PM / Domains: Add "wait for parent" status for generic PM domains

The next patch will make it possible for a generic PM domain to have
multiple parents (i.e. multiple PM domains it depends on).  To
prepare for that change it is necessary to change pm_genpd_poweron()
so that it doesn't jump to the start label after running itself
recursively for the parent domain.  For this purpose, introduce a new
PM domain status value GPD_STATE_WAIT_PARENT that will be set by
pm_genpd_poweron() before calling itself recursively for the parent
domain and modify the code in drivers/base/power/domain.c so that
the GPD_STATE_WAIT_PARENT status is guaranteed to be preserved during
the execution of pm_genpd_poweron() for the parent.

This change also causes pm_genpd_add_subdomain() and
pm_genpd_remove_subdomain() to wait for started pm_genpd_poweron() to
complete and allows pm_genpd_runtime_resume() to avoid dropping the
lock after powering on the PM domain.

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

1 files changed, 60 insertions, 30 deletions

diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
index dc423a99c67c..1f4b1326c6a9 100644
--- a/drivers/base/power/domain.c
+++ b/drivers/base/power/domain.c
@@ -81,45 +81,59 @@ static void genpd_set_active(struct generic_pm_domain *genpd)
 }
 
 /**
- * pm_genpd_poweron - Restore power to a given PM domain and its parents.
+ * __pm_genpd_poweron - Restore power to a given PM domain and its parents.
  * @genpd: PM domain to power up.
  *
  * Restore power to @genpd and all of its parents so that it is possible to
  * resume a device belonging to it.
  */
-int pm_genpd_poweron(struct generic_pm_domain *genpd)
+int __pm_genpd_poweron(struct generic_pm_domain *genpd)
+        __releases(&genpd->lock) __acquires(&genpd->lock)
 {
-        struct generic_pm_domain *parent;
+        DEFINE_WAIT(wait);
         int ret = 0;
 
-        mutex_lock(&genpd->lock);
+        /* If the domain's parent is being waited for, we have to wait too. */
+        for (;;) {
+                prepare_to_wait(&genpd->status_wait_queue, &wait,
+                                TASK_UNINTERRUPTIBLE);
+                if (genpd->status != GPD_STATE_WAIT_PARENT)
+                        break;
+                mutex_unlock(&genpd->lock);
 
-        parent = genpd->parent;
+                schedule();
+
+                mutex_lock(&genpd->lock);
+        }
+        finish_wait(&genpd->status_wait_queue, &wait);
 
- start:
         if (genpd->status == GPD_STATE_ACTIVE
             || (genpd->prepared_count > 0 && genpd->suspend_power_off))
-                goto out;
+                return 0;
 
         if (genpd->status != GPD_STATE_POWER_OFF) {
                 genpd_set_active(genpd);
-                goto out;
+                return 0;
         }
 
-        if (parent) {
-                genpd_sd_counter_inc(parent);
+        if (genpd->parent) {
+                genpd_sd_counter_inc(genpd->parent);
+                genpd->status = GPD_STATE_WAIT_PARENT;
 
                 mutex_unlock(&genpd->lock);
 
-                ret = pm_genpd_poweron(parent);
+                ret = pm_genpd_poweron(genpd->parent);
 
                 mutex_lock(&genpd->lock);
 
+                /*
+                 * The "wait for parent" status is guaranteed not to change
+                 * while the parent is powering on.
+                 */
+                genpd->status = GPD_STATE_POWER_OFF;
+                wake_up_all(&genpd->status_wait_queue);
                 if (ret)
                         goto err;
-
-                parent = NULL;
-                goto start;
         }
 
         if (genpd->power_on) {
@@ -130,16 +144,27 @@ int pm_genpd_poweron(struct generic_pm_domain *genpd)
 
         genpd_set_active(genpd);
 
- out:
-        mutex_unlock(&genpd->lock);
-
-        return ret;
+        return 0;
 
  err:
         if (genpd->parent)
                 genpd_sd_counter_dec(genpd->parent);
 
-        goto out;
+        return ret;
+}
+
+/**
+ * pm_genpd_poweron - Restore power to a given PM domain and its parents.
+ * @genpd: PM domain to power up.
+ */
+int pm_genpd_poweron(struct generic_pm_domain *genpd)
+{
+        int ret;
+
+        mutex_lock(&genpd->lock);
+        ret = __pm_genpd_poweron(genpd);
+        mutex_unlock(&genpd->lock);
+        return ret;
 }
 
 #endif /* CONFIG_PM */
@@ -225,7 +250,8 @@ static void __pm_genpd_restore_device(struct dev_list_entry *dle,
  */
 static bool genpd_abort_poweroff(struct generic_pm_domain *genpd)
 {
-        return genpd->status == GPD_STATE_ACTIVE || genpd->resume_count > 0;
+        return genpd->status == GPD_STATE_WAIT_PARENT
+                || genpd->status == GPD_STATE_ACTIVE || genpd->resume_count > 0;
 }
 
 /**
@@ -261,11 +287,13 @@ static int pm_genpd_poweroff(struct generic_pm_domain *genpd)
         /*
          * Do not try to power off the domain in the following situations:
          * (1) The domain is already in the "power off" state.
-         * (2) System suspend is in progress.
+         * (2) The domain is waiting for its parent to power up.
          * (3) One of the domain's devices is being resumed right now.
+         * (4) System suspend is in progress.
          */
-        if (genpd->status == GPD_STATE_POWER_OFF || genpd->prepared_count > 0
-            || genpd->resume_count > 0)
+        if (genpd->status == GPD_STATE_POWER_OFF
+            || genpd->status == GPD_STATE_WAIT_PARENT
+            || genpd->resume_count > 0 || genpd->prepared_count > 0)
                 return 0;
 
         if (atomic_read(&genpd->sd_count) > 0)
@@ -299,14 +327,15 @@ static int pm_genpd_poweroff(struct generic_pm_domain *genpd)
         list_for_each_entry_reverse(dle, &genpd->dev_list, node) {
                 ret = atomic_read(&genpd->sd_count) == 0 ?
                         __pm_genpd_save_device(dle, genpd) : -EBUSY;
+
+                if (genpd_abort_poweroff(genpd))
+                        goto out;
+
                 if (ret) {
                         genpd_set_active(genpd);
                         goto out;
                 }
 
-                if (genpd_abort_poweroff(genpd))
-                        goto out;
-
                 if (genpd->status == GPD_STATE_REPEAT) {
                         genpd->poweroff_task = NULL;
                         goto start;
@@ -432,11 +461,12 @@ static int pm_genpd_runtime_resume(struct device *dev)
         if (IS_ERR(genpd))
                 return -EINVAL;
 
-        ret = pm_genpd_poweron(genpd);
-        if (ret)
-                return ret;
-
         mutex_lock(&genpd->lock);
+        ret = __pm_genpd_poweron(genpd);
+        if (ret) {
+                mutex_unlock(&genpd->lock);
+                return ret;
+        }
         genpd->status = GPD_STATE_BUSY;
         genpd->resume_count++;
         for (;;) {