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

On Tue, 21 Jul 2026 17:34:02 +0200
Beata Michalska <[email protected]> wrote:

> Add a Rust abstraction for Linux runtime PM, allowing Rust drivers to
> register runtime PM callbacks and use scoped runtime PM requests while
> retaining the behavior and guarantees of the underlying C PM core.
> 
> Runtime PM is managed through a registration object tied to the device
> lifetime. The registration stores the callback payload and 'ensures' that
> the registration, its `PMContext`, and the payload do not outlive the
> device. All that while `PMContext` holds a lifetime-annotated device reference
> so that runtime PM requests are made only while the device remains bound.
> 
> Drivers define runtime PM callbacks through the `PMOps` trait. The
> generated `dev_pm_ops` callbacks take the stored payload, pass ownership
> to the corresponding Rust callback, and store the returned payload for
> the next invocation. Each callback must return a valid payload,
> regardless of whether the power transition succeeds or not.
> 
> `PMContext` provides scoped helpers for common runtime PM operations:
> 
> - `ResumeScope` resumes the device for the lifetime of the scope.
> - `AwakeScope`  resumes the device and holds a runtime PM usage reference.
> - `RetainScope` increments the runtime PM usage count without resuming the
>   		device.
> 
> Each scope performs the corresponding inverse operation when dropped,
> according to the selected driver-defined profile.
> 
> The abstraction does not change the semantics of the C runtime PM API.
> Asynchronous requests may only queue work, non-waiting requests may fail
> instead of sleeping, and callbacks remain subject to the existing driver
> core rules.
> 
> The current implementation requires the PM registration and `PMOps`
> implementation to use the same type because callback dispatch interprets
> the stored registration data using that relationship. This requirement is
> not yet fully enforced by the type system.
> 
> Signed-off-by: Beata Michalska <[email protected]>
> ---
>  drivers/base/base.h             |    3 +
>  rust/bindings/bindings_helper.h |    1 +
>  rust/helpers/helpers.c          |    1 +
>  rust/helpers/pm_runtime.c       |   44 ++
>  rust/kernel/lib.rs              |    1 +
>  rust/kernel/pm.rs               | 1020 +++++++++++++++++++++++++++++++
>  6 files changed, 1070 insertions(+)
>  create mode 100644 rust/helpers/pm_runtime.c
>  create mode 100644 rust/kernel/pm.rs
> 
> diff --git a/drivers/base/base.h b/drivers/base/base.h
> index a19f4cda2c83..c49303e4a86a 100644
> --- a/drivers/base/base.h
> +++ b/drivers/base/base.h
> @@ -119,6 +119,9 @@ struct device_private {
>  	const struct device_driver *async_driver;
>  	char *deferred_probe_reason;
>  	struct device *device;
> +#ifdef CONFIG_RUST
> +	void *rust_private;
> +#endif
>  	u8 dead:1;
>  };
>  #define to_device_private_parent(obj)	\
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index 1124785e210b..78a9153c6a01 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
> @@ -77,6 +77,7 @@
>  #include <linux/pid_namespace.h>
>  #include <linux/platform_device.h>
>  #include <linux/pm_opp.h>
> +#include <linux/pm_runtime.h>
>  #include <linux/poll.h>
>  #include <linux/property.h>
>  #include <linux/pwm.h>
> diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
> index 4488a87223b9..14d93a5d8b1f 100644
> --- a/rust/helpers/helpers.c
> +++ b/rust/helpers/helpers.c
> @@ -76,6 +76,7 @@
>  #include "pci.c"
>  #include "pid_namespace.c"
>  #include "platform.c"
> +#include "pm_runtime.c"
>  #include "poll.c"
>  #include "processor.c"
>  #include "property.c"
> diff --git a/rust/helpers/pm_runtime.c b/rust/helpers/pm_runtime.c
> new file mode 100644
> index 000000000000..d0d71fcb0097
> --- /dev/null
> +++ b/rust/helpers/pm_runtime.c
> @@ -0,0 +1,44 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/pm_runtime.h>
> +
> +__rust_helper void rust_helper_pm_runtime_get_noresume(struct device *dev)
> +{
> +	pm_runtime_get_noresume(dev);
> +}
> +
> +__rust_helper void rust_helper_pm_runtime_put_noidle(struct device *dev)
> +{
> +	pm_runtime_put_noidle(dev);
> +}
> +
> +__rust_helper void rust_helper_pm_runtime_mark_last_busy(struct device *dev)
> +{
> +	pm_runtime_mark_last_busy(dev) ;
> +}
> +
> +__rust_helper bool rust_helper_pm_runtime_active(struct device *dev)
> +{
> +	return pm_runtime_active(dev);
> +}
> +
> +__rust_helper bool rust_helper_pm_runtime_suspended(struct device *dev)
> +{
> +	return pm_runtime_suspended(dev);
> +}
> +
> +__rust_helper void rust_helper_pm_suspend_ignore_children(struct device *dev,
> +							  bool enable)
> +{
> +	pm_suspend_ignore_children(dev, enable);
> +}
> +
> +__rust_helper int rust_helper_pm_runtime_set_active(struct device *dev)
> +{
> +	return pm_runtime_set_active(dev);
> +}
> +
> +__rust_helper int rust_helper_pm_runtime_set_suspended(struct device *dev)
> +{
> +	return pm_runtime_set_suspended(dev);
> +}
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index b72b2fbe046d..7e51e497e2f0 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -105,6 +105,7 @@
>  pub mod pci;
>  pub mod pid_namespace;
>  pub mod platform;
> +pub mod pm;
>  pub mod prelude;
>  pub mod print;
>  pub mod processor;
> diff --git a/rust/kernel/pm.rs b/rust/kernel/pm.rs
> new file mode 100644
> index 000000000000..b6a884fbe1ba
> --- /dev/null
> +++ b/rust/kernel/pm.rs
> @@ -0,0 +1,1020 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Rust Runtime Power Management abstraction.
