soundwire: master: use pm_runtime_set_active() on add

The 'master' device acts as a glue layer used during bus
initialization only, and it needs to be 'transparent' for pm_runtime
management. Its behavior should be that it becomes active when one of
its children becomes active, and suspends when all of its children are
suspended.

In our tests on Intel platforms, we routinely see these sort of
warnings on the initial boot:

[ 21.447345] rt715 sdw:3:25d:715:0: runtime PM trying to activate
child device sdw:3:25d:715:0 but parent (sdw-master-3) is not active

This is root-caused to a missing setup to make the device 'active' on
probe. Since we don't want the device to remain active forever after
the probe, the autosuspend configuration is also enabled at the end of
the probe - the device will actually autosuspend only in the case
where there are no devices physically attached. In practice, the
master device will suspend when all its children are no longer active.

Fixes: bd84256e ('soundwire: master: enable pm runtime')
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Rander Wang <rander.wang@linux.intel.com>
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Link: https://lore.kernel.org/r/20201124130742.10986-1-yung-chuan.liao@linux.intel.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/soundwire/master.c

@@ -8,6 +8,15 @@
 #include <linux/soundwire/sdw_type.h>
 #include "bus.h"
 
+/*
+ * The 3s value for autosuspend will only be used if there are no
+ * devices physically attached on a bus segment. In practice enabling
+ * the bus operation will result in children devices become active and
+ * the master device will only suspend when all its children are no
+ * longer active.
+ */
+#define SDW_MASTER_SUSPEND_DELAY_MS 3000
+
 /*
  * The sysfs for properties reflects the MIPI description as given
  * in the MIPI DisCo spec
@@ -154,7 +163,12 @@ int sdw_master_device_add(struct sdw_bus *bus, struct device *parent,
 	bus->dev = &md->dev;
 	bus->md = md;
 
+	pm_runtime_set_autosuspend_delay(&bus->md->dev, SDW_MASTER_SUSPEND_DELAY_MS);
+	pm_runtime_use_autosuspend(&bus->md->dev);
+	pm_runtime_mark_last_busy(&bus->md->dev);
+	pm_runtime_set_active(&bus->md->dev);
 	pm_runtime_enable(&bus->md->dev);
+	pm_runtime_idle(&bus->md->dev);
 device_register_err:
 	return ret;
 }