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, 48 insertions, 1 deletions

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index a5ae04a57c7..b7d140430a4 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -376,11 +376,28 @@ label##_common:						\
 	bl	hdlr;					\
 	b	.ret_from_except
 
+/*
+ * Like STD_EXCEPTION_COMMON, but for exceptions that can occur
+ * in the idle task and therefore need the special idle handling.
+ */
+#define STD_EXCEPTION_COMMON_IDLE(trap, label, hdlr)	\
+	.align	7;					\
+	.globl label##_common;				\
+label##_common:						\
+	EXCEPTION_PROLOG_COMMON(trap, PACA_EXGEN);	\
+	FINISH_NAP;					\
+	DISABLE_INTS;					\
+	bl	.save_nvgprs;				\
+	addi	r3,r1,STACK_FRAME_OVERHEAD;		\
+	bl	hdlr;					\
+	b	.ret_from_except
+
 #define STD_EXCEPTION_COMMON_LITE(trap, label, hdlr)	\
 	.align	7;					\
 	.globl label##_common;				\
 label##_common:						\
 	EXCEPTION_PROLOG_COMMON(trap, PACA_EXGEN);	\
+	FINISH_NAP;					\
 	DISABLE_INTS;					\
 	bl	.ppc64_runlatch_on;			\
 	addi	r3,r1,STACK_FRAME_OVERHEAD;		\
@@ -388,6 +405,25 @@ label##_common:						\
 	b	.ret_from_except_lite
 
 /*
+ * When the idle code in power4_idle puts the CPU into NAP mode,
+ * it has to do so in a loop, and relies on the external interrupt
+ * and decrementer interrupt entry code to get it out of the loop.
+ * It sets the _TLF_NAPPING bit in current_thread_info()->local_flags
+ * to signal that it is in the loop and needs help to get out.
+ */
+#ifdef CONFIG_PPC_970_NAP
+#define FINISH_NAP				\
+BEGIN_FTR_SECTION				\
+	clrrdi	r11,r1,THREAD_SHIFT;		\
+	ld	r9,TI_LOCAL_FLAGS(r11);		\
+	andi.	r10,r9,_TLF_NAPPING;		\
+	bnel	power4_fixup_nap;		\
+END_FTR_SECTION_IFSET(CPU_FTR_CAN_NAP)
+#else
+#define FINISH_NAP
+#endif
+
+/*
  * Start of pSeries system interrupt routines
  */
 	. = 0x100
@@ -772,6 +808,7 @@ hardware_interrupt_iSeries_masked:
 	.globl machine_check_common
 machine_check_common:
 	EXCEPTION_PROLOG_COMMON(0x200, PACA_EXMC)
+	FINISH_NAP
 	DISABLE_INTS
 	bl	.save_nvgprs
 	addi	r3,r1,STACK_FRAME_OVERHEAD
@@ -783,7 +820,7 @@ machine_check_common:
 	STD_EXCEPTION_COMMON(0xb00, trap_0b, .unknown_exception)
 	STD_EXCEPTION_COMMON(0xd00, single_step, .single_step_exception)
 	STD_EXCEPTION_COMMON(0xe00, trap_0e, .unknown_exception)
-	STD_EXCEPTION_COMMON(0xf00, performance_monitor, .performance_monitor_exception)
+	STD_EXCEPTION_COMMON_IDLE(0xf00, performance_monitor, .performance_monitor_exception)
 	STD_EXCEPTION_COMMON(0x1300, instruction_breakpoint, .instruction_breakpoint_exception)
 #ifdef CONFIG_ALTIVEC
 	STD_EXCEPTION_COMMON(0x1700, altivec_assist, .altivec_assist_exception)
@@ -1034,6 +1071,7 @@ unrecov_slb:
 	.globl hardware_interrupt_entry
 hardware_interrupt_common:
 	EXCEPTION_PROLOG_COMMON(0x500, PACA_EXGEN)
+	FINISH_NAP
 hardware_interrupt_entry:
 	DISABLE_INTS
 	bl	.ppc64_runlatch_on
@@ -1041,6 +1079,15 @@ hardware_interrupt_entry:
 	bl	.do_IRQ
 	b	.ret_from_except_lite
 
+#ifdef CONFIG_PPC_970_NAP
+power4_fixup_nap:
+	andc	r9,r9,r10
+	std	r9,TI_LOCAL_FLAGS(r11)
+	ld	r10,_LINK(r1)		/* make idle task do the */
+	std	r10,_NIP(r1)		/* equivalent of a blr */
+	blr
+#endif
+
 	.align	7
 	.globl alignment_common
 alignment_common: