powerpc: Use correct sequence for putting CPU into nap mode

We weren't using the recommended sequence for putting the CPU into
nap mode.  When I changed the idle loop, for some reason 7447A cpus
started hanging when we put them into nap mode.  Changing to the
recommended sequence fixes that.

The complexity here is that the recommended sequence is a loop that
keeps putting the cpu back into nap mode.  Clearly we need some way
to break out of the loop when an interrupt (external interrupt,
decrementer, performance monitor) occurs.  Here we use a bit in
the thread_info struct to indicate that we need this, and the exception
entry code notices this and arranges for the exception to return
to the value in the link register, thus breaking out of the loop.
We use a new `local_flags' field in the thread_info which we can
alter without needing to use an atomic update sequence.

The PPC970 has the same recommended sequence, so we do the same thing
there too.

This also fixes a bug in the kernel stack overflow handling code on
32-bit, since it was causing a value that we needed in a register to
get trashed.

Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 17 insertions, 18 deletions

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index b3a979467225..8866fd26c6b9 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -128,37 +128,36 @@ transfer_to_handler:
         stw     r12,4(r11)
 #endif
         b       3f
+
 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 */
+        ble-    stack_ovf               /* then the kernel stack overflowed */
+5:
 #ifdef CONFIG_6xx
-        mfspr   r11,SPRN_HID0
-        mtcr    r11
-BEGIN_FTR_SECTION
-        bt-     8,4f                    /* Check DOZE */
-END_FTR_SECTION_IFSET(CPU_FTR_CAN_DOZE)
-BEGIN_FTR_SECTION
-        bt-     9,4f                    /* Check NAP */
-END_FTR_SECTION_IFSET(CPU_FTR_CAN_NAP)
+        tophys(r9,r9)                   /* check local flags */
+        lwz     r12,TI_LOCAL_FLAGS(r9)
+        mtcrf   0x01,r12
+        bt-     31-TLF_NAPPING,4f
 #endif /* CONFIG_6xx */
         .globl transfer_to_handler_cont
 transfer_to_handler_cont:
-        lwz     r11,THREAD_INFO-THREAD(r12)
-        cmplw   r1,r11                  /* if r1 <= current->thread_info */
-        ble-    stack_ovf               /* then the kernel stack overflowed */
 3:
         mflr    r9
         lwz     r11,0(r9)               /* virtual address of handler */
         lwz     r9,4(r9)                /* where to go when done */
-        FIX_SRR1(r10,r12)
         mtspr   SPRN_SRR0,r11
         mtspr   SPRN_SRR1,r10
         mtlr    r9
         SYNC
         RFI                             /* jump to handler, enable MMU */
 
-#ifdef CONFIG_6xx       
-4:      b       power_save_6xx_restore
+#ifdef CONFIG_6xx
+4:      rlwinm  r12,r12,0,~_TLF_NAPPING
+        stw     r12,TI_LOCAL_FLAGS(r9)
+        b       power_save_6xx_restore
 #endif
 
 /*
@@ -167,10 +166,10 @@ transfer_to_handler_cont:
  */
 stack_ovf:
         /* sometimes we use a statically-allocated stack, which is OK. */
-        lis     r11,_end@h
-        ori     r11,r11,_end@l
-        cmplw   r1,r11
-        ble     3b                      /* r1 <= &_end is OK */
+        lis     r12,_end@h
+        ori     r12,r12,_end@l
+        cmplw   r1,r12
+        ble     5b                      /* r1 <= &_end is OK */
         SAVE_NVGPRS(r11)
         addi    r3,r1,STACK_FRAME_OVERHEAD
         lis     r1,init_thread_union@ha