PM / Domains: Eliminate the mutex for the generic_pm_domain_data

While adding devices to their PM domains, dev_pm_qos_add_notifier() was
invoked while allocating the generic_pm_domain_data for the device.

Since the generic_pm_domain_data's device pointer will be assigned
after allocation, the ->genpd_dev_pm_qos_notifier() callback could be
called prior having a valid pointer to the device. Similar scenario
existed while removing a device from a genpd.

To cope with these scenarios a mutex was used to protect the pointer to
the device.

By re-order the sequence for when dev_pm_qos_add|remove_notifier() are
invoked, we make sure the ->genpd_dev_pm_qos_notifier() callback are
always called with a valid device pointer available.

In this way, we eliminate the need for protecting the pointer and thus
we can remove the mutex from the struct generic_pm_domain_data.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
index 88198ba919d915d29f5d60f1e42ee405e453a343..1f026c18bc5c6d52f526949680e6d73a84cdfaf4 100644 (file)
--- a/drivers/base/power/domain.c
+++ b/drivers/base/power/domain.c
@@ -344,14 +344,7 @@ static int genpd_dev_pm_qos_notifier(struct notifier_block *nb,
        struct device *dev;
 
        gpd_data = container_of(nb, struct generic_pm_domain_data, nb);
-
-       mutex_lock(&gpd_data->lock);
        dev = gpd_data->base.dev;
-       if (!dev) {
-               mutex_unlock(&gpd_data->lock);
-               return NOTIFY_DONE;
-       }
-       mutex_unlock(&gpd_data->lock);
 
        for (;;) {
                struct generic_pm_domain *genpd;
@@ -1392,16 +1385,12 @@ static struct generic_pm_domain_data *genpd_alloc_dev_data(struct device *dev)
        if (!gpd_data)
                return NULL;
 
-       mutex_init(&gpd_data->lock);
-       gpd_data->nb.notifier_call = genpd_dev_pm_qos_notifier;
-       dev_pm_qos_add_notifier(dev, &gpd_data->nb);
        return gpd_data;
 }
 
 static void genpd_free_dev_data(struct device *dev,
                                struct generic_pm_domain_data *gpd_data)
 {
-       dev_pm_qos_remove_notifier(dev, &gpd_data->nb);
        kfree(gpd_data);
 }
 
@@ -1414,7 +1403,7 @@ static void genpd_free_dev_data(struct device *dev,
 int __pm_genpd_add_device(struct generic_pm_domain *genpd, struct device *dev,
                          struct gpd_timing_data *td)
 {
-       struct generic_pm_domain_data *gpd_data_new, *gpd_data = NULL;
+       struct generic_pm_domain_data *gpd_data;
        int ret = 0;
 
        dev_dbg(dev, "%s()\n", __func__);
@@ -1422,8 +1411,8 @@ int __pm_genpd_add_device(struct generic_pm_domain *genpd, struct device *dev,
        if (IS_ERR_OR_NULL(genpd) || IS_ERR_OR_NULL(dev))
                return -EINVAL;
 
-       gpd_data_new = genpd_alloc_dev_data(dev);
-       if (!gpd_data_new)
+       gpd_data = genpd_alloc_dev_data(dev);
+       if (!gpd_data)
                return -ENOMEM;
 
        genpd_acquire_lock(genpd);
@@ -1445,7 +1434,6 @@ int __pm_genpd_add_device(struct generic_pm_domain *genpd, struct device *dev,
                goto out;
        }
 
-       gpd_data = gpd_data_new;
        dev->power.subsys_data->domain_data = &gpd_data->base;
 
        if (td)
@@ -1461,19 +1449,20 @@ int __pm_genpd_add_device(struct generic_pm_domain *genpd, struct device *dev,
        genpd->device_count++;
        genpd->max_off_time_changed = true;
 
-       mutex_lock(&gpd_data->lock);
        gpd_data->base.dev = dev;
        list_add_tail(&gpd_data->base.list_node, &genpd->dev_list);
        gpd_data->need_restore = -1;
        gpd_data->td.constraint_changed = true;
        gpd_data->td.effective_constraint_ns = -1;
-       mutex_unlock(&gpd_data->lock);
+       gpd_data->nb.notifier_call = genpd_dev_pm_qos_notifier;
 
  out:
        genpd_release_lock(genpd);
 
-       if (gpd_data != gpd_data_new)
-               genpd_free_dev_data(dev, gpd_data_new);
+       if (ret)
+               genpd_free_dev_data(dev, gpd_data);
+       else
+               dev_pm_qos_add_notifier(dev, &gpd_data->nb);
 
        return ret;
 }
@@ -1509,6 +1498,11 @@ int pm_genpd_remove_device(struct generic_pm_domain *genpd,
            ||  pd_to_genpd(dev->pm_domain) != genpd)
                return -EINVAL;
 
+       /* The above validation also means we have existing domain_data. */
+       pdd = dev->power.subsys_data->domain_data;
+       gpd_data = to_gpd_data(pdd);
+       dev_pm_qos_remove_notifier(dev, &gpd_data->nb);
+
        genpd_acquire_lock(genpd);
 
        if (genpd->prepared_count > 0) {
@@ -1525,16 +1519,12 @@ int pm_genpd_remove_device(struct generic_pm_domain *genpd,
        spin_lock_irq(&dev->power.lock);
 
        dev->pm_domain = NULL;
-       pdd = dev->power.subsys_data->domain_data;
        list_del_init(&pdd->list_node);
-       gpd_data = to_gpd_data(pdd);
        dev->power.subsys_data->domain_data = NULL;
 
        spin_unlock_irq(&dev->power.lock);
 
-       mutex_lock(&gpd_data->lock);
        pdd->dev = NULL;
-       mutex_unlock(&gpd_data->lock);
 
        genpd_release_lock(genpd);
 
@@ -1545,6 +1535,7 @@ int pm_genpd_remove_device(struct generic_pm_domain *genpd,
 
  out:
        genpd_release_lock(genpd);
+       dev_pm_qos_add_notifier(dev, &gpd_data->nb);
 
        return ret;
 }

diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
index e160a0bba28d06c11c42320a189aa68de87a0e39..080e778118ba85dfab3a1bd99dd0967917837312 100644 (file)
--- a/include/linux/pm_domain.h
+++ b/include/linux/pm_domain.h
@@ -113,7 +113,6 @@ struct generic_pm_domain_data {
        struct pm_domain_data base;
        struct gpd_timing_data td;
        struct notifier_block nb;
-       struct mutex lock;
        int need_restore;
 };