[PATCH v2 1/5] ACPI: Enable driver and firmware hints to control power at probe time

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

Allow drivers and firmware tell ACPI that there's no need to power on a
device for probe. This requires both a hint from the firmware as well as
an indication from a driver to leave the device off.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
---
 drivers/acpi/device_pm.c | 15 +++++++++++++--
 include/linux/device.h   |  7 +++++++
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/drivers/acpi/device_pm.c b/drivers/acpi/device_pm.c
index f616b16c1f0be..adcdf78ce4de8 100644
--- a/drivers/acpi/device_pm.c
+++ b/drivers/acpi/device_pm.c
@@ -1276,7 +1276,12 @@ static void acpi_dev_pm_detach(struct device *dev, bool power_off)
 	if (adev && dev->pm_domain == &acpi_general_pm_domain) {
 		dev_pm_domain_set(dev, NULL);
 		acpi_remove_pm_notifier(adev);
-		if (power_off) {
+		if (power_off
+#ifdef CONFIG_PM
+		    && !(dev->driver->probe_low_power &&
+			 device_property_present(dev, "probe-low-power"))
+#endif
+			) {
 			/*
 			 * If the device's PM QoS resume latency limit or flags
 			 * have been exposed to user space, they have to be
@@ -1324,7 +1329,13 @@ int acpi_dev_pm_attach(struct device *dev, bool power_on)
 
 	acpi_add_pm_notifier(adev, dev, acpi_pm_notify_work_func);
 	dev_pm_domain_set(dev, &acpi_general_pm_domain);
-	if (power_on) {
+
+	if (power_on
+#ifdef CONFIG_PM
+	    && !(dev->driver->probe_low_power &&
+		 device_property_present(dev, "probe-low-power"))
+#endif
+		) {
 		acpi_dev_pm_full_power(adev);
 		acpi_device_wakeup_disable(adev);
 	}
diff --git a/include/linux/device.h b/include/linux/device.h
index 6717adee33f01..4bc0ea4a3201a 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -248,6 +248,12 @@ enum probe_type {
  * @owner:	The module owner.
  * @mod_name:	Used for built-in modules.
  * @suppress_bind_attrs: Disables bind/unbind via sysfs.
+ * @probe_low_power: The driver supports its probe function being called while
+ *		     the device is in a low power state, independently of the
+ *		     expected behaviour on combination of a given bus and
+ *		     firmware interface etc. The driver is responsible for
+ *		     powering the device on using runtime PM in such case.
+ *		     This configuration has no effect if CONFIG_PM is disabled.
  * @probe_type:	Type of the probe (synchronous or asynchronous) to use.
  * @of_match_table: The open firmware table.
  * @acpi_match_table: The ACPI match table.
@@ -285,6 +291,7 @@ struct device_driver {
 	const char		*mod_name;	/* used for built-in modules */
 
 	bool suppress_bind_attrs;	/* disables bind/unbind via sysfs */
+	bool probe_low_power;
 	enum probe_type probe_type;
 
 	const struct of_device_id	*of_match_table;
-- 
2.20.1