[PATCH] [v4] Add idle wait support for 44x platforms

[PATCH] [v4] Add idle wait support for 44x platforms

[Jerone Young]

2 files changed, 87 insertions(+), 1 deletion(-)
arch/powerpc/platforms/44x/Makefile |    2 
arch/powerpc/platforms/44x/idle.c   |   86 +++++++++++++++++++++++++++++++++++


- adds MSR_DE to MSRs to enable while in wait state

This patch adds the ability for the CPU to go into wait state while in cpu_idle loop. This helps virtulization solutions know when the guest Linux kernel is in an idle state. There are two ways to do it.

1) Command line
	idle=spin <-- CPU will spin (this is the default)
	idle=wait <-- set CPU into wait state when idle

2) The device tree will be checked for the "/hypervisor" node
   If this node is seen it will use "wait" for idle, so that
   the hypervisor can know when guest Linux kernel it is in
   an idle state.

This patch, unlike the last, isolates the code to 44x platforms.

Signed-off-by: Jerone Young <jyoung5@us.ibm.com>

diff --git a/arch/powerpc/platforms/44x/Makefile b/arch/powerpc/platforms/44x/Makefile
--- a/arch/powerpc/platforms/44x/Makefile
+++ b/arch/powerpc/platforms/44x/Makefile
@@ -1,4 +1,4 @@ obj-$(CONFIG_44x)	:= misc_44x.o
-obj-$(CONFIG_44x)	:= misc_44x.o
+obj-$(CONFIG_44x)	:= misc_44x.o idle.o
 obj-$(CONFIG_EBONY)	+= ebony.o
 obj-$(CONFIG_TAISHAN)	+= taishan.o
 obj-$(CONFIG_BAMBOO)	+= bamboo.o
diff --git a/arch/powerpc/platforms/44x/idle.c b/arch/powerpc/platforms/44x/idle.c
new file mode 100644
--- /dev/null
+++ b/arch/powerpc/platforms/44x/idle.c
@@ -0,0 +1,86 @@
+/*
+ * Copyright 2008 IBM Corp. 
+ *
+ * Based on arch/powerpc/platforms/pasemi/idle.c: 
+ * Copyright (C) 2006-2007 PA Semi, Inc
+ *
+ * Added by: Jerone Young <jyoung5@us.ibm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
+ *
+ */
+
+#include <linux/of.h>
+#include <linux/kernel.h>
+#include <asm/machdep.h>
+
+static int current_mode;
+
+struct sleep_mode {
+	char *name;
+	void (*entry)(void);
+};
+
+static void ppc44x_idle(void)
+{
+	unsigned long msr_save;
+
+	msr_save = mfmsr();
+	/* set wait state MSR */
+	mtmsr(msr_save|MSR_WE|MSR_EE|MSR_CE|MSR_DE);
+	isync();
+	/* return to initial state */
+	mtmsr(msr_save);
+	isync();
+}
+
+static struct sleep_mode modes[] = {
+	{ .name = "spin", .entry = NULL },
+	{ .name = "wait", .entry = &ppc44x_idle },
+};
+
+int __init ppc44x_idle_init(void)
+{
+	void *func = modes[current_mode].entry;
+	struct device_node *node;
+
+	node = of_find_node_by_path("/hypervisor");
+	if (node) {
+		/* if we find /hypervisor node is in device tree,
+		   set idle mode to wait */
+		func = &ppc44x_idle; /* wait */
+		of_node_put(node);
+	}
+
+	ppc_md.power_save = func;
+	return 0;
+}
+
+arch_initcall(ppc44x_idle_init);
+
+static int __init idle_param(char *p)
+{ 
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(modes); i++) {
+		if (!strcmp(modes[i].name, p)) {
+			current_mode = i;
+			break;
+		}
+	}
+
+	return 0;
+}
+
+early_param("idle", idle_param);

Re: [PATCH] [v4] Add idle wait support for 44x platforms

[Josh Boyer]

On Fri, 04 Apr 2008 11:28:27 -0500
Jerone Young <jyoung5@us.ibm.com> wrote:

> 2 files changed, 87 insertions(+), 1 deletion(-)
> arch/powerpc/platforms/44x/Makefile |    2 
> arch/powerpc/platforms/44x/idle.c   |   86 +++++++++++++++++++++++++++++++++++
> 
> 
> - adds MSR_DE to MSRs to enable while in wait state
> 
> This patch adds the ability for the CPU to go into wait state while in cpu_idle loop. This helps virtulization solutions know when the guest Linux kernel is in an idle state. There are two ways to do it.
> 
> 1) Command line
> 	idle=spin <-- CPU will spin (this is the default)
> 	idle=wait <-- set CPU into wait state when idle
> 
> 2) The device tree will be checked for the "/hypervisor" node
>    If this node is seen it will use "wait" for idle, so that
>    the hypervisor can know when guest Linux kernel it is in
>    an idle state.
> 
> This patch, unlike the last, isolates the code to 44x platforms.
> 
> Signed-off-by: Jerone Young <jyoung5@us.ibm.com>

This one looks great to me.  Thanks for being persistent.

I'll keep it queued up until early next week.  I've emailed the CPU
engineers to see what exactly wait state does to the core and if they
know of any issues with it.

If it comes back clean from them and we get good test results with it
enabled, then we can likely reverse the default to use it and remove
the check for the hypervisor node.

josh