simplify PinGuard and reduce its size

PinGuard's sole purpose is to disconnect the pin when it is dropped. The
only thing really required to do so is the contained pin number. The
signal that it is connected to was in fact never used, but stored in the
struct anyway. This changes PinGuard to only store the pin number, with
pin number 0xFF still indicating an unconnected PinGuard.

Previously, the size of PinGuard was 2 or 4, depending on device.
With this change, PinGuard takes 1 or 2 bytes.
In each case, Option<PinGuard> and PinGuard have identical size due to
taking advantage of niches in the OutputSignal enum.

Additionally, this replaces all uses of Option<PinGuard> by plain
PinGuard: From my understanding, there was no meaningful difference
between Option<PinGuard> and PinGuard::new_unconnected() (both implying
that nothing should happen on Drop).

One consequence is that PinGuard::new_unconnected() can now be
constructed without being able to name an output signal. This will be
useful for the RMT driver, which uses the same Channel struct for rx and
tx configuration (Channel does not presently contain a PinGuard, but
arguably, it should).

Author: wisp3rwind

esp-hal/src/gpio/interconnect.rs

@@ -393,10 +393,10 @@ impl Signal<'_> {
         }
     }
 
-    fn connect_with_guard(self, signal: crate::gpio::OutputSignal) -> PinGuard {
+    fn into_guard(self) -> PinGuard {
         match self {
-            Signal::Pin(pin) => PinGuard::new(pin, signal),
-            Signal::Level(_) => PinGuard::new_unconnected(signal),
+            Signal::Pin(pin) => PinGuard::new(pin),
+            Signal::Level(_) => PinGuard::new_unconnected(),
         }
     }
 
@@ -864,7 +864,7 @@ impl<'d> OutputSignal<'d> {
     #[instability::unstable]
     pub(crate) fn connect_with_guard(self, signal: crate::gpio::OutputSignal) -> PinGuard {
         signal.connect_to(&self);
-        self.pin.connect_with_guard(signal)
+        self.pin.into_guard()
     }
 
     delegate::delegate! {

esp-hal/src/gpio/mod.rs

@@ -64,6 +64,7 @@ crate::unstable_module! {
     #[cfg(all(soc_has_rtc_io, not(esp32)))]
     pub mod rtc_io;
 }
+use interconnect::PeripheralOutput;
 
 mod asynch;
 mod embedded_hal_impls;
@@ -99,24 +100,17 @@ pub(crate) static GPIO_LOCK: RawMutex = RawMutex::new();
 #[cfg_attr(feature = "defmt", derive(defmt::Format))]
 pub(crate) struct PinGuard {
     pin: u8,
-    signal: OutputSignal,
 }
 
 impl crate::private::Sealed for PinGuard {}
 
 impl PinGuard {
-    pub(crate) fn new(pin: AnyPin<'_>, signal: OutputSignal) -> Self {
-        Self {
-            pin: pin.number(),
-            signal,
-        }
+    pub(crate) fn new(pin: AnyPin<'_>) -> Self {
+        Self { pin: pin.number() }
     }
 
-    pub(crate) fn new_unconnected(signal: OutputSignal) -> Self {
-        Self {
-            pin: u8::MAX,
-            signal,
-        }
+    pub(crate) fn new_unconnected() -> Self {
+        Self { pin: u8::MAX }
     }
 
     #[allow(unused)]
@@ -133,7 +127,7 @@ impl Drop for PinGuard {
     fn drop(&mut self) {
         if self.pin != u8::MAX {
             let pin = unsafe { AnyPin::steal(self.pin) };
-            self.signal.disconnect_from(&pin);
+            pin.disconnect_from_peripheral_output();
         }
     }
 }

esp-hal/src/i2c/master/mod.rs

@@ -715,8 +715,8 @@ impl<'d> I2c<'d, Blocking> {
     pub fn new(i2c: impl Instance + 'd, config: Config) -> Result<Self, ConfigError> {
         let guard = PeripheralGuard::new(i2c.info().peripheral);
 
