[v4,2/3] PM / DEVFREQ: add example governors

Commit Message

MyungJoo Ham July 15, 2011, 8:11 a.m. UTC

Three CPUFREQ-like governors are provided as examples.

powersave: use the lowest frequency possible. The user (device) should
set the polling_ms as 0 because polling is useless for this governor.

performance: use the highest freqeuncy possible. The user (device)
should set the polling_ms as 0 because polling is useless for this
governor.

simple_ondemand: simplified version of CPUFREQ's ONDEMAND governor.

When a user updates OPP entries (enable/disable/add), OPP framework
automatically notifies DEVFREQ to update operating frequency
accordingly. Thus, DEVFREQ users (device drivers) do not need to update
DEVFREQ manually with OPP entry updates or set polling_ms for powersave
, performance, or any other "static" governors.

Signed-off-by: MyungJoo Ham <[e-mail]>
Signed-off-by: Kyungmin Park <[e-mail]>

---
Changes from v3:
- Bugfixes on simple-ondemand governor (divide by zero / overflow)
- Style fixes
- Give names to governors
---
 drivers/base/power/devfreq.c |   85 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/devfreq.h      |    5 ++
 2 files changed, 90 insertions(+), 0 deletions(-)

Patch

diff --git a/drivers/base/power/devfreq.c b/drivers/base/power/devfreq.c
index aba9768..e5a73aa 100644
--- a/drivers/base/power/devfreq.c
+++ b/drivers/base/power/devfreq.c
@@ -395,3 +395,88 @@  static int __init devfreq_init(void)
 	return 0;
 }
 late_initcall(devfreq_init);
+
+static int devfreq_powersave_func(struct devfreq *df,
+				  unsigned long *freq)
+{
+	*freq = 0; /* devfreq_do will run "ceiling" to 0 */
+	return 0;
+}
+
+struct devfreq_governor devfreq_powersave = {
+	.name = "powersave",
+	.get_target_freq = devfreq_powersave_func,
+};
+
+static int devfreq_performance_func(struct devfreq *df,
+				    unsigned long *freq)
+{
+	*freq = UINT_MAX; /* devfreq_do will run "floor" */
+	return 0;
+}
+
+struct devfreq_governor devfreq_performance = {
+	.name = "performance",
+	.get_target_freq = devfreq_performance_func,
+};
+
+/* Constants for DevFreq-Simple-Ondemand (DFSO) */
+#define DFSO_UPTHRESHOLD	(90)
+#define DFSO_DOWNDIFFERENCTIAL	(5)
+static int devfreq_simple_ondemand_func(struct devfreq *df,
+					unsigned long *freq)
+{
+	struct devfreq_dev_status stat;
+	int err = df->profile->get_dev_status(df->dev, &stat);
+	unsigned long long a, b;
+
+	if (err)
+		return err;
+
+	/* Assume MAX if it is going to be divided by zero */
+	if (stat.total_time == 0) {
+		*freq = UINT_MAX;
+		return 0;
+	}
+
+	/* Prevent overflow */
+	if (stat.busy_time >= (1 << 24) || stat.total_time >= (1 << 24)) {
+		stat.busy_time >>= 7;
+		stat.total_time >>= 7;
+	}
+
+	/* Set MAX if it's busy enough */
+	if (stat.busy_time * 100 >
+	    stat.total_time * DFSO_UPTHRESHOLD) {
+		*freq = UINT_MAX;
+		return 0;
+	}
+
+	/* Set MAX if we do not know the initial frequency */
+	if (stat.current_frequency == 0) {
+		*freq = UINT_MAX;
+		return 0;
+	}
+
+	/* Keep the current frequency */
+	if (stat.busy_time * 100 >
+	    stat.total_time * (DFSO_UPTHRESHOLD - DFSO_DOWNDIFFERENCTIAL)) {
+		*freq = stat.current_frequency;
+		return 0;
+	}
+
+	/* Set the desired frequency based on the load */
+	a = stat.busy_time;
+	a *= stat.current_frequency;
+	b = div_u64(a, stat.total_time);
+	b *= 100;
+	b = div_u64(b, (DFSO_UPTHRESHOLD - DFSO_DOWNDIFFERENCTIAL / 2));
+	*freq = (unsigned long) b;
+
+	return 0;
+}
+
+struct devfreq_governor devfreq_simple_ondemand = {
+	.name = "simple_ondemand",
+	.get_target_freq = devfreq_simple_ondemand_func,
+};
diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
index 7c881cc..baa074c 100644
--- a/include/linux/devfreq.h
+++ b/include/linux/devfreq.h
@@ -84,6 +84,11 @@  extern int devfreq_add_device(struct device *dev,
 extern int devfreq_remove_device(struct device *dev);
 extern int devfreq_update(struct device *dev);
 extern int devfreq_tickle_device(struct device *dev, unsigned long duration_ms);
+
+extern struct devfreq_governor devfreq_powersave;
+extern struct devfreq_governor devfreq_performance;
+extern struct devfreq_governor devfreq_simple_ondemand;
+
 #else /* !CONFIG_PM_DEVFREQ */
 static int devfreq_add_device(struct device *dev,
 			   struct devfreq_dev_profile *profile,