[S390] dasd: re-initialize read_conf buffer for retries

The buffer for read configuration data has to be initialized with an
EBCDIC string to show support for extended UIDs to z/VM.
If this read configuration data CQR needs to be retried, the buffer
may have changed in between. So re-initialize the buffer to get a
correct extended UID under z/VM.

Signed-off-by: Stefan Haberland <stefan.haberland@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/drivers/s390/block/dasd.c b/drivers/s390/block/dasd.c
index 3b94b65..ce2a780 100644
--- a/drivers/s390/block/dasd.c
+++ b/drivers/s390/block/dasd.c
@@ -2059,13 +2059,14 @@
 /*
  * Wakeup helper for the 'sleep_on' functions.
  */
-static void dasd_wakeup_cb(struct dasd_ccw_req *cqr, void *data)
+void dasd_wakeup_cb(struct dasd_ccw_req *cqr, void *data)
 {
 	spin_lock_irq(get_ccwdev_lock(cqr->startdev->cdev));
 	cqr->callback_data = DASD_SLEEPON_END_TAG;
 	spin_unlock_irq(get_ccwdev_lock(cqr->startdev->cdev));
 	wake_up(&generic_waitq);
 }
+EXPORT_SYMBOL_GPL(dasd_wakeup_cb);
 
 static inline int _wait_for_wakeup(struct dasd_ccw_req *cqr)
 {
@@ -2165,7 +2166,9 @@
 		} else
 			wait_event(generic_waitq, !(device->stopped));
 
-		cqr->callback = dasd_wakeup_cb;
+		if (!cqr->callback)
+			cqr->callback = dasd_wakeup_cb;
+
 		cqr->callback_data = DASD_SLEEPON_START_TAG;
 		dasd_add_request_tail(cqr);
 		if (interruptible) {