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>
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 2cdc35c..65f67f9 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -366,6 +366,7 @@
select U3_DART
select MPIC_BROKEN_U3
select GENERIC_TBSYNC
+ select PPC_970_NAP
default y
config PPC_PREP
@@ -383,6 +384,7 @@
select MPIC_BROKEN_U3
select GENERIC_TBSYNC
select PPC_UDBG_16550
+ select PPC_970_NAP
default n
help
This option enables support for the Maple 970FX Evaluation Board.
@@ -457,6 +459,10 @@
bool
default n
+config PPC_970_NAP
+ bool
+ default n
+
source "drivers/cpufreq/Kconfig"
config CPU_FREQ_PMAC