-        let sda_pin = PinGuard::new_unconnected(i2c.info().sda_output);
-        let scl_pin = PinGuard::new_unconnected(i2c.info().scl_output);
+        let sda_pin = PinGuard::new_unconnected();
+        let scl_pin = PinGuard::new_unconnected();
 
         let mut i2c = I2c {
             i2c: i2c.degrade(),

esp-hal/src/spi/master.rs

@@ -616,16 +616,16 @@ struct SpiPinGuard {
     cs_pin: PinGuard,
     sio0_pin: PinGuard,
     sio1_pin: PinGuard,
-    sio2_pin: Option<PinGuard>,
-    sio3_pin: Option<PinGuard>,
+    sio2_pin: PinGuard,
+    sio3_pin: PinGuard,
     #[cfg(spi_master_has_octal)]
-    sio4_pin: Option<PinGuard>,
+    sio4_pin: PinGuard,
     #[cfg(spi_master_has_octal)]
-    sio5_pin: Option<PinGuard>,
+    sio5_pin: PinGuard,
     #[cfg(spi_master_has_octal)]
-    sio6_pin: Option<PinGuard>,
+    sio6_pin: PinGuard,
     #[cfg(spi_master_has_octal)]
-    sio7_pin: Option<PinGuard>,
+    sio7_pin: PinGuard,
 }
 
 /// Configuration errors.
@@ -710,20 +710,20 @@ impl<'d> Spi<'d, Blocking> {
             _mode: PhantomData,
             guard,
             pins: SpiPinGuard {
-                sclk_pin: PinGuard::new_unconnected(spi.info().sclk),
-                cs_pin: PinGuard::new_unconnected(spi.info().cs(0)),
-                sio0_pin: PinGuard::new_unconnected(spi.info().sio_output(0)),
-                sio1_pin: PinGuard::new_unconnected(spi.info().sio_output(1)),
-                sio2_pin: spi.info().opt_sio_output(2).map(PinGuard::new_unconnected),
-                sio3_pin: spi.info().opt_sio_output(3).map(PinGuard::new_unconnected),
+                sclk_pin: PinGuard::new_unconnected(),
+                cs_pin: PinGuard::new_unconnected(),
+                sio0_pin: PinGuard::new_unconnected(),
+                sio1_pin: PinGuard::new_unconnected(),
+                sio2_pin: PinGuard::new_unconnected(),
+                sio3_pin: PinGuard::new_unconnected(),
                 #[cfg(spi_master_has_octal)]
-                sio4_pin: spi.info().opt_sio_output(4).map(PinGuard::new_unconnected),
+                sio4_pin: PinGuard::new_unconnected(),
                 #[cfg(spi_master_has_octal)]
-                sio5_pin: spi.info().opt_sio_output(5).map(PinGuard::new_unconnected),
+                sio5_pin: PinGuard::new_unconnected(),
                 #[cfg(spi_master_has_octal)]
-                sio6_pin: spi.info().opt_sio_output(6).map(PinGuard::new_unconnected),
+                sio6_pin: PinGuard::new_unconnected(),
                 #[cfg(spi_master_has_octal)]
-                sio7_pin: spi.info().opt_sio_output(7).map(PinGuard::new_unconnected),
+                sio7_pin: PinGuard::new_unconnected(),
             },
             spi: spi.degrade(),
         };
@@ -922,7 +922,7 @@ macro_rules! def_with_sio_pin {
         #[doc = concat!(" to the SIO", stringify!($n), " output and input signals.")]
         #[instability::unstable]
         pub fn $fn(mut self, sio: impl PeripheralOutput<'d>) -> Self {
-            self.pins.$field = Some(self.connect_sio_pin(sio.into(), $n));
+            self.pins.$field = self.connect_sio_pin(sio.into(), $n);
 
             self
         }

esp-hal/src/uart/mod.rs

@@ -469,8 +469,8 @@ where
 
         let mem_guard = create_mem_guard(unsafe { self.uart.clone_unchecked() });
 
-        let rts_pin = PinGuard::new_unconnected(self.uart.info().rts_signal);
-        let tx_pin = PinGuard::new_unconnected(self.uart.info().tx_signal);
+        let rts_pin = PinGuard::new_unconnected();
+        let tx_pin = PinGuard::new_unconnected();
 
         let mut serial = Uart {
             rx: UartRx {