s390: cio: Delay uevents for subchannels

We often have the situation that we register a subchannel and start device
recognition, only to find out that the device is not usable after all, which
triggers an unregister of the subchannel.  This often happens on hundreds of
subchannels on a LPAR, leading to a storm of events which aren't of any use. 
Therefore, use uevent_suppress to delay the KOBJ_ADD uevent for a subchannel
until we know that its ccw_device is to be registered.
Signed-off-by: NCornelia Huck <cornelia.huck@de.ibm.com>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: Eric Rannaud <eric.rannaud@gmail.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/s390/cio/device.c

@@ -871,6 +871,12 @@ io_subchannel_register(struct work_struct *work)
 		}
 		goto out;
 	}
+	/*
+	 * Now we know this subchannel will stay, we can throw
+	 * our delayed uevent.
+	 */
+	sch->dev.uevent_suppress = 0;
+	kobject_uevent(&sch->dev.kobj, KOBJ_ADD);
 	/* make it known to the system */
 	ret = ccw_device_register(cdev);
 	if (ret) {