Merge tag 'pm-6.16-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm

Pull power management fixes from Rafael Wysocki:
 "These fix the cpupower utility installation, fix up the recently added
  Rust abstractions for cpufreq and OPP, restore the x86 update
  eliminating mwait_play_dead_cpuid_hint() that has been reverted during
  the 6.16 merge window along with preventing the failure caused by it
  from happening, and clean up mwait_idle_with_hints() usage in
  intel_idle:

   - Implement CpuId Rust abstraction and use it to fix doctest failure
     related to the recently introduced cpumask abstraction (Viresh
     Kumar)

   - Do minor cleanups in the `# Safety` sections for cpufreq
     abstractions added recently (Viresh Kumar)

   - Unbreak cpupower systemd service units installation on some systems
     by adding a unitdir variable for specifying the location to install
     them (Francesco Poli)

   - Eliminate mwait_play_dead_cpuid_hint() again after reverting its
     elimination during the 6.16 merge window due to a problem with
     handling "dead" SMT siblings, but this time prevent leaving them in
     C1 after initialization by taking them online and back offline when
     a proper cpuidle driver for the platform has been registered
     (Rafael Wysocki)

   - Update data types of variables passed as arguments to
     mwait_idle_with_hints() to match the function definition after
     recent changes (Uros Bizjak)"

* tag 'pm-6.16-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm:
  rust: cpu: Add CpuId::current() to retrieve current CPU ID
  rust: Use CpuId in place of raw CPU numbers
  rust: cpu: Introduce CpuId abstraction
  intel_idle: Update arguments of mwait_idle_with_hints()
  cpufreq: Convert `/// SAFETY` lines to `# Safety` sections
  cpupower: split unitdir from libdir in Makefile
  Reapply "x86/smp: Eliminate mwait_play_dead_cpuid_hint()"
  ACPI: processor: Rescan "dead" SMT siblings during initialization
  intel_idle: Rescan "dead" SMT siblings during initialization
  x86/smp: PM/hibernate: Split arch_resume_nosmt()
  intel_idle: Use subsys_initcall_sync() for initialization

1 files changed, 123 insertions, 2 deletions

diff --git a/rust/kernel/cpu.rs b/rust/kernel/cpu.rs
index 10c5c3b25873..b75403b0eb56 100644
--- a/rust/kernel/cpu.rs
+++ b/rust/kernel/cpu.rs
@@ -6,6 +6,127 @@
 
 use crate::{bindings, device::Device, error::Result, prelude::ENODEV};
 
+/// Returns the maximum number of possible CPUs in the current system configuration.
+#[inline]
+pub fn nr_cpu_ids() -> u32 {
+    #[cfg(any(NR_CPUS_1, CONFIG_FORCE_NR_CPUS))]
+    {
+        bindings::NR_CPUS
+    }
+
+    #[cfg(not(any(NR_CPUS_1, CONFIG_FORCE_NR_CPUS)))]
+    // SAFETY: `nr_cpu_ids` is a valid global provided by the kernel.
+    unsafe {
+        bindings::nr_cpu_ids
+    }
+}
+
+/// The CPU ID.
+///
+/// Represents a CPU identifier as a wrapper around an [`u32`].
+///
+/// # Invariants
+///
+/// The CPU ID lies within the range `[0, nr_cpu_ids())`.
+///
+/// # Examples
+///
+/// ```
+/// use kernel::cpu::CpuId;
+///
+/// let cpu = 0;
+///
+/// // SAFETY: 0 is always a valid CPU number.
+/// let id = unsafe { CpuId::from_u32_unchecked(cpu) };
+///
+/// assert_eq!(id.as_u32(), cpu);
+/// assert!(CpuId::from_i32(0).is_some());
+/// assert!(CpuId::from_i32(-1).is_none());
+/// ```
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub struct CpuId(u32);
+
+impl CpuId {
+    /// Creates a new [`CpuId`] from the given `id` without checking bounds.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that `id` is a valid CPU ID (i.e., `0 <= id < nr_cpu_ids()`).
+    #[inline]
+    pub unsafe fn from_i32_unchecked(id: i32) -> Self {
+        debug_assert!(id >= 0);
+        debug_assert!((id as u32) < nr_cpu_ids());
+
+        // INVARIANT: The function safety guarantees `id` is a valid CPU id.
+        Self(id as u32)
+    }
+
+    /// Creates a new [`CpuId`] from the given `id`, checking that it is valid.
+    pub fn from_i32(id: i32) -> Option<Self> {
+        if id < 0 || id as u32 >= nr_cpu_ids() {
+            None
+        } else {
+            // INVARIANT: `id` has just been checked as a valid CPU ID.
+            Some(Self(id as u32))
+        }
+    }
+
+    /// Creates a new [`CpuId`] from the given `id` without checking bounds.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that `id` is a valid CPU ID (i.e., `0 <= id < nr_cpu_ids()`).
+    #[inline]
+    pub unsafe fn from_u32_unchecked(id: u32) -> Self {
+        debug_assert!(id < nr_cpu_ids());
+
+        // Ensure the `id` fits in an [`i32`] as it's also representable that way.
+        debug_assert!(id <= i32::MAX as u32);
+
+        // INVARIANT: The function safety guarantees `id` is a valid CPU id.
+        Self(id)
+    }
+
+    /// Creates a new [`CpuId`] from the given `id`, checking that it is valid.
+    pub fn from_u32(id: u32) -> Option<Self> {
+        if id >= nr_cpu_ids() {
+            None
+        } else {
+            // INVARIANT: `id` has just been checked as a valid CPU ID.
+            Some(Self(id))
+        }
+    }
+
+    /// Returns CPU number.
+    #[inline]
+    pub fn as_u32(&self) -> u32 {
+        self.0
+    }
+
+    /// Returns the ID of the CPU the code is currently running on.
+    ///
+    /// The returned value is considered unstable because it may change
+    /// unexpectedly due to preemption or CPU migration. It should only be
+    /// used when the context ensures that the task remains on the same CPU
+    /// or the users could use a stale (yet valid) CPU ID.
+    pub fn current() -> Self {
+        // SAFETY: raw_smp_processor_id() always returns a valid CPU ID.
+        unsafe { Self::from_u32_unchecked(bindings::raw_smp_processor_id()) }
+    }
+}
+
+impl From<CpuId> for u32 {
+    fn from(id: CpuId) -> Self {
+        id.as_u32()
+    }
+}
+
+impl From<CpuId> for i32 {
+    fn from(id: CpuId) -> Self {
+        id.as_u32() as i32
+    }
+}
+
 /// Creates a new instance of CPU's device.
 ///
 /// # Safety
@@ -17,9 +138,9 @@ use crate::{bindings, device::Device, error::Result, prelude::ENODEV};
 /// Callers must ensure that the CPU device is not used after it has been unregistered.
 /// This can be achieved, for example, by registering a CPU hotplug notifier and removing
 /// any references to the CPU device within the notifier's callback.
-pub unsafe fn from_cpu(cpu: u32) -> Result<&'static Device> {
+pub unsafe fn from_cpu(cpu: CpuId) -> Result<&'static Device> {
     // SAFETY: It is safe to call `get_cpu_device()` for any CPU.
-    let ptr = unsafe { bindings::get_cpu_device(cpu) };
+    let ptr = unsafe { bindings::get_cpu_device(u32::from(cpu)) };
     if ptr.is_null() {
         return Err(ENODEV);
     }