rp/pio: remove critical section in IrqFuture::poll

there's nothing this critical section protects against. both read and
write-to-clear are atomic and don't interfere with other irq futures,
only potentially with setting/clearing an irq flag from an arm core.
neither have ever been synchronized, and both have the same observable
effects under atomic writes and critical sections. (for both setting and
clearing an irq flag observable differences could only happen if the
set/clear happened after the poll read, but before the write. if it's a
clear we observe the same effects as sequencing the clear entirely after
the poll, and if it's a set we observe the same effects as sequencing
the set entirely before the poll)

1 files changed, 3 insertions, 10 deletions

diff --git a/embassy-rp/src/pio.rs b/embassy-rp/src/pio.rs
index 31273b5d8..c2c144c00 100644
--- a/embassy-rp/src/pio.rs
+++ b/embassy-rp/src/pio.rs
@@ -191,17 +191,10 @@ impl<'a, 'd, PIO: Instance> Future for IrqFuture<'a, 'd, PIO> {
         //debug!("Poll {},{}", PIO::PIO_NO, SM);
 
         // Check if IRQ flag is already set
-        if critical_section::with(|_| unsafe {
-            let irq_flags = PIO::PIO.irq();
-            if irq_flags.read().0 & (1 << self.irq_no) != 0 {
-                irq_flags.write(|m| {
-                    m.0 = 1 << self.irq_no;
-                });
-                true
-            } else {
-                false
+        if unsafe { PIO::PIO.irq().read().0 & (1 << self.irq_no) != 0 } {
+            unsafe {
+                PIO::PIO.irq().write(|m| m.0 = 1 << self.irq_no);
             }
-        }) {
             return Poll::Ready(());
         }