PM: Allow SCSI devices to suspend/resume asynchronously

Set power.async_suspend for all SCSI devices, targets and hosts, so
that they can be suspended and resumed in parallel with the main
suspend/resume thread and possibly with other devices they don't
depend on in a known way (i.e. devices which are not their parents or
children).

The power.async_suspend flag is also set for devices that don't have
suspend or resume callbacks, because otherwise they would make the
main suspend/resume thread wait for their "asynchronous" children
(during suspend) or parents (during resume), effectively negating the
possible gains from executing these devices' suspend and resume
callbacks asynchronously.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

drivers/scsi/hosts.c

@@ -215,6 +215,8 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
 		shost->shost_gendev.parent = dev ? dev : &platform_bus;
 	shost->dma_dev = dma_dev;
 
+	device_enable_async_suspend(&shost->shost_gendev);
+
 	error = device_add(&shost->shost_gendev);
 	if (error)
 		goto out;
@@ -222,6 +224,8 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
 	scsi_host_set_state(shost, SHOST_RUNNING);
 	get_device(shost->shost_gendev.parent);
 
+	device_enable_async_suspend(&shost->shost_dev);
+
 	error = device_add(&shost->shost_dev);
 	if (error)
 		goto out_del_gendev;

drivers/scsi/scsi_sysfs.c

@@ -847,6 +847,8 @@ static int scsi_target_add(struct scsi_target *starget)
 	if (starget->state != STARGET_CREATED)
 		return 0;
 
+	device_enable_async_suspend(&starget->dev);
+
 	error = device_add(&starget->dev);
 	if (error) {
 		dev_err(&starget->dev, "target device_add failed, error %d\n", error);
@@ -886,11 +888,13 @@ int scsi_sysfs_add_sdev(struct scsi_device *sdev)
 		return error;
 
 	transport_configure_device(&starget->dev);
+	device_enable_async_suspend(&sdev->sdev_gendev);
 	error = device_add(&sdev->sdev_gendev);
 	if (error) {
 		printk(KERN_INFO "error 1\n");
 		goto out_remove;
 	}
+	device_enable_async_suspend(&sdev->sdev_dev);
 	error = device_add(&sdev->sdev_dev);
 	if (error) {
 		printk(KERN_INFO "error 2\n");