> +//!
> +//! C header: [`include/linux/pm_runtime.h`](srctree/include/linux/pm_runtime.h)
> +
> +use crate::{
> +    bindings,
> +    device::{
> +        self,
> +        AsBusDevice, //
> +    },
> +    error::{
> +        to_result,
> +        VTABLE_DEFAULT_ERROR, //
> +    },
> +    macros::paste,
> +    prelude::*,
> +    sync::atomic::{
> +        ordering,
> +        Atomic, //
> +    },
> +    sync::Arc,
> +    types::ForeignOwnable, //
> +};
> +
> +use core::{
> +    cell::UnsafeCell,
> +    marker::PhantomData
> +};
> +
> +/// Runtime Power Management modes that determine how a particular PM
> +/// transition is to be carried out.
> +/// Corresponds to C Runtime PM flag argument bits:
> +/// - `RPM_ASYNC`
> +/// - `RPM_NOWAIT`
> +/// - `RPM_GET_PUT`
> +/// - `RPM_AUTO`
> +#[derive(Clone, Copy, PartialEq, Eq, Debug)]
> +struct Mode(u32);
> +
> +impl Mode {
> +    /// Synchronous PM operations - default.
> +    const SYNC: Mode = Mode(0);
> +    /// Allow asynchronous PM operations.
> +    const ASYNC: Mode = Mode(bindings::RPM_ASYNC);
> +    /// Do not wait for any pending requests to finish.
> +    const NOWAIT: Mode = Mode(bindings::RPM_NOWAIT);
> +    /// Acquire a runtime-PM usage reference.
> +    const ACQUIRE: Mode = Mode(bindings::RPM_GET_PUT);
> +    /// Use autosuspend.
> +    const AUTO: Mode = Mode(bindings::RPM_AUTO);
> +    /// Additional mode for devices supporting idle states.
> +    /// No counterpart.
> +    const IDLE: Mode = Mode(1 << 16);
> +
> +    const fn join(self, other: Self) -> Self {
> +        Self(self.0 | other.0)
> +    }
> +
> +    fn includes(self, other: Self) -> bool {
> +        (self.0 & other.0) != 0
> +    }
> +}
> +
> +impl core::ops::BitOr for Mode {
> +    type Output = Self;
> +    fn bitor(self, rhs: Self) -> Self::Output {
> +        Self(self.0 | rhs.0)
> +    }
> +}
> +
> +impl core::ops::BitAnd for Mode {
> +    type Output = Self;
> +    fn bitand(self, rhs: Self) -> Self::Output {
> +        Self(self.0 & rhs.0)
> +    }
> +}
> +
> +impl core::ops::Not for Mode {
> +    type Output = Self;
> +    fn not(self) -> Self::Output {
> +        Self(!self.0)
> +    }
> +}
> +
> +impl From<Mode> for core::ffi::c_int {
> +    #[inline]
> +    fn from(mode: Mode) -> core::ffi::c_int {
> +        mode.0 as core::ffi::c_int
> +    }
> +}
> +
> +/// Utility macro for combining multiple request modes
> +macro_rules! mode {
> +    ($mode:expr $(, $args:expr)+ $(,)?) => {{
> +        let mut new_mode = $mode;
> +        $( new_mode = new_mode.join($args); )+
> +        new_mode
> +    }};
> +}
> +
> +/// Device's runtime power management status
> +#[repr(i32)]
> +pub enum RuntimePMState {
> +    /// Runtime PM has not been initialized for this device yet.
> +    UNKNOWN = bindings::rpm_status_RPM_INVALID,
> +    /// The device is expected to be runtime active and in it's normal operating state
> +    RESUMED = bindings::rpm_status_RPM_ACTIVE,
> +    /// The device is expected to be suspended, unavailable for normal operations
> +    SUSPENDED = bindings::rpm_status_RPM_SUSPENDED,
> +}
> +
> +/// Runtime power transition scope.
> +pub struct Scope<'a, Tag> {
> +    dev: &'a device::Device<device::Bound>,
> +    mode: Mode,
> +    _tag: PhantomData<Tag>,
> +}
> +
> +/// Device resumed without incrementing the device's usage count
> +pub struct Resume;
> +/// Device resumed with the device's usage count being incremented
> +pub struct Awake;
> +/// Device with increased usage reference
> +pub struct Retain;
> +
> +/// Resumes the device without acquiring the usage reference.
> +/// Note: This does not guarantee the device will be kept active
> +/// for the lifetime of the scope due to potential pending/incoming
> +/// suspend requests.
> +///
> +/// On drop:
> +/// - If `Mode::IDLE`, calls `__pm_runtime_idle()`:
> +///   triggers idle notification before attempting to suspend
> +/// - If `Mode::AUTO`, marks last busy then calls `__pm_runtime_suspend()`.
> +/// - Otherwise calls `__pm_runtime_suspend()`.
> +///
> +/// The guard must be dropped from a context matching the requested transition
> +/// mode: sync vs async.
> +#[must_use = "dropping this guard issues the matching runtime PM release request"]
> +pub struct ResumeScope<'a>(Scope<'a, Resume>);
> +
> +/// Acquires a runtime-PM usage reference and keeps the device powered.
> +///
> +/// Requires `Mode::ACQUIRE`. Drop behavior matches `ResumeScope`.
> +/// The guard must be dropped from a context matching the requested transition
> +/// mode: sync vs async.
