Index: arch/m68k/include/lock.h
===================================================================
RCS file: /cvsroot/src/sys/arch/m68k/include/lock.h,v
retrieving revision 1.17
diff -u -p -r1.17 lock.h
--- arch/m68k/include/lock.h	13 Feb 2022 13:41:44 -0000	1.17
+++ arch/m68k/include/lock.h	14 Dec 2025 23:05:42 -0000
@@ -68,21 +68,63 @@ __cpu_simple_lock_set(__cpu_simple_lock_
 	*__ptr = __SIMPLELOCK_LOCKED;
 }
 
+#ifdef __HAVE_M68K_BROKEN_RMC
+#include <sys/atomic.h>
+
+union __cpu_simple_lock_un {
+	unsigned int __cslu_lw;
+	unsigned char __cslu_bytes[4];
+};
+
+#define	__cslu_addr(v)			\
+	(unsigned int *)((vaddr_t)(v) & ~3U)
+#define	__cslu_idx(v)			\
+	(int)((vaddr_t)(v) - ((vaddr_t)(v) & ~3U))
+
+__CTASSERT(sizeof(__cpu_simple_lock_t) == 1);
+#endif /* __HAVE_M68K_BROKEN_RMC */
+
 static __inline void
 __cpu_simple_lock(__cpu_simple_lock_t *alp)
 {
-
+#ifdef __HAVE_M68K_BROKEN_RMC
+	unsigned int *__addr = __cslu_addr(alp);
+	int __idx = __cslu_idx(alp);
+	union __cpu_simple_lock_un __old, __new;
+
+	for (;;) {
+		__old.__cslu_lw = __new.__cslu_lw = atomic_load_relaxed(__addr);
+		__old.__cslu_bytes[__idx] = __SIMPLELOCK_UNLOCKED;
+		__new.__cslu_bytes[__idx] = __SIMPLELOCK_LOCKED;
+		if (atomic_cas_uint(__addr, __old.__cslu_lw,
+				    __new.__cslu_lw) == __old.__cslu_lw) {
+			return;
+		}
+	}
+#else
 	__asm volatile(
 		"1:	tas	%0	\n"
 		"	jne	1b	\n"
 		: "=m" (*alp)
 		: /* no inputs */
 		: "cc", "memory");
+#endif /* __HAVE_M68K_BROKEN_RMC */
 }
 
 static __inline int
 __cpu_simple_lock_try(__cpu_simple_lock_t *alp)
 {
+#ifdef __HAVE_M68K_BROKEN_RMC
+	unsigned int *__addr = __cslu_addr(alp);
+	int __idx = __cslu_idx(alp);
+	union __cpu_simple_lock_un __old, __new;
+
+	__old.__cslu_lw = __new.__cslu_lw = atomic_load_relaxed(__addr);
+	__old.__cslu_bytes[__idx] = __SIMPLELOCK_UNLOCKED;
+	__new.__cslu_bytes[__idx] = __SIMPLELOCK_LOCKED;
+	return atomic_cas_uint(__addr, __old.__cslu_lw,
+			       __new.__cslu_lw) == __old.__cslu_lw;
+#else
 	int __rv;
 
 	__asm volatile(
@@ -96,6 +138,7 @@ __cpu_simple_lock_try(__cpu_simple_lock_
 		: "cc", "memory");
 
 	return (__rv);
+#endif /* __HAVE_M68K_BROKEN_RMC */
 }
 
 static __inline void