powerpc/8xx: use SPRN_EIE and SPRN_EID to enable/disable interrupts

The 8xx has two special registers called EID (External Interrupt
Disable) and EIE (External Interrupt Enable) for clearing/setting
EE in MSR. It avoids the three instructions set mfmsr/ori/mtmsr or
mfmsr/rlwinm/mtmsr and it avoids using a general register.

We just have to write something in the special register to change MSR EE
bit. So we write r0 into the register, regardless of r0 value.

Writing to one of those two special registers also set the MSR RI bit,
but this bit is only unset during beginning of exception prolog and end
of exception epilog. When executing C-functions MSR RI is always set.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Scott Wood <oss@buserror.net>

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index 9dddabc..b320c8f 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -1249,6 +1249,8 @@ static inline void mtmsr_isync(unsigned long val)
 				     : "r" ((unsigned long)(v)) \
 				     : "memory")
 #endif
+#define wrtspr(rn)	asm volatile("mtspr " __stringify(rn) ",0" : \
+				     : : "memory")
 
 extern void msr_check_and_set(unsigned long bits);
 extern bool strict_msr_control;