pmdomain: core: introduce dev_pm_genpd_is_on()

This helper function returns the current power status of a given generic
power domain.

As example, remoteproc/imx_rproc.c can now use this function to check
the power status of the remote core to properly set "attached" or
"offline" modes.

Suggested-by: Ulf Hansson <[e-mail]>
Reviewed-by: Bjorn Andersson <[e-mail]>
Reviewed-by: Peng Fan <[e-mail]>
Signed-off-by: Hiago De Franco <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Ulf Hansson <[e-mail]>

drivers/pmdomain/core.c

···
 EXPORT_SYMBOL_GPL(dev_pm_genpd_rpm_always_on);
 
 /**
+ * dev_pm_genpd_is_on() - Get device's current power domain status
+ *
+ * @dev: Device to get the current power status
+ *
+ * This function checks whether the generic power domain associated with the
+ * given device is on or not by verifying if genpd_status_on equals
+ * GENPD_STATE_ON.
+ *
+ * Note: this function returns the power status of the genpd at the time of the
+ * call. The power status may change after due to activity from other devices
+ * sharing the same genpd. Therefore, this information should not be relied for
+ * long-term decisions about the device power state.
+ *
+ * Return: 'true' if the device's power domain is on, 'false' otherwise.
+ */
+bool dev_pm_genpd_is_on(struct device *dev)
+{
+	struct generic_pm_domain *genpd;
+	bool is_on;
+
+	genpd = dev_to_genpd_safe(dev);
+	if (!genpd)
+		return false;
+
+	genpd_lock(genpd);
+	is_on = genpd_status_on(genpd);
+	genpd_unlock(genpd);
+
+	return is_on;
+}
+EXPORT_SYMBOL_GPL(dev_pm_genpd_is_on);
+
+/**
  * pm_genpd_inc_rejected() - Adjust the rejected/usage counts for an idle-state.
  *
  * @genpd: The PM domain the idle-state belongs to.

include/linux/pm_domain.h

···
 int dev_pm_genpd_set_hwmode(struct device *dev, bool enable);
 bool dev_pm_genpd_get_hwmode(struct device *dev);
 int dev_pm_genpd_rpm_always_on(struct device *dev, bool on);
+bool dev_pm_genpd_is_on(struct device *dev);
 
 extern struct dev_power_governor simple_qos_governor;
 extern struct dev_power_governor pm_domain_always_on_gov;
···
 static inline int dev_pm_genpd_rpm_always_on(struct device *dev, bool on)
 {
 	return -EOPNOTSUPP;
+}
+
+static inline bool dev_pm_genpd_is_on(struct device *dev)
+{
+	return false;
 }
 
 #define simple_qos_governor		(*(struct dev_power_governor *)(NULL))