zephyr: device: Use AtomicBool instead of AtomicUsize

Change the AtomicUsize to an AtomicBool to clarify the use.  The flag is
still stored inverted, so false is the correct initializer, and we will
still initialize from zero-initted memory.

Signed-off-by: David Brown <[email protected]>

Author: d3zd3z

zephyr/src/device.rs

@@ -5,7 +5,7 @@
 //!
 //! Most of these instances come from the device tree.
 
-use crate::sync::atomic::{AtomicUsize, Ordering};
+use crate::sync::atomic::{AtomicBool, Ordering};
 
 pub mod gpio;
 pub mod flash;
@@ -21,12 +21,14 @@ pub mod flash;
 /// driver will be shared among then.  Generally, the constructor for the individual device will
 /// call `get_instance_raw()` on the underlying device.
 #[allow(dead_code)]
-pub(crate) struct Unique(pub(crate) AtomicUsize);
+pub(crate) struct Unique(pub(crate) AtomicBool);
 
 impl Unique {
+    // Note that there are circumstances where these are in zero-initialized memory, so false must
+    // be used here, and the result of `once` inverted.
     /// Construct a new unique counter.
     pub(crate) const fn new() -> Unique {
-        Unique(AtomicUsize::new(0))
+        Unique(AtomicBool::new(false))
     }
 
     /// Indicates if this particular entity can be used.  This function, on a given `Unique` value
@@ -35,6 +37,6 @@ impl Unique {
     pub(crate) fn once(&self) -> bool {
         // `fetch_add` is likely to be faster than compare_exchage.  This does have the limitation
         // that `once` is not called more than `usize::MAX` times.
-        self.0.fetch_add(1, Ordering::AcqRel) == 0
+        !self.0.fetch_or(true, Ordering::AcqRel)
     }
 }