linux-kernel - [PATCH] cpufreq: powernv: Export frequency throttle state of the chip through sysfs

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Date:	Thu, 27 Aug 2015 14:43:26 +0530
From:	Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
To:	rjw@...ysocki.net
Cc:	stewart@...ux.vnet.ibm.com, viresh.kumar@...aro.org,
	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org,
	Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
Subject: [PATCH] cpufreq: powernv: Export frequency throttle state of the chip through sysfs

Create a sysfs 'throttle' attribute per-chip(per-numa-node) to reflect
the throttle state of the chip. The usersapce programs can poll on
this attribute to keep an eye on the throttle state. Currently we
print a log message to notify the user of throttling event. The
performance-sensitive applications can monitor the throttle state
using this attribute.

Following file is created in sysfs:
/sys/devices/system/node/nodeN/throttle
'throttle' attribute has the following values:
0 : frequency is unthrottled
1 : frequency is throttled

Suggested-by: Stewart Smith <stewart@...ux.vnet.ibm.com>
Signed-off-by: Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
---
This patch is based on top of linux-next/master 

 drivers/cpufreq/powernv-cpufreq.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
index 64994e1..aed6c34 100644
--- a/drivers/cpufreq/powernv-cpufreq.c
+++ b/drivers/cpufreq/powernv-cpufreq.c
@@ -28,6 +28,8 @@
 #include <linux/of.h>
 #include <linux/reboot.h>
 #include <linux/slab.h>
+#include <linux/device.h>
+#include <linux/node.h>
 
 #include <asm/cputhreads.h>
 #include <asm/firmware.h>
@@ -413,6 +415,23 @@ static struct notifier_block powernv_cpufreq_reboot_nb = {
 	.notifier_call = powernv_cpufreq_reboot_notifier,
 };
 
+static ssize_t throttle_show(struct device *dev,
+			     struct device_attribute *attr, char *buf)
+{
+	int i;
+
+	for (i = 0; i < nr_chips; i++)
+		if (chips[i].id == dev->id) {
+			smp_call_function_any(&chips[i].mask,
+					      powernv_cpufreq_throttle_check,
+					      NULL, 1);
+			return sprintf(buf, "%d\n", throttled ||
+						    chips[i].throttled);
+		}
+}
+
+static DEVICE_ATTR(throttle, 0400, throttle_show, NULL);
+
 void powernv_cpufreq_work_fn(struct work_struct *work)
 {
 	struct chip *chip = container_of(work, struct chip, throttle);
@@ -570,6 +589,8 @@ static int init_chip_info(void)
 		cpumask_copy(&chips[i].mask, cpumask_of_node(chip[i]));
 		INIT_WORK(&chips[i].throttle, powernv_cpufreq_work_fn);
 		chips[i].restore = false;
+		device_create_file(&node_devices[chip[i]]->dev,
+				   &dev_attr_throttle);
 	}
 
 	return 0;
-- 
1.9.3

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