> +#[must_use = "dropping this guard releases its runtime PM hold"]
> +pub struct AwakeScope<'a>(Scope<'a, Awake>);
> +
> +/// Prevents the device from getting suspended by holding the usage reference
> +/// count.
> +///
> +/// On drop, calls `pm_runtime_put_noidle()`.
> +#[must_use = "dropping this guard releases its runtime PM hold"]
> +pub struct RetainScope<'a>(Scope<'a, Retain>);
> +
> +impl<'a> ResumeScope<'a> {
> +    fn new(dev: &'a device::Device<device::Bound>, mode: Mode) -> Result<Self> {
> +        if mode.includes(Mode::ACQUIRE) {
> +            // Mode::ACQUIRE is intended to be used with Awake scope
> +            // Avoid mixing the modes.
> +            return Err(EINVAL);
> +        }
> +
> +        // Mode::IDLE is internal so strip it of before passing further
> +        Request::resume(dev, mode & !Mode::IDLE).map(|()| {
> +            Self(Scope::<Resume> {
> +                dev,
> +                mode,
> +                _tag: PhantomData,
> +            })
> +        })
> +    }
> +
> +    fn release_inner(&self) -> Result {
> +        let scope_mode = self.0.mode & !Mode::IDLE;
> +
> +        match self.0.mode {
> +            mode if mode.includes(Mode::IDLE) => {
> +                Request::idle(self.0.dev, scope_mode & (Mode::ASYNC | Mode::NOWAIT))
> +            }
> +            mode if mode.includes(Mode::AUTO) => {
> +                Request::mark_last_busy(self.0.dev);
> +                Request::suspend(self.0.dev, scope_mode)
> +            }
> +            _ => Request::suspend(self.0.dev, scope_mode),
> +        }
> +    }
> +
> +    /// Explicitly release the scope
> +    /// This should be used in favor of regular drop
> +    /// when error handling is required.
> +    pub fn release(self) -> Result {
> +        let result = self.release_inner();
> +        core::mem::forget(self);
> +        result
> +    }
> +}
> +
> +impl<'a> Drop for ResumeScope<'a> {
> +    fn drop(&mut self) {
> +        let _ = self.release_inner();
> +    }
> +}
> +
> +impl<'a> AwakeScope<'a> {
> +    fn new(dev: &'a device::Device<device::Bound>, mode: Mode) -> Result<Self> {
> +        if !mode.includes(Mode::ACQUIRE) {
> +            return Err(EINVAL);
> +        }
> +        // Mode::IDLE is internal so strip it of before passing further
> +        Request::resume(dev, mode & !Mode::IDLE)
> +            .inspect_err(|_| Request::put_noidle(dev))
> +            .map(|()| {
> +                Self(Scope::<Awake> {
> +                    dev,
> +                    mode,
> +                    _tag: PhantomData,
> +                })
> +            })
> +    }
> +
> +    fn release_inner(&self) -> Result {
> +        let scope_mode = self.0.mode & !Mode::IDLE;
> +        match self.0.mode {
> +            mode if mode.includes(Mode::IDLE) => Request::idle(self.0.dev, scope_mode),
> +            mode if mode.includes(Mode::AUTO) => {
> +                Request::mark_last_busy(self.0.dev);
> +                Request::suspend(self.0.dev, scope_mode)
> +            }
> +            _ => Request::idle(self.0.dev, scope_mode),
> +        }
> +    }
> +
> +    /// Explicitly release the scope
> +    /// This should be used in favor of regular drop
> +    /// when error handling is required.
> +    pub fn release(self) -> Result {
> +        let result = self.release_inner();
> +        core::mem::forget(self);
> +        result
> +    }
> +}
> +
> +impl<'a> Drop for AwakeScope<'a> {
> +    fn drop(&mut self) {
> +        let _ = self.release_inner();
> +    }
> +}
> +
> +impl<'a> RetainScope<'a> {
> +    fn new(dev: &'a device::Device<device::Bound>) -> Result<Self> {
> +        Request::get_noresume(dev);
> +        Ok(Self(Scope::<Retain> {
> +            dev,
> +            mode: Mode(0),
> +            _tag: PhantomData,
> +        }))
> +    }
> +
> +    fn try_new(dev: &'a device::Device<device::Bound>) -> Result<Self> {
> +        Request::get_if_active(dev)?;
> +        Ok(Self(Scope::<Retain> {
> +            dev,
> +            mode: Mode(0),
> +            _tag: PhantomData,
> +        }))
> +    }
> +
> +    fn release_inner(&self) {
> +        Request::put_noidle(self.0.dev);
> +    }
> +
> +    /// Explicitly release the scope
> +    /// This should be used in favor of regular drop
> +    /// when error handling is required.
> +    pub fn release(self) -> Result {
> +        self.release_inner();
> +        core::mem::forget(self);
> +        Ok(())
> +    }
> +}
> +
> +impl<'a> Drop for RetainScope<'a> {
> +    fn drop(&mut self) {
> +        self.release_inner();
> +    }
> +}
> +
> +/// Runtime PM helpers - wrappers around C runtime PM interface.
> +/// All methods require a reference to a bound device.
> +struct Request;
> +
> +#[cfg(CONFIG_PM)]
> +impl Request {
> +    #[inline]
> +    fn active(dev: &device::Device<device::Bound>) -> bool {
> +        // SAFETY: `dev.as_raw()` must provide a valid pointer to
> +        // `struct device` for the duration of the call.
> +        // The `Device<Bound>` reference provides that guarantee.
> +        unsafe { bindings::pm_runtime_active(dev.as_raw()) }
> +    }
> +
> +    #[inline]
> +    fn suspended(dev: &device::Device<device::Bound>) -> bool {
> +        // SAFETY: `dev.as_raw()` must provide a valid pointer to
> +        // `struct device` for the duration of the call.
