soundwire: bus_type: add DPM_FLAG_SMART_SUSPEND support

Where the SoundWire manager is pm_runtime suspended with the
clock-stop mode enabled, we currently do nothing on Intel platforms
before entering system suspend.

This is problematic since the hardware does not seem to fully reset
during system resume, we have e.g. been tracking issues related to
this clock stop mode for the last 6 months.

The power management framework already defines a
DPM_FLAG_SMART_SUSPEND flag. This patch exposes a bus .suspend
callback that will handle a pm_runtime_resume when this flag is not
set.

FIXME: need to find a way to set this flag or not depending on parent
capabilities.

BugLink: thesofproject#2606
Suggested-by: Rafael J. Wysocki <rafael@kernel.org>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>

drivers/soundwire/bus_type.c

@@ -4,6 +4,7 @@
 #include <linux/module.h>
 #include <linux/mod_devicetable.h>
 #include <linux/pm_domain.h>
+#include <linux/pm_runtime.h>
 #include <linux/soundwire/sdw.h>
 #include <linux/soundwire/sdw_type.h>
 #include "bus.h"
@@ -71,9 +72,31 @@ int sdw_slave_uevent(struct device *dev, struct kobj_uevent_env *env)
 	return 0;
 }
 
+static int __maybe_unused sdw_slave_suspend(struct device *dev)
+{
+	int (*callback)(struct device *) = NULL;
+	int ret = 0;
+
+	if (!dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND))
+		pm_runtime_resume(dev);
+
+	if (dev->driver && dev->driver->pm)
+		callback = dev->driver->pm->suspend;
+
+	if (callback)
+		ret = callback(dev);
+
+	return ret;
+}
+
+static const struct dev_pm_ops sdw_bus_pm_ops = {
+	SET_SYSTEM_SLEEP_PM_OPS(sdw_slave_suspend, NULL)
+};
+
 struct bus_type sdw_bus_type = {
 	.name = "soundwire",
 	.match = sdw_bus_match,
+	.pm = &sdw_bus_pm_ops
 };
 EXPORT_SYMBOL_GPL(sdw_bus_type);