[RFC PATCH 8/8] PM / Domains: Add support for removing PM domains

[Jon Hunter]

The genpd framework allows users to add PM domains via the pm_genpd_init()
function, however, there is no corresponding function to remove a PM
domain. For most devices this may be fine as the PM domains are never
removed, however, for devices that wish to populate the PM domains from
within a driver, having the ability to remove a PM domain if the probing
of the device fails or the driver is unloaded is necessary.

Add the function pm_genpd_remove() to remove a PM domain by referencing
it's generic_pm_domain structure.

If a device supports nested or subdomains, then the PM domains
should be removed in reverse order to ensure that the subdomains are
removed first. Hence, add the function pm_genpd_remove_tail() to remove
the last PM domain added by a given provider and return the
generic_pm_domain structure for the PM domain that was removed.

PM domains can only be removed if they are not a parent domain to
another PM domain and have no devices associated with them.

When removing PM domains, the PM domain will also be removed from the
list of providers, if it was registered.

Signed-off-by: Jon Hunter <jonathanh at nvidia.com>
---
 drivers/base/power/domain.c | 96 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/pm_domain.h   | 12 ++++++
 2 files changed, 108 insertions(+)

diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
index 9b33377bf01b..17090e1c91d6 100644
--- a/drivers/base/power/domain.c
+++ b/drivers/base/power/domain.c
@@ -1556,6 +1556,102 @@ void pm_genpd_init(struct generic_pm_domain *genpd,
 }
 EXPORT_SYMBOL_GPL(pm_genpd_init);
 
+/**
+ * __pm_genpd_remove - Remove a generic I/O PM domain
+ * @genpd: Pointer to PM domain that is to be removed.
+ *
+ * To remove the PM domain, this function:
+ *  - Removes the PM domain from the list of providers, if registered.
+ *  - Removes the PM domain as a subdomain to any parent domains,
+ *    if it was added.
+ *  - Removes the PM domain from the list of registered PM domains.
+ *
+ * The PM domain will only be removed, if it is not a parent to any
+ * other PM domain and has no devices associated with it. Must be called
+ * with the gpd_list_lock held.
+ */
+static int __pm_genpd_remove(struct generic_pm_domain *genpd)
+{
+	struct gpd_link *l, *link;
+	int ret = 0;
+
+	if (IS_ERR_OR_NULL(genpd))
+		return -EINVAL;
+
+	if (genpd->provider_data)
+		of_genpd_del_provider_by_data(genpd->provider_data);
+
+	mutex_lock(&genpd->lock);
+
+	if (!list_empty(&genpd->master_links) || genpd->device_count) {
+		mutex_unlock(&genpd->lock);
+		pr_err("%s: unable to remove %s\n", __func__, genpd->name);
+		return -EBUSY;
+	}
+
+	list_for_each_entry_safe(link, l, &genpd->slave_links, slave_node) {
+		list_del(&link->master_node);
+		list_del(&link->slave_node);
+		kfree(link);
+	}
+
+	list_del(&genpd->gpd_list_node);
+	mutex_unlock(&genpd->lock);
+	cancel_work_sync(&genpd->power_off_work);
+	pr_debug("%s: removed %s\n", __func__, genpd->name);
+
+	return ret;
+}
+
+/**
+ * pm_genpd_remove - Remove a generic I/O PM domain
+ * @genpd: Pointer to PM domain that is to be removed.
+ */
+int pm_genpd_remove(struct generic_pm_domain *genpd)
+{
+	int ret;
+
+	mutex_lock(&gpd_list_lock);
+	ret = __pm_genpd_remove(genpd);
+	mutex_unlock(&gpd_list_lock);
+
+	return ret;
+}
+
+/**
+ * pm_genpd_remove_tail - Remove the last PM domain registered for a provider
+ * @provider: Pointer to device structure associated with provider
+ *
+ * Find the last PM domain that was added by the provider whose 'provider'
+ * device structure matches the device structure given. The 'provider'
+ * device structure for a given PM domain should be initialised by the
+ * device that is creating the PM domains and hence, calling
+ * pm_genpd_init().
+ *
+ * Returns a valid pointer to struct generic_pm_domain on success or
+ * ERR_PTR() on failure.
+ */
+struct generic_pm_domain *pm_genpd_remove_tail(struct device *provider)
+{
+	struct generic_pm_domain *g, *gpd, *genpd = ERR_PTR(-ENOENT);
+	int ret;
+
+	if (IS_ERR_OR_NULL(provider))
+		return ERR_PTR(-EINVAL);
+
+	mutex_lock(&gpd_list_lock);
+	list_for_each_entry_safe(gpd, g, &gpd_list, gpd_list_node) {
+		if (gpd->provider == provider) {
+			ret = __pm_genpd_remove(gpd);
+			genpd = ret ? ERR_PTR(ret) : gpd;
+			break;
+		}
+	}
+	mutex_unlock(&gpd_list_lock);
+
+	return genpd;
+}
+
 #ifdef CONFIG_PM_GENERIC_DOMAINS_OF
 /*
  * Device Tree based PM domain providers.
diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
index 7b7921a65cb0..78b23718392f 100644
--- a/include/linux/pm_domain.h
+++ b/include/linux/pm_domain.h
@@ -53,6 +53,7 @@ struct generic_pm_domain {
 	struct mutex lock;
 	struct dev_power_governor *gov;
 	struct work_struct power_off_work;
+	struct device *provider;	/* Identity of the domain provider */
 	void *provider_data;
 	const char *name;
 	atomic_t sd_count;	/* Number of subdomains with power "on" */
@@ -132,6 +133,8 @@ extern int pm_genpd_remove_subdomain(struct generic_pm_domain *genpd,
 				     struct generic_pm_domain *target);
 extern void pm_genpd_init(struct generic_pm_domain *genpd,
 			  struct dev_power_governor *gov, bool is_off);
+extern int pm_genpd_remove(struct generic_pm_domain *genpd);
+extern struct generic_pm_domain *pm_genpd_remove_tail(struct device *provider);
 
 extern struct dev_power_governor simple_qos_governor;
 extern struct dev_power_governor pm_domain_always_on_gov;
@@ -166,6 +169,15 @@ static inline void pm_genpd_init(struct generic_pm_domain *genpd,
 				 struct dev_power_governor *gov, bool is_off)
 {
 }
+static inline int pm_genpd_remove(struct generic_pm_domain *genpd)
+{
+	return -ENOTSUPP;
+}
+static inline
+struct generic_pm_domain *pm_genpd_remove_tail(struct device *provider)
+{
+	return ERR_PTR(-ENOTSUPP);
+}
 #endif
 
 static inline int pm_genpd_add_device(struct generic_pm_domain *genpd,
-- 
2.1.4