fix(rp2350): add software spinlocks

src/runtime/runtime_rp2.go

@@ -297,31 +297,6 @@ var (
 	futexLock     = spinLock{id: 3}
 )
 
-// A hardware spinlock, one of the 32 spinlocks defined in the SIO peripheral.
-type spinLock struct {
-	id uint8
-}
-
-// Return the spinlock register: rp.SIO.SPINLOCKx
-func (l *spinLock) spinlock() *volatile.Register32 {
-	return (*volatile.Register32)(unsafe.Add(unsafe.Pointer(&rp.SIO.SPINLOCK0), l.id*4))
-}
-
-func (l *spinLock) Lock() {
-	// Wait for the lock to be available.
-	spinlock := l.spinlock()
-	for spinlock.Get() == 0 {
-		// TODO: use wfe and send an event when unlocking so the CPU can go to
-		// sleep while waiting for the lock.
-		// Unfortunately when doing that, time.Sleep() seems to hang somewhere.
-		// This needs some debugging to figure out.
-	}
-}
-
-func (l *spinLock) Unlock() {
-	l.spinlock().Set(0)
-}
-
 // Wait until a signal is received, indicating that it can resume from the
 // spinloop.
 func spinLoopWait() {

src/runtime/runtime_rp2040.go

@@ -4,9 +4,36 @@ package runtime
 
 import (
 	"device/rp"
+	"runtime/volatile"
+	"unsafe"
 )
 
 const (
 	sioIrqFifoProc0 = rp.IRQ_SIO_IRQ_PROC0
 	sioIrqFifoProc1 = rp.IRQ_SIO_IRQ_PROC1
 )
+
+// A hardware spinlock, one of the 32 spinlocks defined in the SIO peripheral.
+type spinLock struct {
+	id uint8
+}
+
+// Return the spinlock register: rp.SIO.SPINLOCKx
+func (l *spinLock) spinlock() *volatile.Register32 {
+	return (*volatile.Register32)(unsafe.Add(unsafe.Pointer(&rp.SIO.SPINLOCK0), l.id*4))
+}
+
+func (l *spinLock) Lock() {
+	// Wait for the lock to be available.
+	spinlock := l.spinlock()
+	for spinlock.Get() == 0 {
+		// TODO: use wfe and send an event when unlocking so the CPU can go to
+		// sleep while waiting for the lock.
+		// Unfortunately when doing that, time.Sleep() seems to hang somewhere.
+		// This needs some debugging to figure out.
+	}
+}
+
+func (l *spinLock) Unlock() {
+	l.spinlock().Set(0)
+}

src/runtime/runtime_rp2350.go

@@ -4,6 +4,7 @@ package runtime
 
 import (
 	"device/rp"
+	"sync/atomic"
 )
 
 const (
@@ -14,3 +15,25 @@ const (
 	sioIrqFifoProc0 = rp.IRQ_SIO_IRQ_FIFO
 	sioIrqFifoProc1 = rp.IRQ_SIO_IRQ_FIFO
 )
+
+type spinLock struct {
+	atomic.Uint32
+	id uint8
+}
+
+func (l *spinLock) Lock() {
+	// Try to replace 0 with 1. Once we succeed, the lock has been acquired.
+	for !l.Uint32.CompareAndSwap(0, 1) {
+		spinLoopWait()
+	}
+}
+
+func (l *spinLock) Unlock() {
+	// Safety check: the spinlock should have been locked.
+	if schedulerAsserts && l.Uint32.Load() != 1 {
+		runtimePanic("unlock of unlocked spinlock")
+	}
+
+	// Unlock the lock. Simply write 0, because we already know it is locked.
+	l.Uint32.Store(0)
+}