> +        // The `Device<Bound>` reference provides that guarantee.
> +        unsafe { bindings::pm_runtime_suspended(dev.as_raw()) }
> +    }
> +
> +    #[inline]
> +    fn resume(dev: &device::Device<device::Bound>, mode: Mode) -> Result {
> +        // SAFETY: `dev.as_raw()` must provide a valid pointer to
> +        // `struct device` for the duration of the call.
> +        // The `Device<Bound>` reference provides that guarantee.
> +        to_result(unsafe { bindings::__pm_runtime_resume(dev.as_raw(), mode.into()) })
> +    }
> +
> +    #[inline]
> +    fn idle(dev: &device::Device<device::Bound>, mode: Mode) -> Result {
> +        // SAFETY: `dev.as_raw()` must provide a valid pointer to
> +        // `struct device` for the duration of the call.
> +        // The `Device<Bound>` reference provides that guarantee.
> +        to_result(unsafe { bindings::__pm_runtime_idle(dev.as_raw(), mode.into()) })
> +    }
> +
> +    #[inline]
> +    fn mark_last_busy(dev: &device::Device<device::Bound>) {
> +        // SAFETY: `dev.as_raw()` must provide a valid pointer to
> +        // `struct device` for the duration of the call.
> +        // The `Device<Bound>` reference provides that guarantee.
> +        unsafe {
> +            bindings::pm_runtime_mark_last_busy(dev.as_raw());
> +        }
> +    }
> +
> +    #[inline]
> +    fn suspend(dev: &device::Device<device::Bound>, mode: Mode) -> Result {
> +        // SAFETY: `dev.as_raw()` must provide a valid pointer to
> +        // `struct device` for the duration of the call.
> +        // The `Device<Bound>` reference provides that guarantee.
> +        to_result(unsafe { bindings::__pm_runtime_suspend(dev.as_raw(), mode.into()) })
> +    }
> +
> +    #[inline]
> +    fn get_if_active(dev: &device::Device<device::Bound>) -> Result {
> +        // SAFETY: `dev.as_raw()` must provide a valid pointer to
> +        // `struct device` for the duration of the call.
> +        // The `Device<Bound>` reference provides that guarantee.
> +        match unsafe { bindings::pm_runtime_get_if_active(dev.as_raw()) } {
> +            ret if ret < 0 => Err(Error::from_errno(ret)),
> +            0 => Err(EAGAIN),
> +            _ => Ok(()),
> +        }
> +    }
> +
> +    #[inline]
> +    fn runtime_enable(dev: &device::Device<device::Bound>) {
> +        // SAFETY: `dev.as_raw()` must provide a valid pointer to
> +        // `struct device` for the duration of the call.
> +        // The `Device<Bound>` reference provides that guarantee.
> +        unsafe { bindings::pm_runtime_enable(dev.as_raw()) }
> +    }
> +
> +    #[inline]
> +    fn runtime_disable(dev: &device::Device<device::Bound>) {
> +        // SAFETY: `dev.as_raw()` must provide a valid pointer to
> +        // `struct device` for the duration of the call.
> +        // The `Device<Bound>` reference provides that guarantee.
> +        unsafe { bindings::__pm_runtime_disable(dev.as_raw(), true) };
> +    }

What happens when you call these twice i.e. runtime_enable() when it's already
enabled or runtime_disable() when it's already disabled?

> +}
> +
> +#[cfg(not(CONFIG_PM))]
> +impl Request {
> +    #[inline]
> +    fn active(dev: &device::Device<device::Bound>) -> bool {
> +        true
> +    }
> +
> +    #[inline]
> +    fn suspended(dev: &device::Device<device::Bound>) -> bool {
> +        false
> +    }
> +
> +    #[inline]
> +    fn resume(_dev: &device::Device<device::Bound>, _mode: Mode) -> Result {
> +        Ok(())
> +    }
> +
> +    #[inline]
> +    fn idle(_dev: &device::Device<device::Bound>, _mode: Mode) -> Result {
> +        Err(ENOSYS)
> +    }
> +
> +    #[inline]
> +    fn mark_last_busy(_dev: &device::Device<device::Bound>) {}
> +
> +    #[inline]
> +    fn suspend(_dev: &device::Device<device::Bound>, _mode: Mode) -> Result {
> +        Err(ENOSYS)
> +    }
> +
> +    #[inline]
> +    fn get_if_active(dev: &device::Device<device::Bound>) -> Result {
> +        Err(EINVAL)
> +    }
> +
> +    #[inline]
> +    fn runtime_enable(_dev: &device::Device<device::Bound>) {}
> +
> +    #[inline]
> +    fn runtime_disable(dev: &device::Device<device::Bound>) {}
> +}
> +
> +impl Request {
> +    #[inline]
> +    fn get_noresume(dev: &device::Device<device::Bound>) {
> +        // SAFETY: `dev.as_raw()` must provide a valid pointer to
> +        // `struct device` for the duration of the call.
> +        // The `Device<Bound>` reference provides that guarantee.
> +        unsafe { bindings::pm_runtime_get_noresume(dev.as_raw()) };
> +    }
> +
> +    #[inline]
> +    fn put_noidle(dev: &device::Device<device::Bound>) {
> +        // SAFETY: `dev.as_raw()` must provide a valid pointer to
> +        // `struct device` for the duration of the call.
> +        // The `Device<Bound>` reference provides that guarantee.
> +        unsafe { bindings::pm_runtime_put_noidle(dev.as_raw()) };
> +    }
> +
> +    #[allow(unused)]
> +    #[inline]
> +    fn mark_active(dev: &device::Device<device::Bound>) -> Result {
> +        to_result(
> +            // SAFETY: `dev.as_raw()` must provide a valid pointer to
> +            // `struct device` for the duration of the call.
