[PATCH] PM / Domains: Add pm_genpd_lookup() API to lookup domain by device node

[Ulf Hansson]

In a step to move away from using genpd's name based APIs, such as the
pm_genpd_add_subdomain_names(), provide an API to lookup an already
initialized generic PM domain by its device node.

This API would typically be a called from SOC specific code, to fetch a
handle to the domain. Especially convenient to configure subdomains and
when the hierarchy of the domains are described in DT.

Do note, before pm_genpd_init() is invoked to initialize a generic PM
domain, it's the callers responsibility to assign the new ->dev_node
pointer in the struct generic_pm_domain, to enable pm_genpd_lookup() to
find the domain.

Signed-off-by: Ulf Hansson <ulf.hansson at linaro.org>
---

The background to why I propose this patch comes from a discussion around the
below patchset:
https://lkml.org/lkml/2014/11/24/290


---
 drivers/base/power/domain.c | 26 ++++++++++++++++++++++++++
 include/linux/pm_domain.h   |  2 ++
 2 files changed, 28 insertions(+)

diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
index 735c473..34555eb 100644
--- a/drivers/base/power/domain.c
+++ b/drivers/base/power/domain.c
@@ -75,6 +75,32 @@ struct generic_pm_domain *dev_to_genpd(struct device *dev)
 	return pd_to_genpd(dev->pm_domain);
 }
 
+/**
+ * pm_genpd_lookup - Fetch a generic PM domain object by device node
+ * @node: Device node to a corresponding genpd.
+ *
+ * Returns a valid pointer to struct generic_pm_domain on success or ERR_PTR()
+ * on failure.
+ */
+struct generic_pm_domain *pm_genpd_lookup(struct device_node *node)
+{
+	struct generic_pm_domain *genpd = ERR_PTR(-ENOENT), *gpd;
+
+	if (IS_ERR_OR_NULL(node))
+		return ERR_PTR(-EINVAL);
+
+	mutex_lock(&gpd_list_lock);
+	list_for_each_entry(gpd, &gpd_list, gpd_list_node) {
+		if (gpd->dev_node == node) {
+			genpd = gpd;
+			break;
+		}
+	}
+	mutex_unlock(&gpd_list_lock);
+	return genpd;
+}
+EXPORT_SYMBOL_GPL(pm_genpd_lookup);
+
 static int genpd_stop_dev(struct generic_pm_domain *genpd, struct device *dev)
 {
 	return GENPD_DEV_TIMED_CALLBACK(genpd, int, stop, dev,
diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
index 8cbd32e..322cb7c 100644
--- a/include/linux/pm_domain.h
+++ b/include/linux/pm_domain.h
@@ -53,6 +53,7 @@ struct generic_pm_domain {
 	struct dev_power_governor *gov;
 	struct work_struct power_off_work;
 	const char *name;
+	struct device_node *dev_node;	/* Device node for the PM domain */
 	unsigned int in_progress;	/* Number of devices being suspended now */
 	atomic_t sd_count;	/* Number of subdomains with power "on" */
 	enum gpd_status status;	/* Current state of the domain */
@@ -126,6 +127,7 @@ static inline struct generic_pm_domain_data *dev_gpd_data(struct device *dev)
 }
 
 extern struct generic_pm_domain *dev_to_genpd(struct device *dev);
+extern struct generic_pm_domain *pm_genpd_lookup(struct device_node *node);
 extern int __pm_genpd_add_device(struct generic_pm_domain *genpd,
 				 struct device *dev,
 				 struct gpd_timing_data *td);
-- 
1.9.1