From ae907af48b0c82950cf2e153835fab97b31e7869 Mon Sep 17 00:00:00 2001
From: skrll <skrll@NetBSD.org>
Date: Sat, 14 May 2022 06:07:53 +0000
Subject: [PATCH] Add some special NOPs to help qemu.

thanks to Helge Deller for the heads-up.
---
 sys/arch/hppa/hppa/idle_machdep.c |  9 ++++++---
 sys/arch/hppa/hppa/machdep.c      | 13 +++++++++----
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/sys/arch/hppa/hppa/idle_machdep.c b/sys/arch/hppa/hppa/idle_machdep.c
index 636b07d8a384..cd3384b8ebb7 100644
--- a/sys/arch/hppa/hppa/idle_machdep.c
+++ b/sys/arch/hppa/hppa/idle_machdep.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: idle_machdep.c,v 1.3 2019/04/15 20:45:08 skrll Exp $	*/
+/*	$NetBSD: idle_machdep.c,v 1.4 2022/05/14 06:07:53 skrll Exp $	*/
 
 /*
  * Copyright (c) 2002, 2006, 2007 YAMAMOTO Takashi,
@@ -28,7 +28,7 @@
 
 #include <sys/cdefs.h>
 
-__KERNEL_RCSID(0, "$NetBSD: idle_machdep.c,v 1.3 2019/04/15 20:45:08 skrll Exp $");
+__KERNEL_RCSID(0, "$NetBSD: idle_machdep.c,v 1.4 2022/05/14 06:07:53 skrll Exp $");
 
 #include <sys/param.h>
 #include <sys/cpu.h>
@@ -36,5 +36,8 @@ __KERNEL_RCSID(0, "$NetBSD: idle_machdep.c,v 1.3 2019/04/15 20:45:08 skrll Exp $
 void
 cpu_idle(void)
 {
-	/* do nothing */
+        /*
+	 * This NOP instruction is used by qemu to detect the idle loop.
+	 */
+	__asm volatile("or	%%r10,%%r10,%%r10" ::: "memory");
 }
diff --git a/sys/arch/hppa/hppa/machdep.c b/sys/arch/hppa/hppa/machdep.c
index 7b41da38ca07..5b427fd213ca 100644
--- a/sys/arch/hppa/hppa/machdep.c
+++ b/sys/arch/hppa/hppa/machdep.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: machdep.c,v 1.16 2020/09/14 16:11:32 skrll Exp $	*/
+/*	$NetBSD: machdep.c,v 1.17 2022/05/14 06:07:53 skrll Exp $	*/
 
 /*-
  * Copyright (c) 2001, 2002 The NetBSD Foundation, Inc.
@@ -58,7 +58,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: machdep.c,v 1.16 2020/09/14 16:11:32 skrll Exp $");
+__KERNEL_RCSID(0, "$NetBSD: machdep.c,v 1.17 2022/05/14 06:07:53 skrll Exp $");
 
 #include "opt_cputype.h"
 #include "opt_ddb.h"
@@ -1447,8 +1447,13 @@ cpu_reboot(int howto, char *user_boot_string)
 		    :: "r" (CMD_RESET), "r" (HPPA_LBCAST + iomod_command));
 	}
 
-	for (;;)
-		/* loop while bus reset is coming up */ ;
+	for (;;) {
+		/*
+		 * loop while bus reset is coming up.  This NOP instruction
+		 * is used by qemu to detect the 'death loop'.
+		 */
+		__asm volatile("or %%r31, %%r31, %%r31" ::: "memory");
+	}
 	/* NOTREACHED */
 }