> +            // The `Device<Bound>` reference provides that guarantee.
> +            unsafe { bindings::pm_runtime_set_active(dev.as_raw()) },
> +        )
> +    }
> +
> +    #[allow(unused)]
> +    #[inline]
> +    fn mark_suspended(dev: &device::Device<device::Bound>) -> Result {
> +        to_result(
> +            // SAFETY: `dev.as_raw()` must provide a valid pointer to
> +            // `struct device` for the duration of the call.
> +            // The `Device<Bound>` reference provides that guarantee.
> +            unsafe { bindings::pm_runtime_set_suspended(dev.as_raw()) },
> +        )
> +    }
> +}
> +
> +/// Common runtime PM callback entry point
> +///
> +/// The generated extern "C" callbacks call into this helper with the raw
> +/// `struct device *` provided by the PM core. It rebuilds the Rust device
> +/// reference, retrieves the device's PM registration data and performs
> +/// handoff to corresponding driver callback.
> +fn runtime_pm_callback<T, F>(dev: *mut bindings::device, cb: F) -> Result
> +where
> +    T: PMOps,
> +    F: FnOnce(
> +        &<T as PMOps>::DeviceType,
> +        Option<<T as PMOps>::RuntimePayloadType>,
> +    ) -> Result<
> +        Option<<T as PMOps>::RuntimePayloadType>,
> +        (Option<<T as PMOps>::RuntimePayloadType>, Error),
> +    >,
> +{
> +    let dev: &device::Device<device::Bound>  =
> +             // SAFETY: `dev` is provided by the PM core and remains
> +             // valid for the duration of the callback.
> +            unsafe { device::Device::from_raw(dev) };
> +
> +    // SAFETY: `dev` is provided by the PM core and remains
> +    // valid for the duration of the callback.
> +    let ptr = unsafe { (*(*dev.as_raw()).p).rust_private };
> +
> +    if ptr.is_null() {
> +        return Err(ENODEV);
> +    }
> +
> +    // SAFETY: The runtime PM callback can only be triggered for bound device
> +    // and once the runtime PM is enabled.
> +    // `rust_private` is guaranteed to be valid and points to
> +    // associated RegistrationData<T> type object at least for the duration
> +    // of this call.
> +    let payload: Pin<&RegistrationData<'_, T>> =
> +        unsafe { <Pin<KBox<RegistrationData<'_, T>>> as ForeignOwnable>::borrow(ptr) };
> +
> +    let pm_dev: &T::DeviceType =
> +        // SAFETY: The generated `dev_pm_ops` for `T` is installed on devices whose
> +        // bus-specific type is `T::DeviceType`. Therefore the base `Device<Bound>`
> +        // passed by the PM core is embedded in a valid `T::DeviceType`; the
> +        // `AsBusDevice` implementation supplies the correct offset for this cast.
> +        unsafe { T::DeviceType::from_device(dev) };
> +
> +    payload.data.transition(|payload| cb(pm_dev, payload))
> +}
> +
> +/// Defines generated C runtime PM callback.
> +///
> +/// This macro generates the corresponding `unsafe extern "C"` function for
> +/// requested PM operation and forwards it to [`runtime_pm_callback`].
> +///
> +/// # Safety
> +///
> +/// The generated function may only be installed in a `dev_pm_ops` table for a
> +/// device whose PM registration data was created by `Registration<T>`. In other
> +/// words, the type parameter `T` used for the callback table must match the
> +/// type parameter `T` used for the stored `RegistrationData<T>`.
> +///
> +/// The PM registration must keep the stored registration data alive and pinned
> +/// until runtime PM is disabled and all in-flight PM callbacks have completed.
> +macro_rules! define_pm_callback {
> +    (@parse_desc $name:ident) => { define_pm_callback!(@default $name); };
> +    (@default $name:ident) => {
> +        paste!(
> +          /// Generated runtime PM callback.
> +          ///
> +          /// # Safety
> +          ///
> +          /// `dev` must be a valid `struct device *` supplied by the PM core for a device
> +          /// whose runtime PM callbacks and PM registration data were both created
> +          /// for `T`.
> +            unsafe extern "C" fn [<$name _callback>]<'a, T:PMOps>(
> +                dev: *mut bindings::device
> +            ) -> core::ffi::c_int
> +                where
> +                    <T as PMOps>::DeviceType: 'a
> +            {
> +               runtime_pm_callback::<T, _>(dev,T::$name).map(|_| 0).unwrap_or_else(|e| e.to_errno())
> +            }
> +        );
> +
> +    };
> +}
> +
> +/// SAFETY:
> +/// bindings::dev_pm_ops is #[repr(C)], implements Default
> +/// and the struct itself is all nullable function pointers.
> +/// There is no padding and all zero bit-pattern is valid
> +///
> +const PMOPS_NONE: bindings::dev_pm_ops =
> +    unsafe { core::mem::MaybeUninit::<bindings::dev_pm_ops>::zeroed().assume_init() };
> +
> +/// Runtime PM callbacks implemented by a driver.
> +///
> +/// Defines the [`PMOps`] trait and its corresponding [`bindings::dev_pm_ops`].
> +///
> +/// Each generated C callback recovers the Rust bus device from the raw
> +/// `struct device *`, borrows the registered runtime PM payload, and delegates
> +/// to the matching [`PMOps`] trait method.
> +///
> +/// # Safety
> +///
> +/// `PMContext::<T>::PM_OPS` must only be installed for devices whose concrete
> +/// bus type is `T::DeviceType`, and whose runtime PM registration data was
> +/// installed by [`Registration::new`] for the same `T`.
