PM / Domains: Do not take parent locks to modify subdomain counters

After the subdomain counter in struct generic_pm_domain has been
changed into an atomic_t field, it is possible to modify
pm_genpd_poweron() and pm_genpd_poweroff() so that they don't take
the parents locks.  This requires pm_genpd_poweron() to increment
the parent's subdomain counter before calling itself recursively
for the parent and to decrement it if an error is to be returned.

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

diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
index 20e2b52..ef25b6f 100644 (file)
--- a/drivers/base/power/domain.c
+++ b/drivers/base/power/domain.c
@@ -93,12 +93,7 @@ int pm_genpd_poweron(struct generic_pm_domain *genpd)
        int ret = 0;
 
  start:
-       if (parent) {
-               genpd_acquire_lock(parent);
-               mutex_lock_nested(&genpd->lock, SINGLE_DEPTH_NESTING);
-       } else {
-               mutex_lock(&genpd->lock);
-       }
+       mutex_lock(&genpd->lock);
 
        if (genpd->status == GPD_STATE_ACTIVE
            || (genpd->prepared_count > 0 && genpd->suspend_power_off))
@@ -109,31 +104,33 @@ int pm_genpd_poweron(struct generic_pm_domain *genpd)
                goto out;
        }
 
-       if (parent && parent->status != GPD_STATE_ACTIVE) {
+       if (parent) {
+               genpd_sd_counter_inc(parent);
+
                mutex_unlock(&genpd->lock);
-               genpd_release_lock(parent);
 
                ret = pm_genpd_poweron(parent);
-               if (ret)
+               if (ret) {
+                       genpd_sd_counter_dec(parent);
                        return ret;
+               }
 
+               parent = NULL;
                goto start;
        }
 
-       if (genpd->power_on) {
+       if (genpd->power_on)
                ret = genpd->power_on(genpd);
-               if (ret)
-                       goto out;
-       }
 
-       genpd_set_active(genpd);
-       if (parent)
-               genpd_sd_counter_inc(parent);
+       if (ret) {
+               if (genpd->parent)
+                       genpd_sd_counter_dec(genpd->parent);
+       } else {
+               genpd_set_active(genpd);
+       }
 
  out:
        mutex_unlock(&genpd->lock);
-       if (parent)
-               genpd_release_lock(parent);
 
        return ret;
 }
@@ -293,7 +290,8 @@ static int pm_genpd_poweroff(struct generic_pm_domain *genpd)
        genpd->poweroff_task = current;
 
        list_for_each_entry_reverse(dle, &genpd->dev_list, node) {
-               ret = __pm_genpd_save_device(dle, genpd);
+               ret = atomic_read(&genpd->sd_count) == 0 ?
+                       __pm_genpd_save_device(dle, genpd) : -EBUSY;
                if (ret) {
                        genpd_set_active(genpd);
                        goto out;
@@ -308,38 +306,32 @@ static int pm_genpd_poweroff(struct generic_pm_domain *genpd)
                }
        }
 
-       parent = genpd->parent;
-       if (parent) {
-               mutex_unlock(&genpd->lock);
-
-               genpd_acquire_lock(parent);
-               mutex_lock_nested(&genpd->lock, SINGLE_DEPTH_NESTING);
-
-               if (genpd_abort_poweroff(genpd)) {
-                       genpd_release_lock(parent);
+       if (genpd->power_off) {
+               if (atomic_read(&genpd->sd_count) > 0) {
+                       ret = -EBUSY;
                        goto out;
                }
-       }
 
-       if (genpd->power_off) {
+               /*
+                * If sd_count > 0 at this point, one of the children hasn't
+                * managed to call pm_genpd_poweron() for the parent yet after
+                * incrementing it.  In that case pm_genpd_poweron() will wait
+                * for us to drop the lock, so we can call .power_off() and let
+                * the pm_genpd_poweron() restore power for us (this shouldn't
+                * happen very often).
+                */
                ret = genpd->power_off(genpd);
                if (ret == -EBUSY) {
                        genpd_set_active(genpd);
-                       if (parent)
-                               genpd_release_lock(parent);
-
                        goto out;
                }
        }
 
        genpd->status = GPD_STATE_POWER_OFF;
 
-       if (parent) {
-               if (genpd_sd_counter_dec(parent))
-                       genpd_queue_power_off_work(parent);
-
-               genpd_release_lock(parent);
-       }
+       parent = genpd->parent;
+       if (parent && genpd_sd_counter_dec(parent))
+               genpd_queue_power_off_work(parent);
 
  out:
        genpd->poweroff_task = NULL;