[POWERPC] Add IRQSTACKS support on ppc32

This makes it possible to use separate stacks for hard and soft IRQs
on 32-bit powerpc as well as on 64-bit.  The code for 32-bit is just
the 32-bit analog of the 64-bit code.

* Added allocation and initialization of the irq stacks.  We limit the
  stacks to be in lowmem for ppc32.
* Implemented ppc32 versions of call_do_softirq() and call_handle_irq()
  to switch the stack pointers
* Reworked how we do stack overflow detection.  We now keep around the
  limit of the stack in the thread_struct and compare against the limit
  to see if we've overflowed.  We can now use this on ppc64 if desired.

[ paulus@samba.org: Fixed bug on 6xx where we need to reload r9 with the
  thread_info pointer. ]

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 84c868633068..0c8614d9875c 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -137,11 +137,12 @@ transfer_to_handler:
 2:      /* if from kernel, check interrupted DOZE/NAP mode and
          * check for stack overflow
          */
-        lwz     r9,THREAD_INFO-THREAD(r12)
-        cmplw   r1,r9                   /* if r1 <= current->thread_info */
+        lwz     r9,KSP_LIMIT(r12)
+        cmplw   r1,r9                   /* if r1 <= ksp_limit */
         ble-    stack_ovf               /* then the kernel stack overflowed */
 5:
 #ifdef CONFIG_6xx
+        rlwinm  r9,r1,0,0,31-THREAD_SHIFT
         tophys(r9,r9)                   /* check local flags */
         lwz     r12,TI_LOCAL_FLAGS(r9)
         mtcrf   0x01,r12