[PATCH v8 3/6] ACPI: Add a convenience function to tell a device is in low power state

[Sakari Ailus <sakari.ailus@linux.intel.com>]

Add a convenience function to tell whether a device is in low power state,
primarily for use in drivers' probe or remove functions on busses where
the custom is to power on the device for the duration of both.

Returns false on non-ACPI systems.

Suggested-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 drivers/acpi/device_pm.c | 31 +++++++++++++++++++++++++++++++
 include/linux/acpi.h     |  5 +++++
 2 files changed, 36 insertions(+)

diff --git a/drivers/acpi/device_pm.c b/drivers/acpi/device_pm.c
index 94d91c67aeaeb..e3c488d4af0d4 100644
--- a/drivers/acpi/device_pm.c
+++ b/drivers/acpi/device_pm.c
@@ -1344,4 +1344,35 @@ int acpi_dev_pm_attach(struct device *dev, bool power_on)
 	return 1;
 }
 EXPORT_SYMBOL_GPL(acpi_dev_pm_attach);
+
+/**
+ * acpi_dev_state_low_power - Check the current ACPI power state of a device.
+ * @dev: Physical device the ACPI power state of which to check
+ *
+ * On a system without ACPI, return false. On a system with ACPI, return true if
+ * the current ACPI power state of the device is not D0, or false otherwise.
+ *
+ * Note that the power state of a device is not well-defined after it has been
+ * passed to acpi_device_set_power() and before that function returns, so it is
+ * not valid to ask for the ACPI power state of the device in that time frame.
+ */
+bool acpi_dev_state_low_power(struct device *dev)
+{
+	struct acpi_device *adev = ACPI_COMPANION(dev);
+	int power_state;
+	int ret;
+
+	if (!adev)
+		return false;
+
+	ret = acpi_device_get_power(adev, &power_state);
+	if (ret) {
+		dev_dbg(dev, "Cannot obtain power state (%d)\n", ret);
+		return false;
+	}
+
+	return power_state != ACPI_STATE_D0;
+}
+EXPORT_SYMBOL_GPL(acpi_dev_state_low_power);
+
 #endif /* CONFIG_PM */
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 17e80e182802e..d76d851259a49 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -978,6 +978,7 @@ int acpi_dev_resume(struct device *dev);
 int acpi_subsys_runtime_suspend(struct device *dev);
 int acpi_subsys_runtime_resume(struct device *dev);
 int acpi_dev_pm_attach(struct device *dev, bool power_on);
+bool acpi_dev_state_low_power(struct device *dev);
 #else
 static inline int acpi_dev_runtime_suspend(struct device *dev) { return 0; }
 static inline int acpi_dev_runtime_resume(struct device *dev) { return 0; }
@@ -987,6 +988,10 @@ static inline int acpi_dev_pm_attach(struct device *dev, bool power_on)
 {
 	return 0;
 }
+static inline bool acpi_dev_state_low_power(struct device *dev)
+{
+	return false;
+}
 #endif
 
 #if defined(CONFIG_ACPI) && defined(CONFIG_PM_SLEEP)
-- 
2.20.1