> +///
> +macro_rules! define_pm_ops {
> +    ($($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
> +                };
> +            }
> +        );
> +    }
> +}
> +
> +/// RAII guard for ongoing runtime PM payload transition.
> +///
> +/// For most of the callbacks this guard is not necessairly needed as
> +/// the callbacks themselves are being serialized by the runtime PM C code.
> +/// Still, some like runtime_idle are exempt ftom that.
> +#[allow(unused)]
> +struct PayloadGuard<'a> {
> +    busy: &'a Atomic<bool>,
> +}
> +
> +impl Drop for PayloadGuard<'_> {
> +    fn drop(&mut self) {
> +        self.busy.store(false, ordering::Release);
> +    }
> +}
> +
> +struct PMPayload<P> {
> +    in_flight: Atomic<bool>,
> +    inner: UnsafeCell<Option<P>>,
> +}
> +
> +impl<P> PMPayload<P> {
> +    /// Attempts to acquire exclusive access to the runtime PM payload.
> +    ///
> +    /// Returns `EBUSY` if another runtime PM callback is already transitioning the
> +    /// payload.
> +    fn acquire(&self) -> Result<PayloadGuard<'_>> {
> +        self.in_flight
> +            .cmpxchg(false, true, ordering::Acquire)
> +            .map_err(|_| EBUSY)?;
> +        Ok(PayloadGuard {
> +            busy: &self.in_flight,
> +        })
> +    }
> +
> +    /// Runs a runtime PM transition with exclusive access to the stored payload.
> +    ///
> +    /// This method acquires the in-flight guard, temporarily takes the payload out
> +    /// of storage The closure must return the payload that should be stored
> +    /// for the next transition.
> +    ///
> +    /// On success, the returned payload replaces the previous payload. On failure,
> +    /// the closure returns the payload together with the error, and that payload is
> +    /// restored before the error is propagated.
> +    ///
> +    /// Returns `EBUSY` if another runtime PM transition is already in progress.
> +    fn transition(
> +        &self,
> +        f: impl FnOnce(Option<P>) -> Result<Option<P>, (Option<P>, Error)>,
> +    ) -> Result {
> +        let _guard = self.acquire()?;
> +        // SAFETY: Holding `_guard` means this callback successfully changed
> +        // `in_flight` from false to true. No other caller can hold a `PayloadGuard`
> +        // until `_guard` is dropped, so this function has exclusive access to `inner`.
> +        let slot = unsafe { &mut *self.inner.get() };
> +
> +        let payload = slot.take();
> +
> +        match f(payload) {
> +            Ok(new_payload) => {
> +                *slot = new_payload;
> +                Ok(())
> +            }
> +            Err((old_payload, err)) => {
> +                *slot = old_payload;
> +                Err(err)
> +            }
> +        }
> +    }
> +}
> +
> +// SAFETY: Although PMPayload's `inner` is an `UnsafeCell`, it is only accessed
> +// after `in_flight` has been acquired. The atomic flag serializes all mutable
> +// access to the payload, and `PayloadGuard` clears the flag when the access ends.
> +unsafe impl<P: Send> Sync for PMPayload<P> {}
> +
> +struct PMContextInner<'a, T: PMOps> {
> +    dev: &'a device::Device<device::Bound>,
> +    /// Optional driver-selected runtime PM request PMProfiles.
> +    ///
> +    /// Set of runtime PM predefined PMProfiles that can be used by the driver
> +    /// when requesting a PM transition. This might be useful when a driver
> +    /// has several different PM usage patterns.
> +    /// See [PMProfile] for more details.
> +    profiles: KVec<PMProfile>,
> +    /// Set of PM config options applied for associated device.
> +    configs: KVec<PMConfig>,
> +    _marker: PhantomData<T>,
> +}
> +
> +/// Runtime PM context tied to a device.
> +pub struct PMContext<'a, T: PMOps> {
> +    // Preferably, PMContext could be shared via borrowed reference over
> +    // a pm Registraion's lifetime but that bares complications on its own
> +    // when the context needs to be shared across different Registration types.
> +    inner: Arc<PMContextInner<'a, T>>,
> +}
> +
> +impl<'a, T: PMOps> PMContext<'a, T> {
> +    /// Enable runtime PM
> +    pub fn enable(&self, state: RuntimePMState) -> Result {
> +        Self::apply_config(self.inner.dev, &self.inner.configs);
> +        match state {
> +            RuntimePMState::RESUMED => Request::mark_active(self.inner.dev),
> +            RuntimePMState::SUSPENDED => Request::mark_suspended(self.inner.dev),
> +            _ => Err(EINVAL),
> +        }?;
> +        Request::runtime_enable(self.inner.dev);
> +        Ok(())
> +    }
> +    /// Disable runtime PM
> +    pub fn disable(&self) -> Result {
> +        Self::apply_config(self.inner.dev, &[PMConfig::AutoSuspend(false)]);
> +        Request::runtime_disable(self.inner.dev);
> +        Ok(())
> +    }
> +
> +    /// Returns whether the runtime PM state is active.
> +    #[inline]
> +    pub fn active(&self) -> bool {
> +        Request::active(self.inner.dev)
> +    }
> +
> +    /// Returns whether the runtime PM state is suspended.
> +    #[inline]
> +    pub fn suspended(&self) -> bool {
> +        Request::suspended(self.inner.dev)
> +    }
> +
> +    /// Creates a `ResumeScope` for the given PMProfile.
> +    #[inline]
> +    pub fn resume(&self, profile: PMProfile) -> Result<ResumeScope<'a>> {
> +        ResumeScope::new(self.inner.dev, profile.0)
> +    }
> +
> +    /// Creates an `AwakeScope` for the given PMProfile.
> +    /// Note that for ASYNC request this does not guarantee
> +    /// the device has been resumed at the time this funtion returns.
