PM / Domains: Cache device stop and domain power off governor results, v3

The results of the default device stop and domain power off governor
functions for generic PM domains, default_stop_ok() and
default_power_down_ok(), depend only on the timing data of devices,
which are static, and on their PM QoS constraints.  Thus, in theory,
these functions only need to carry out their computations, which may
be time consuming in general, when it is known that the PM QoS
constraint of at least one of the devices in question has changed.

Use the PM QoS notifiers of devices to implement that.  First,
introduce new fields, constraint_changed and max_off_time_changed,
into struct gpd_timing_data and struct generic_pm_domain,
respectively, and register a PM QoS notifier function when adding
a device into a domain that will set those fields to 'true' whenever
the device's PM QoS constraint is modified.  Second, make
default_stop_ok() and default_power_down_ok() use those fields to
decide whether or not to carry out their computations from scratch.

The device and PM domain hierarchies are taken into account in that
and the expense is that the changes of PM QoS constraints of
suspended devices will not be taken into account immediately, which
isn't guaranteed anyway in general.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

1 files changed, 7 insertions, 0 deletions

diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
index e7ada5ccdfc2..1e994eeacdf3 100644
--- a/include/linux/pm_domain.h
+++ b/include/linux/pm_domain.h
@@ -14,6 +14,7 @@
 #include <linux/pm.h>
 #include <linux/err.h>
 #include <linux/of.h>
+#include <linux/notifier.h>
 
 enum gpd_status {
         GPD_STATE_ACTIVE = 0,   /* PM domain is active */
@@ -71,6 +72,8 @@ struct generic_pm_domain {
         s64 power_on_latency_ns;
         struct gpd_dev_ops dev_ops;
         s64 max_off_time_ns;    /* Maximum allowed "suspended" time. */
+        bool max_off_time_changed;
+        bool cached_power_down_ok;
         struct device_node *of_node; /* Node in device tree */
 };
 
@@ -92,12 +95,16 @@ struct gpd_timing_data {
         s64 save_state_latency_ns;
         s64 restore_state_latency_ns;
         s64 effective_constraint_ns;
+        bool constraint_changed;
+        bool cached_stop_ok;
 };
 
 struct generic_pm_domain_data {
         struct pm_domain_data base;
         struct gpd_dev_ops ops;
         struct gpd_timing_data td;
+        struct notifier_block nb;
+        struct mutex lock;
         bool need_restore;
         bool always_on;
 };