Subject: powerpc: cpu_idle implementation for systemsim

The original cpu_idle hack from the systemsim git
tree is a bit strange, because it unconditionally
changes the native_idle function. This one instead
introduces a new idle implementation that is only
used on systemsim.

Signed-off-by: Arnd Bergmann <arndb@de.ibm.com>

Index: linus-2.6/arch/powerpc/Kconfig
===================================================================
--- linus-2.6.orig/arch/powerpc/Kconfig
+++ linus-2.6/arch/powerpc/Kconfig
@@ -375,6 +375,15 @@ config PPC_SYSTEMSIM
 	  The Full system simulator is available for download from
 	  http://www.alphaworks.ibm.com/tech/.
 
+config SYSTEMSIM_IDLE
+	bool "   Optimized idle loop for systemsim"
+	depends on PPC_SYSTEMSIM
+	help
+	  Selecting this option will enable an more optimized idle loop
+	  for running on the IBM Full System Simulator that
+	  significantly reduces the load on the host system when
+	  simulating an idle system.
+
 config XICS
 	depends on PPC_PSERIES
 	bool
Index: linus-2.6/arch/powerpc/kernel/setup_64.c
===================================================================
--- linus-2.6.orig/arch/powerpc/kernel/setup_64.c
+++ linus-2.6/arch/powerpc/kernel/setup_64.c
@@ -557,6 +557,23 @@ static void __init emergency_stack_init(
 }
 
 /*
+ * Detect if we are running on top of the IBM Full System Simulator.
+ * If we are, use the optimized idle loop for that case.
+ */
+static void __init setup_systemsim_idle(void)
+{
+#ifdef CONFIG_SYSTEMSIM_IDLE
+	struct device_node *mambo_node;
+
+	mambo_node = of_find_node_by_path("/mambo");
+	if (mambo_node) {
+		ppc_md.idle_loop = systemsim_idle;
+		of_node_put(mambo_node);
+	}
+#endif
+}
+
+/*
  * Called into from start_kernel, after lock_kernel has been called.
  * Initializes bootmem, which is unsed to manage page allocation until
  * mem_init is called.
@@ -603,6 +620,8 @@ void __init setup_arch(char **cmdline_p)
 
 	ppc_md.setup_arch();
 
+	setup_systemsim_idle();
+
 	/* Use the default idle loop if the platform hasn't provided one. */
 	if (NULL == ppc_md.idle_loop) {
 		ppc_md.idle_loop = default_idle;
Index: linus-2.6/include/asm-powerpc/machdep.h
===================================================================
--- linus-2.6.orig/include/asm-powerpc/machdep.h
+++ linus-2.6/include/asm-powerpc/machdep.h
@@ -244,6 +244,7 @@ struct machdep_calls {
 
 extern void default_idle(void);
 extern void native_idle(void);
+extern void systemsim_idle(void);
 
 extern struct machdep_calls ppc_md;
 extern char cmd_line[COMMAND_LINE_SIZE];
Index: linus-2.6/arch/powerpc/kernel/idle_systemsim.c
===================================================================
--- /dev/null
+++ linus-2.6/arch/powerpc/kernel/idle_systemsim.c
@@ -0,0 +1,35 @@
+/*
+ * Idle daemon for the IBM Full System Simulator.
+ *
+ * Originally Written by Cort Dougan (cort@cs.nmt.edu)
+ *    Copyright (c) 2003-2006 IBM Corporation
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/sched.h>
+#include <linux/preempt.h>
+
+#include <asm/systemsim.h>
+
+#define SIM_HALT_CODE 126
+
+static inline void systemsim_halt(void)
+{
+	callthru0(SIM_HALT_CODE);
+}
+
+void systemsim_idle(void)
+{
+	while (1) {
+		while (!need_resched())
+			systemsim_halt();
+
+		preempt_enable_no_resched();
+		schedule();
+		preempt_disable();
+	}
+}
Index: linus-2.6/arch/powerpc/kernel/Makefile
===================================================================
--- linus-2.6.orig/arch/powerpc/kernel/Makefile
+++ linus-2.6/arch/powerpc/kernel/Makefile
@@ -21,6 +21,7 @@ obj-$(CONFIG_PPC64)		+= setup_64.o binfm
 obj-$(CONFIG_PPC64)		+= vdso64/
 obj-$(CONFIG_ALTIVEC)		+= vecemu.o vector.o
 obj-$(CONFIG_POWER4)		+= idle_power4.o
+obj-$(CONFIG_SYSTEMSIM_IDLE)	+= idle_systemsim.o
 obj-$(CONFIG_PPC_OF)		+= of_device.o prom_parse.o
 procfs-$(CONFIG_PPC64)		:= proc_ppc64.o
 obj-$(CONFIG_PROC_FS)		+= $(procfs-y)