> +    #[inline]
> +    pub fn get(&self, profile: PMProfile) -> Result<AwakeScope<'a>> {
> +        AwakeScope::new(self.inner.dev, profile.0 | Mode::ACQUIRE)
> +    }
> +
> +    /// Creates a `RetainScope` for this device.
> +    pub fn hold(&self) -> Result<RetainScope<'a>> {
> +        RetainScope::new(self.inner.dev)
> +    }
> +
> +    /// Creates a `RetainScope` for an active device.
> +    pub fn try_hold_active(&self) -> Result<RetainScope<'a>> {
> +        RetainScope::try_new(self.inner.dev)
> +    }
> +
> +    /// Runs a closure while holding a `ResumeScope`.
> +    pub fn with_resume<R>(&self, profile: PMProfile, f: impl FnOnce() -> Result<R>) -> Result<R> {
> +        if profile.0.includes(Mode::ASYNC) {
> +            return Err(EINVAL);
> +        }
> +        let _scope = self.resume(profile)?;
> +        f()
> +    }
> +    /// Runs a closure while holding an `AwakeScope`.
> +    pub fn with_get<R>(&self, profile: PMProfile, f: impl FnOnce() -> Result<R>) -> Result<R> {
> +        if profile.0.includes(Mode::ASYNC) {
> +            return Err(EINVAL);
> +        }
> +        let _scope = self.get(profile)?;
> +        f()
> +    }
> +
> +    /// Runs a closure while holding a `RetainScope`.
> +    pub fn with_hold<R>(&self, f: impl FnOnce() -> Result<R>) -> Result<R> {
> +        let _scope = self.hold()?;
> +        f()
> +    }
> +
> +    /// Applies runtime PM configuration options.
> +    ///
> +    /// Options are applied in the order provided. The currently supported
> +    /// options do not report per-option failures.
> +    fn apply_config(dev: &device::Device<device::Bound>, opts: &[PMConfig]) {
> +        #[cfg(not(CONFIG_PM))]
> +        let _ = opts;
> +        let _ = dev;
> +        #[cfg(CONFIG_PM)]
> +        for opt in opts {
> +            match opt {
> +                // SAFETY: `self.dev` is a valid `&ARef<Device>`, so the underlying `Device` is
> +                // guaranteed to be alive and `as_raw()` yields a valid pointer for the
> +                // duration of this call.
> +                PMConfig::IgnoreChildren(v) => unsafe {
> +                    bindings::pm_suspend_ignore_children(dev.as_raw(), *v)
> +                },
> +                // SAFETY: `self.dev` is a valid `&ARef<Device>`, so the underlying `Device` is
> +                // guaranteed to be alive and `as_raw()` yields a valid pointer for the
> +                // duration of this call.
> +                PMConfig::NoCallbacks => unsafe { bindings::pm_runtime_no_callbacks(dev.as_raw()) },
> +                // SAFETY: `self.dev` is a valid `&ARef<Device>`, so the underlying `Device` is
> +                // guaranteed to be alive and `as_raw()` yields a valid pointer for the
> +                // duration of this call.
> +                PMConfig::IrqSafe => unsafe { bindings::pm_runtime_irq_safe(dev.as_raw()) },
> +                // SAFETY: `self.dev` is a valid `&ARef<Device>`, so the underlying `Device` is
> +                // guaranteed to be alive and `as_raw()` yields a valid pointer for the
> +                // duration of this call.
> +                PMConfig::AutoSuspend(v) => unsafe {
> +                    bindings::__pm_runtime_use_autosuspend(dev.as_raw(), *v);
> +                },
> +                // SAFETY: `self.dev` is a valid `&ARef<Device>`, so the underlying `Device` is
> +                // guaranteed to be alive and `as_raw()` yields a valid pointer for the
> +                // duration of this call.
> +                PMConfig::AutoSuspendDelay(v) => unsafe {
> +                    bindings::pm_runtime_set_autosuspend_delay(dev.as_raw(), *v as i32);
> +                    bindings::__pm_runtime_use_autosuspend(dev.as_raw(), true);
> +                },
> +            }
> +        }
> +    }
> +
> +    /// Get a borrowed reference to PM profiles asociated wiht the PM context
> +    pub fn profiles(&self) -> &[PMProfile] {
> +        &self.inner.profiles
> +    }
> +
> +    /// Get a borrowed reference to PM configs asociated wiht the PM context
> +    pub fn configs(&self) -> &[PMConfig] {
> +        &self.inner.configs
> +    }
> +}
> +
> +// Preferably, PMContext could be shared via borrowed reference over
> +// a pm Registraion's lifetime but that bares complications on its own
> +// when the context needs to be shared across different Registration types.
> +impl<T: PMOps> Clone for PMContext<'_, T> {
> +    fn clone(&self) -> Self {
> +        Self {
> +            inner: self.inner.clone(),
> +        }
> +    }
> +}
> +
> +define_pm_ops!(
> +    // PM state change
> +    runtime_suspend,
> +    runtime_resume,
> +);
> +
> +/// Runtime PM request PMProfile.
> +pub struct PMProfile(Mode);
> +
> +impl PMProfile {
> +    /// Creates a PMProfile with default SYNC mode set.
> +    pub const fn new() -> Self {
> +        Self(Mode::SYNC)
> +    }
> +    /// /Enables async PM operations for this PMProfile.
> +    pub const fn r#async(self) -> Self {
> +        Self(mode!(self.0, Mode::ASYNC))
> +    }
> +    /// Use autosuspend
> +    pub const fn auto(self) -> Self {
> +        Self(mode!(self.0, Mode::AUTO))
> +    }
> +    /// Requests idle handling for this PMProfile.
