powerpc/pmac/smp: Properly NAP offlined CPU on G5

The current code soft-disables, and then goes to NAP mode which
turns interrupts on. That means that if an interrupt occurs, we
will hit the masked interrupt code path which isn't what we want,
as it will return with EE off, which will either get us out of
NAP mode, or fail to enter it (according to spec).

Instead, let's just rely on the fact that it is safe to take
decrementer interrupts on an offline CPU and leave interrupts
enabled. We can also get rid of the special case in asm for
power4_cpu_offline_powersave() and just use power4_idle().

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 782f23df7c85..271140b38b6f 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -536,6 +536,13 @@ _GLOBAL(pmac_secondary_start)
         add     r13,r13,r4              /* for this processor.          */
         mtspr   SPRN_SPRG_PACA,r13      /* Save vaddr of paca in an SPRG*/
 
+        /* Mark interrupts soft and hard disabled (they might be enabled
+         * in the PACA when doing hotplug)
+         */
+        li      r0,0
+        stb     r0,PACASOFTIRQEN(r13)
+        stb     r0,PACAHARDIRQEN(r13)
+
         /* Create a temp kernel stack for use before relocation is on.  */
         ld      r1,PACAEMERGSP(r13)
         subi    r1,r1,STACK_FRAME_OVERHEAD