> +                /// with the error so the previous, or otherwise sane state
> +                /// can be preserved.
> +                pub const PM_OPS: bindings::dev_pm_ops = bindings::dev_pm_ops {
> +                    $( [<$name>]: if T::[<HAS_ $name:upper>] {
> +                        Some([<$name _callback>]::<T>)
> +                    } else {
> +                        None
> +                    }, )+
> +                    ..PMOPS_NONE
> +                };
> +            }
> +        );
> +    }
> +}

> +
> +define_pm_ops!(
> +    // PM state change
> +    runtime_suspend,
> +    runtime_resume,
> +);

I think using a macro to define this trait is overkill. Just write it
out:

pub trait PMOps: Sized {
    /// Type of a bus device
    type DeviceType: AsBusDevice<device::Bound>;
    /// Type of the data associated with a PM transitions:
    type RuntimePayloadType: Send;

    fn runtime_suspend<'a>(
        _dev:  &'a Self::DeviceType,
        _payload: Option<Self::RuntimePayloadType>,
    ) -> Result<Option<Self::RuntimePayloadType>, (Option<Self::RuntimePayloadType>, Error)> {
        build_error!(VTABLE_DEFAULT_ERROR)
    }

    fn runtime_resume<'a>(
        _dev:  &'a Self::DeviceType,
        _payload: Option<Self::RuntimePayloadType>,
    ) -> Result<Option<Self::RuntimePayloadType>, (Option<Self::RuntimePayloadType>, Error)> {
        build_error!(VTABLE_DEFAULT_ERROR)
    }
}

This is a lot easier to read.

Alice