Subject: [PATCH 10/14] powerpc/64: CTRL[RUN] run-latch setting optimisation

From: Nicholas Piggin <[email-masked]>
Date: Fri, 2 Jun 2017 17:39:42 +1000

The CTRL register is read-only except bit 63 which is the run
latch control. This means it can be updated with a mtspr rather
than mfspr/mtspr.

Signed-off-by: Nicholas Piggin <[email-masked]>
---
 arch/powerpc/kernel/process.c | 12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 5cbb8b1faf7e..633ec9967141 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1964,12 +1964,8 @@ void show_stack(struct task_struct *tsk, unsigned long *stack)
 void notrace __ppc64_runlatch_on(void)
 {
 	struct thread_info *ti = current_thread_info();
-	unsigned long ctrl;
-
-	ctrl = mfspr(SPRN_CTRLF);
-	ctrl |= CTRL_RUNLATCH;
-	mtspr(SPRN_CTRLT, ctrl);
 
+	mtspr(SPRN_CTRLT, CTRL_RUNLATCH);
 	ti->local_flags |= _TLF_RUNLATCH;
 }
 
@@ -1977,13 +1973,9 @@ void notrace __ppc64_runlatch_on(void)
 void notrace __ppc64_runlatch_off(void)
 {
 	struct thread_info *ti = current_thread_info();
-	unsigned long ctrl;
 
 	ti->local_flags &= ~_TLF_RUNLATCH;
-
-	ctrl = mfspr(SPRN_CTRLF);
-	ctrl &= ~CTRL_RUNLATCH;
-	mtspr(SPRN_CTRLT, ctrl);
+	mtspr(SPRN_CTRLT, 0);
 }
 #endif /* CONFIG_PPC64 */
 
-- 
2.11.0