rp/gpio: add optional pins

embassy-rp/src/gpio.rs

@@ -223,9 +223,11 @@ pub(crate) mod sealed {
             SIO.gpio_in(self.bank() as _)
         }
     }
+
+    pub trait OptionalPin {}
 }
 
-pub trait Pin: sealed::Pin {
+pub trait Pin: Unborrow<Target = Self> + sealed::Pin {
     /// Degrade to a generic pin struct
     fn degrade(self) -> AnyPin {
         AnyPin {
@@ -245,6 +247,56 @@ impl sealed::Pin for AnyPin {
     }
 }
 
+// ==========================
+
+pub trait OptionalPin: Unborrow<Target = Self> + sealed::OptionalPin + Sized {
+    type Pin: Pin;
+    fn pin(&self) -> Option<&Self::Pin>;
+    fn pin_mut(&mut self) -> Option<&mut Self::Pin>;
+
+    /// Convert from concrete pin type PIN_XX to type erased `Option<AnyPin>`.
+    #[inline]
+    fn degrade_optional(mut self) -> Option<AnyPin> {
+        self.pin_mut()
+            .map(|pin| unsafe { core::ptr::read(pin) }.degrade())
+    }
+}
+
+impl<T: Pin> sealed::OptionalPin for T {}
+impl<T: Pin> OptionalPin for T {
+    type Pin = T;
+
+    #[inline]
+    fn pin(&self) -> Option<&T> {
+        Some(self)
+    }
+
+    #[inline]
+    fn pin_mut(&mut self) -> Option<&mut T> {
+        Some(self)
+    }
+}
+
+#[derive(Clone, Copy, Debug)]
+pub struct NoPin;
+unsafe_impl_unborrow!(NoPin);
+impl sealed::OptionalPin for NoPin {}
+impl OptionalPin for NoPin {
+    type Pin = AnyPin;
+
+    #[inline]
+    fn pin(&self) -> Option<&AnyPin> {
+        None
+    }
+
+    #[inline]
+    fn pin_mut(&mut self) -> Option<&mut AnyPin> {
+        None
+    }
+}
+
+// ==========================
+
 macro_rules! impl_pin {
     ($name:ident, $bank:expr, $pin_num:expr) => {
         impl Pin for peripherals::$name {}