[S390] smp: always reboot on cpu 0

Always reboot on logical cpu 0. This makes sure that the IPL cpu is
always the same and usually avoids strange numbering schemes between
physical and logical cpus.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/switch_cpu64.S

@@ -0,0 +1,52 @@
+/*
+ * 64-bit switch cpu code
+ *
+ * Copyright IBM Corp. 2009
+ *
+ */
+
+#include <asm/asm-offsets.h>
+#include <asm/lowcore.h>
+#include <asm/ptrace.h>
+
+# smp_switch_to_cpu switches to destination cpu and executes the passed function
+# Parameter: %r2 - function to call
+#	     %r3 - function parameter
+#	     %r4 - stack poiner
+#	     %r5 - current cpu
+#	     %r6 - destination cpu
+
+	.section .text
+	.align 4
+	.globl smp_switch_to_cpu
+smp_switch_to_cpu:
+	stmg	%r6,%r15,__SF_GPRS(%r15)
+	lgr	%r1,%r15
+	aghi	%r15,-STACK_FRAME_OVERHEAD
+	stg	%r1,__SF_BACKCHAIN(%r15)
+	larl	%r1,.gprregs
+	stmg	%r0,%r15,0(%r1)
+1:	sigp	%r0,%r6,__SIGP_RESTART	/* start destination CPU */
+	brc	2,1b			/* busy, try again */
+2:	sigp	%r0,%r5,__SIGP_STOP	/* stop current CPU */
+	brc	2,2b			/* busy, try again */
+3:	j	3b
+
+	.globl	smp_restart_cpu
+smp_restart_cpu:
+	larl	%r1,.gprregs
+	lmg	%r0,%r15,0(%r1)
+1:	sigp	%r0,%r5,__SIGP_SENSE	/* Wait for calling CPU */
+	brc	10,1b			/* busy, accepted (status 0), running */
+	tmll	%r0,0x40		/* Test if calling CPU is stopped */
+	jz	1b
+	ltgr	%r4,%r4			/* New stack ? */
+	jz	1f
+	lgr	%r15,%r4
+1:	basr	%r14,%r2
+
+	.section .data,"aw",@progbits
+.gprregs:
+	.rept	16
+	.quad	0
+	.endr