Optimize PeripheralMutex code size

embassy-nrf/src/util/peripheral.rs

@@ -1,9 +1,11 @@
+use core::array::IntoIter;
 use core::cell::UnsafeCell;
 use core::marker::{PhantomData, PhantomPinned};
+use core::mem::MaybeUninit;
 use core::pin::Pin;
 use core::sync::atomic::{compiler_fence, Ordering};
 
-use crate::fmt::*;
+use crate::fmt::{assert, *};
 use crate::interrupt::Interrupt;
 
 pub trait PeripheralState {
@@ -11,8 +13,19 @@ pub trait PeripheralState {
     fn on_interrupt(&mut self);
 }
 
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+enum Life {
+    Ready,
+    Created,
+    Freed,
+}
+
 pub struct PeripheralMutex<S: PeripheralState> {
-    inner: Option<(UnsafeCell<S>, S::Interrupt)>,
+    life: Life,
+
+    state: MaybeUninit<UnsafeCell<S>>, // Init if life != Freed
+    irq: MaybeUninit<S::Interrupt>,    // Init if life != Freed
+
     _not_send: PhantomData<*mut ()>,
     _pinned: PhantomPinned,
 }
@@ -20,16 +33,19 @@ pub struct PeripheralMutex<S: PeripheralState> {
 impl<S: PeripheralState> PeripheralMutex<S> {
     pub fn new(state: S, irq: S::Interrupt) -> Self {
         Self {
-            inner: Some((UnsafeCell::new(state), irq)),
+            life: Life::Created,
+            state: MaybeUninit::new(UnsafeCell::new(state)),
+            irq: MaybeUninit::new(irq),
             _not_send: PhantomData,
             _pinned: PhantomPinned,
         }
     }
 
-    pub fn with<R>(self: Pin<&mut Self>, f: impl FnOnce(&mut S, &mut S::Interrupt) -> R) -> R {
-        let this = unsafe { self.get_unchecked_mut() };
-        let (state, irq) = unwrap!(this.inner.as_mut());
+    /// safety: self must be pinned.
+    unsafe fn setup(&mut self) {
+        assert!(self.life == Life::Created);
 
+        let irq = &mut *self.irq.as_mut_ptr();
         irq.disable();
         compiler_fence(Ordering::SeqCst);
 
@@ -37,13 +53,30 @@ impl<S: PeripheralState> PeripheralMutex<S> {
             // Safety: it's OK to get a &mut to the state, since
             // - We're in the IRQ, no one else can't preempt us
             // - We can't have preempted a with() call because the irq is disabled during it.
-            let state = unsafe { &mut *(p as *mut S) };
+            let state = &mut *(p as *mut S);
             state.on_interrupt();
         });
-        irq.set_handler_context(state.get() as *mut ());
+        irq.set_handler_context(self.state.as_mut_ptr() as *mut ());
+
+        compiler_fence(Ordering::SeqCst);
+        irq.enable();
+
+        self.life = Life::Ready;
+    }
+
+    pub fn with<R>(self: Pin<&mut Self>, f: impl FnOnce(&mut S, &mut S::Interrupt) -> R) -> R {
+        let this = unsafe { self.get_unchecked_mut() };
+        if this.life != Life::Ready {
+            unsafe { this.setup() }
+        }
+
+        let irq = unsafe { &mut *this.irq.as_mut_ptr() };
+
+        irq.disable();
+        compiler_fence(Ordering::SeqCst);
 
         // Safety: it's OK to get a &mut to the state, since the irq is disabled.
-        let state = unsafe { &mut *state.get() };
+        let state = unsafe { &mut *(*this.state.as_ptr()).get() };
 
         let r = f(state, irq);
 
@@ -55,11 +88,19 @@ impl<S: PeripheralState> PeripheralMutex<S> {
 
     pub fn try_free(self: Pin<&mut Self>) -> Option<(S, S::Interrupt)> {
         let this = unsafe { self.get_unchecked_mut() };
-        this.inner.take().map(|(state, irq)| {
-            irq.disable();
-            irq.remove_handler();
-            (state.into_inner(), irq)
-        })
+
+        if this.life != Life::Freed {
+            return None;
+        }
+
+        unsafe { &mut *this.irq.as_mut_ptr() }.disable();
+        compiler_fence(Ordering::SeqCst);
+
+        this.life = Life::Freed;
+
+        let state = unsafe { this.state.as_ptr().read().into_inner() };
+        let irq = unsafe { this.irq.as_ptr().read() };
+        Some((state, irq))
     }
 
     pub fn free(self: Pin<&mut Self>) -> (S, S::Interrupt) {
@@ -69,7 +110,8 @@ impl<S: PeripheralState> PeripheralMutex<S> {
 
 impl<S: PeripheralState> Drop for PeripheralMutex<S> {
     fn drop(&mut self) {
-        if let Some((_state, irq)) = &mut self.inner {
+        if self.life != Life::Freed {
+            let irq = unsafe { &mut *self.irq.as_mut_ptr() };
             irq.disable();
             irq.remove_handler();
         }