rp/uart: extract common code from async and blocking buffered reads

once we add error propagation the common code will become even larger,
so it makes sense to move it out.

embassy-rp/src/uart/buffered.rs

@@ -183,8 +183,20 @@ impl<'d, T: Instance> BufferedUartRx<'d, T> {
         Self { phantom: PhantomData }
     }
 
-    fn read<'a>(buf: &'a mut [u8]) -> impl Future<Output = Result<usize, Error>> + 'a {
+    fn read<'a>(buf: &'a mut [u8]) -> impl Future<Output = Result<usize, Error>> + 'a
+    where
+        T: 'd,
+    {
         poll_fn(move |cx| {
+            if let Poll::Ready(r) = Self::try_read(buf) {
+                return Poll::Ready(r);
+            }
+            T::buffered_state().rx_waker.register(cx.waker());
+            Poll::Pending
+        })
+    }
+
+    fn try_read(buf: &mut [u8]) -> Poll<Result<usize, Error>> {
         if buf.is_empty() {
             return Poll::Ready(Ok(0));
         }
@@ -196,10 +208,12 @@ impl<'d, T: Instance> BufferedUartRx<'d, T> {
             buf[..n].copy_from_slice(&data[..n]);
             n
         });
-            if n == 0 {
-                state.rx_waker.register(cx.waker());
+
+        let result = if n == 0 {
             return Poll::Pending;
-            }
+        } else {
+            Ok(n)
+        };
 
         // (Re-)Enable the interrupt to receive more data in case it was
         // disabled because the buffer was full.
@@ -211,36 +225,14 @@ impl<'d, T: Instance> BufferedUartRx<'d, T> {
             });
         }
 
-            Poll::Ready(Ok(n))
-        })
+        Poll::Ready(result)
     }
 
     pub fn blocking_read(&mut self, buf: &mut [u8]) -> Result<usize, Error> {
-        if buf.is_empty() {
-            return Ok(0);
-        }
-
         loop {
-            let state = T::buffered_state();
-            let mut rx_reader = unsafe { state.rx_buf.reader() };
-            let n = rx_reader.pop(|data| {
-                let n = data.len().min(buf.len());
-                buf[..n].copy_from_slice(&data[..n]);
-                n
-            });
-
-            if n > 0 {
-                // (Re-)Enable the interrupt to receive more data in case it was
-                // disabled because the buffer was full.
-                let regs = T::regs();
-                unsafe {
-                    regs.uartimsc().write_set(|w| {
-                        w.set_rxim(true);
-                        w.set_rtim(true);
-                    });
-                }
-
-                return Ok(n);
+            match Self::try_read(buf) {
+                Poll::Ready(res) => return res,
+                Poll::Pending => continue,
             }
         }
     }