[Zesty][PATCH 1/1] powerpc/perf: Avoid spurious PMU interrupts after idle

[Rodrigo R. Galvao]

From: Nicholas Piggin <npiggin at gmail.com>

BugLink: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1709352

POWER9 DD2 can see spurious PMU interrupts after state-loss idle in
some conditions.

A solution is to save and reload MMCR0 over state-loss idle.

Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
Acked-by: Madhavan Srinivasan <maddy at linux.vnet.ibm.com>
Tested-by: Anton Blanchard <anton at samba.org>
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
(cherry picked from commit 101dd590a7fa37954540cf3149a1c502c0acc524)
Signed-off-by: Rodrigo R. Galvao <rosattig at linux.vnet.ibm.com>
---
 arch/powerpc/kernel/idle_book3s.S | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S
index fb762ee..e003fb9 100644
--- a/arch/powerpc/kernel/idle_book3s.S
+++ b/arch/powerpc/kernel/idle_book3s.S
@@ -29,6 +29,7 @@
  * Use unused space in the interrupt stack to save and restore
  * registers for winkle support.
  */
+#define _MMCR0	GPR0
 #define _SDR1	GPR3
 #define _RPR	GPR4
 #define _SPURR	GPR5
@@ -282,6 +283,14 @@ power_enter_stop:
 	b 	pnv_wakeup_noloss
 
 .Lhandle_esl_ec_set:
+	/*
+	 * POWER9 DD2 can incorrectly set PMAO when waking up after a
+	 * state-loss idle. Saving and restoring MMCR0 over idle is a
+	 * workaround.
+	 */
+	mfspr	r4,SPRN_MMCR0
+	std	r4,_MMCR0(r1)
+
 /*
  * Check if the requested state is a deep idle state.
  */
@@ -434,10 +443,14 @@ FTR_SECTION_ELSE_NESTED(70)
 ALT_FTR_SECTION_END_NESTED_IFSET(CPU_FTR_POWER9_DD1, 70)
 	/*
 	 * Workaround for POWER9, if we lost resources, the ERAT
-	 * might have been mixed up and needs flushing.
+	 * might have been mixed up and needs flushing. We also need
+	 * to reload MMCR0 (see comment above).
 	 */
 	blt	cr3,1f
 	PPC_INVALIDATE_ERAT
+	ld	r1,PACAR1(r13)
+	ld	r4,_MMCR0(r1)
+	mtspr	SPRN_MMCR0,r4
 1:
 	/*
 	 * POWER ISA 3. Use PSSCR to determine if we
-- 
2.7.4