s390/kdump: Clear subchannel ID to signal non-CCW/SCSI IPL

For CCW and SCSI IPL the hardware sets the subchannel ID and number
correctly at 0xb8. For kdump at 0xb8 normally there is the data of
the previously IPLed system.

In order to be clean now for kdump and kexec always set the subchannel
ID and number to zero. This tells the next OS that no CCW/SCSI IPL
has been done.
Reviewed-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/ipl.c

@@ -2060,6 +2060,13 @@ void s390_reset_system(void (*func)(void *), void *data)
 	S390_lowcore.program_new_psw.addr =
 		PSW_ADDR_AMODE | (unsigned long) s390_base_pgm_handler;
 
+	/*
+	 * Clear subchannel ID and number to signal new kernel that no CCW or
+	 * SCSI IPL has been done (for kexec and kdump)
+	 */
+	S390_lowcore.subchannel_id = 0;
+	S390_lowcore.subchannel_nr = 0;
+
 	/* Store status at absolute zero */
 	store_status();