[POWERPC] Make iSeries spin on __secondary_hold_spinloop, like pSeries

Currently all iSeries secondary CPUs spin directly on the cpu_start
field in their paca.  Make them spin on the global
__secondary_hold_spinloop until after the pacas have been initialised.

As Stephen Rothwell points out, this works at the moment because
__secondary_hold_spinloop is being set already, but iSeries isn't
looking at it :)
Signed-off-by: Tony Breeds <tony@bakeyournoodle.com>
Acked-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/platforms/iseries/exception.S

@@ -59,8 +59,33 @@ system_reset_iSeries:
 	andc	r4,r4,r5
 	mtspr	SPRN_CTRLT,r4
 
+/* Spin on __secondary_hold_spinloop until it is updated by the boot cpu. */
+/* In the UP case we'll yeild() later, and we will not access the paca anyway */
+#ifdef CONFIG_SMP
 1:
 	HMT_LOW
+	LOAD_REG_IMMEDIATE(r23, __secondary_hold_spinloop)
+	ld	r23,0(r23)
+	sync
+	LOAD_REG_IMMEDIATE(r3,current_set)
+	sldi	r28,r24,3		/* get current_set[cpu#] */
+	ldx	r3,r3,r28
+	addi	r1,r3,THREAD_SIZE
+	subi	r1,r1,STACK_FRAME_OVERHEAD
+
+	cmpwi	0,r23,0			/* Keep poking the Hypervisor until */
+	bne	2f			/* we're released */
+	/* Let the Hypervisor know we are alive */
+	/* 8002 is a call to HvCallCfg::getLps, a harmless Hypervisor function */
+	lis	r3,0x8002
+	rldicr	r3,r3,32,15		/* r0 = (r3 << 32) & 0xffff000000000000 */
+	li	r0,-1			/* r0=-1 indicates a Hypervisor call */
+	sc				/* Invoke the hypervisor via a system call */
+	b	1b
+#endif
+
+2:
+	HMT_LOW
 #ifdef CONFIG_SMP
 	lbz	r23,PACAPROCSTART(r13)	/* Test if this processor
 					 * should start */
@@ -91,7 +116,7 @@ iSeries_secondary_smp_loop:
 	li	r0,-1			/* r0=-1 indicates a Hypervisor call */
 	sc				/* Invoke the hypervisor via a system call */
 	mfspr	r13,SPRN_SPRG3		/* Put r13 back ???? */
-	b	1b			/* If SMP not configured, secondaries
+	b	2b			/* If SMP not configured, secondaries
 					 * loop forever */
 
 /***  ISeries-LPAR interrupt handlers ***/