1 files changed, 42 insertions, 0 deletions
diff --git a/arch/m68k/include/asm/switch_to.h b/arch/m68k/include/asm/switch_to.h
new file mode 100644
index 000000000..94f02f46c
--- /dev/null
+++ b/arch/m68k/include/asm/switch_to.h
@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _M68K_SWITCH_TO_H
+#define _M68K_SWITCH_TO_H
+
+/*
+ * switch_to(n) should switch tasks to task ptr, first checking that
+ * ptr isn't the current task, in which case it does nothing.  This
+ * also clears the TS-flag if the task we switched to has used the
+ * math co-processor latest.
+ */
+/*
+ * switch_to() saves the extra registers, that are not saved
+ * automatically by SAVE_SWITCH_STACK in resume(), ie. d0-d5 and
+ * a0-a1. Some of these are used by schedule() and its predecessors
+ * and so we might get see unexpected behaviors when a task returns
+ * with unexpected register values.
+ *
+ * syscall stores these registers itself and none of them are used
+ * by syscall after the function in the syscall has been called.
+ *
+ * Beware that resume now expects *next to be in d1 and the offset of
+ * tss to be in a1. This saves a few instructions as we no longer have
+ * to push them onto the stack and read them back right after.
+ *
+ * 02/17/96 - Jes Sorensen (jds@kom.auc.dk)
+ *
+ * Changed 96/09/19 by Andreas Schwab
+ * pass prev in a0, next in a1
+ */
+asmlinkage void resume(void);
+#define switch_to(prev,next,last) do { \
+  register void *_prev __asm__ ("a0") = (prev); \
+  register void *_next __asm__ ("a1") = (next); \
+  register void *_last __asm__ ("d1"); \
+  __asm__ __volatile__("jbsr resume" \
+		       : "=a" (_prev), "=a" (_next), "=d" (_last) \
+		       : "0" (_prev), "1" (_next) \
+		       : "d0", "d2", "d3", "d4", "d5"); \
+  (last) = _last; \
+} while (0)
+
+#endif /* _M68K_SWITCH_TO_H */