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Subject[RFC][PATCH 5/5] PM / Domains: Add default power off governor function
Date
From: Rafael J. Wysocki <rjw@sisk.pl>

Add a function deciding whether or not a given PM domain should
be powered off on the basis of that domain's devices' PM QoS
constraints.

---
drivers/base/power/domain_governor.c | 96 +++++++++++++++++++++++++++++++++++
include/linux/pm_domain.h | 7 ++
2 files changed, 103 insertions(+)

Index: linux/include/linux/pm_domain.h
===================================================================
--- linux.orig/include/linux/pm_domain.h
+++ linux/include/linux/pm_domain.h
@@ -49,6 +49,10 @@ struct generic_pm_domain {
int (*start_device)(struct device *dev);
int (*stop_device)(struct device *dev);
bool (*active_wakeup)(struct device *dev);
+ ktime_t power_off_latency;
+ ktime_t power_on_latency;
+ s64 break_even_ns;
+ s64 min_delta_ns;
};

static inline struct generic_pm_domain *pd_to_genpd(struct dev_pm_domain *pd)
@@ -64,6 +68,9 @@ struct gpd_link {
};

struct gpd_gov_dev_data {
+ ktime_t start_latency;
+ ktime_t suspend_latency;
+ ktime_t resume_latency;
s64 break_even_ns;
};

Index: linux/drivers/base/power/domain_governor.c
===================================================================
--- linux.orig/drivers/base/power/domain_governor.c
+++ linux/drivers/base/power/domain_governor.c
@@ -35,6 +35,102 @@ static bool default_stop_ok(struct devic
return constraint_ns > gov_data->break_even_ns;
}

+/* This routine must be executed under the PM domain's lock. */
+static bool default_power_down_ok(struct dev_pm_domain *pd)
+{
+ struct generic_pm_domain *genpd = pd_to_genpd(pd);
+ struct gpd_link *link;
+ struct pm_domain_data *pdd;
+ ktime_t off_time, on_time;
+ s64 delta_ns, min_delta_ns;
+
+ on_time = genpd->power_on_latency;
+ /* Check if slave domains can be off for enough time. */
+ delta_ns = ktime_to_ns(ktime_add(genpd->power_off_latency, on_time));
+ min_delta_ns = 0;
+ /* All slave domains have been powered off at this point. */
+ list_for_each_entry(link, &genpd->master_links, master_node) {
+ if (delta_ns > link->slave->min_delta_ns)
+ return false;
+
+ delta_ns = link->slave->min_delta_ns - delta_ns;
+ if (delta_ns < min_delta_ns)
+ min_delta_ns = delta_ns;
+ }
+
+ genpd->min_delta_ns = min_delta_ns;
+
+ /* Compute the total time needed to power off the domain. */
+ off_time = ktime_set(0, 0);
+ /* All devices have been stopped at this point. */
+ list_for_each_entry(pdd, &genpd->dev_list, list_node) {
+ struct gpd_gov_dev_data *gov_data;
+
+ if (!pdd->dev->driver)
+ continue;
+
+ gov_data = to_gpd_data(pdd)->gov_data;
+ if (!gov_data)
+ continue;
+
+ off_time = ktime_add(off_time, gov_data->suspend_latency);
+ }
+ off_time = ktime_add(off_time, genpd->power_off_latency);
+
+ /*
+ * For each device in the domain compute the difference between the
+ * QoS value and the total time required to bring the device back
+ * assuming that the domain will be powered off and compute the minimum
+ * of those.
+ */
+ min_delta_ns = 0;
+ on_time = ktime_add(on_time, off_time);
+ list_for_each_entry(pdd, &genpd->dev_list, list_node) {
+ struct gpd_gov_dev_data *gov_data;
+ struct device *dev = pdd->dev;
+ ktime_t dev_up_time;
+ s32 constraint;
+ s64 constraint_ns;
+
+ if (!dev->driver)
+ continue;
+
+ gov_data = to_gpd_data(pdd)->gov_data;
+ if (gov_data) {
+ dev_up_time = ktime_add(on_time,
+ gov_data->resume_latency);
+ dev_up_time = ktime_add(dev_up_time,
+ gov_data->start_latency);
+ } else {
+ dev_up_time = on_time;
+ }
+
+ constraint = dev_pm_qos_read_value(dev);
+ if (constraint < 0)
+ return false;
+ else if (constraint == 0) /* 0 means "don't care" */
+ continue;
+
+ constraint_ns = constraint;
+ constraint_ns *= NSEC_PER_USEC;
+ delta_ns = constraint_ns - ktime_to_ns(dev_up_time);
+ if (min_delta_ns > delta_ns)
+ min_delta_ns = delta_ns;
+ }
+
+ /* Compare the computed delta with the break even value. */
+ if (min_delta_ns < genpd->break_even_ns)
+ return false;
+
+ /* Store the computed value for the masters to use. */
+ if (genpd->min_delta_ns > min_delta_ns)
+ genpd->min_delta_ns = min_delta_ns;
+
+ /* The domain can be powered off. */
+ return true;
+}
+
struct dev_power_governor default_qos_governor = {
.stop_ok = default_stop_ok,
+ .power_down_ok = default_power_down_ok,
};


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