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