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, 6 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/hw_irq.h b/arch/powerpc/include/asm/hw_irq.h
index c7d82ff62a33..eba60416536e 100644
--- a/arch/powerpc/include/asm/hw_irq.h
+++ b/arch/powerpc/include/asm/hw_irq.h
@@ -155,6 +155,8 @@ static inline unsigned long arch_local_irq_save(void)
 	unsigned long flags = arch_local_save_flags();
 #ifdef CONFIG_BOOKE
 	asm volatile("wrteei 0" : : : "memory");
+#elif defined(CONFIG_PPC_8xx)
+	wrtspr(SPRN_EID);
 #else
 	SET_MSR_EE(flags & ~MSR_EE);
 #endif
@@ -165,6 +167,8 @@ static inline void arch_local_irq_disable(void)
 {
 #ifdef CONFIG_BOOKE
 	asm volatile("wrteei 0" : : : "memory");
+#elif defined(CONFIG_PPC_8xx)
+	wrtspr(SPRN_EID);
 #else
 	arch_local_irq_save();
 #endif
@@ -174,6 +178,8 @@ static inline void arch_local_irq_enable(void)
 {
 #ifdef CONFIG_BOOKE
 	asm volatile("wrteei 1" : : : "memory");
+#elif defined(CONFIG_PPC_8xx)
+	wrtspr(SPRN_EIE);
 #else
 	unsigned long msr = mfmsr();
 	SET_MSR_EE(msr | MSR_EE);