> +    pub const fn idle(self) -> Self {
> +        Self(mode!(self.0, Mode::IDLE))
> +    }
> +    /// Do not wait for concurrent requests to finish.
> +    pub const fn nowait(self) -> Self {
> +        Self(mode!(self.0, Mode::NOWAIT))
> +    }
> +}
> +
> +impl Default for PMProfile {
> +    fn default() -> Self {
> +        Self::new()
> +    }
> +}
> +
> +/// Configuration knobs for runtime PM.
> +pub enum PMConfig {
> +    /// Ignore child devices when suspending.
> +    IgnoreChildren(bool),
> +    /// Disable runtime PM callbacks.
> +    NoCallbacks,
> +    /// Mark device as IRQ-safe for runtime PM.
> +    IrqSafe,
> +    /// Enable or disable autosuspend.
> +    AutoSuspend(bool),
> +    /// Set autosuspend delay (milliseconds).
> +    AutoSuspendDelay(u32),
> +}
> +
> +/// Runtime PM data stored within the `struct device_private' during
> +/// runtime PM registration.
> +///
> +/// The data is associated with PM transitions and it's conceptually owned
> +/// by the Registration itself.
> +///
> +#[repr(C)]
> +#[pin_data]
> +struct RegistrationData<'a, T: PMOps> {
> +    #[pin]
> +    data: PMPayload<T::RuntimePayloadType>,
> +    _marker: PhantomData<&'a mut ()>,
> +}
> +
> +/// Runtime PM registration for a device.
> +///
> +/// A `Registration` installs the runtime PM payload used by the
> +/// generated [`PMOps`] callbacks and owns the corresponding teardown.
> +///
> +/// Dropping the registration disables runtime PM, waits for in-flight runtime PM
> +/// callbacks to complete, and then removes the stored registration data.
> +pub struct Registration<'a, T: PMOps> {
> +    ctx: PMContext<'a, T>,
> +}
> +
> +impl<'a, T: PMOps> Registration<'a, T> {
> +    /// Creates a runtime PM registration for `dev`.
> +    ///
> +    /// The provided profiles and configuration are stored in the associated
> +    /// [`PMContext`]. The optional `payload` is stored as a Registration data
> +    /// and is used to service PM transitions.
> +    ///
> +    /// The device must use the callback table generated for the same `T`.
> +    pub fn new(
> +        dev: &'a device::Device<device::Core<'_>>,
> +        profiles: Option<KVec<PMProfile>>,
> +        configs: Option<KVec<PMConfig>>,
> +        payload: Option<T::RuntimePayloadType>,
> +    ) -> Result<Self> {
> +        let payload = KBox::pin_init(
> +            RegistrationData::<T> {
> +                data: PMPayload {
> +                    in_flight: Atomic::new(false),
> +                    inner: UnsafeCell::new(payload),
> +                },
> +                _marker: PhantomData,
> +            },
> +            GFP_KERNEL,
> +        )?;
> +
> +        let inner_ctx = Arc::new(
> +            PMContextInner {
> +                dev,
> +                profiles: profiles.unwrap_or_default(),
> +                configs: configs.unwrap_or_default(),
> +                _marker: PhantomData,
> +            },
> +            GFP_KERNEL,
> +        )?;
> +
> +        // SAFETY: `dev` is a live `Device<Core>`, so its raw `struct device` pointer is
> +        // valid for the duration of this call. The payload allocation is converted into
> +        // a foreign pointer and owned by this `Registration` until `Drop` clears
> +        // `rust_private` and reconstructs the `KBox`.
> +        unsafe {
> +            let ptr = (*(*dev.as_raw()).p).rust_private;
> +            if !ptr.is_null() {
> +                return Err(EBUSY);
> +            }
> +            (*(*dev.as_raw()).p).rust_private = payload.into_foreign();
> +        }
> +
> +        Ok(Self {
> +            ctx: PMContext { inner: inner_ctx },
> +        })
> +    }
> +    /// Returns the runtime PM context associated with this registration.
> +    pub fn ctx(&self) -> &PMContext<'a, T> {
> +        &self.ctx
> +    }
> +}
> +
> +impl<'a, T: PMOps> Drop for Registration<'a, T> {
> +    fn drop(&mut self) {
> +        // SAFETY: `self.ctx.inner.dev` is the device this registration was
> +        // created for. Runtime PM is disabled first, and `pm_runtime_barrier`
> +        // waits for pending runtime PM work/callbacks before the callback data
> +        // is removed below.
> +
> +        unsafe {
> +            bindings::__pm_runtime_disable(self.ctx.inner.dev.as_raw(), true);

Same here, is this safe to call even if it's not enabled? Registration can drop
even when pm runtime is not enabled, right?

> +            bindings::pm_runtime_barrier(self.ctx.inner.dev.as_raw());
> +        }

You should not combine multiple unsafe calls in single unsafe block I think.

> +        // SAFETY: The pointer, if non-null, was stored by `Registration::new`
> +        // using `Pin<KBox<RegistrationData<T>>>::into_foreign`. Runtime PM has
> +        // been disabled and drained above, so generated callbacks can no longer
> +        // borrow this data. Clearing `rust_private` prevents later lookup, and
> +        // `from_foreign` reconstructs the owning allocation so it is dropped.
> +        unsafe {
> +            let ptr = (*(*self.ctx.inner.dev.as_raw()).p).rust_private;
> +
> +            if !ptr.is_null() {
> +                (*(*self.ctx.inner.dev.as_raw()).p).rust_private = core::ptr::null_mut();
> +                Pin::<KBox<RegistrationData<'_, T>>>::from_foreign(ptr);
> +            }
> +        }
> +    }
> +}
> -- 
> 2.43.0
>