powerpc/perf: POWER9 PMU stops after idle workaround

POWER9 DD2 PMU can stop after a state-loss idle in some conditions.

A solution is to set then clear MMCRA[60] after wake from state-loss
idle. MMCRA[60] is a non-architected bit, see the user manual for
details.
Signed-off-by: NNicholas Piggin <npiggin@gmail.com>
Acked-by: NMadhavan Srinivasan <maddy@linux.vnet.ibm.com>
Reviewed-by: NVaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Acked-by: NAnton Blanchard <anton@samba.org>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/idle_book3s.S

@@ -460,11 +460,17 @@ pnv_restore_hyp_resource_arch300:
 	/*
 	 * Workaround for POWER9, if we lost resources, the ERAT
 	 * might have been mixed up and needs flushing. We also need
-	 * to reload MMCR0 (see comment above).
+	 * to reload MMCR0 (see comment above). We also need to set
+	 * then clear bit 60 in MMCRA to ensure the PMU starts running.
 	 */
 	blt	cr3,1f
 	PPC_INVALIDATE_ERAT
 	ld	r1,PACAR1(r13)
+	mfspr	r4,SPRN_MMCRA
+	ori	r4,r4,(1 << (63-60))
+	mtspr	SPRN_MMCRA,r4
+	xori	r4,r4,(1 << (63-60))
+	mtspr	SPRN_MMCRA,r4
 	ld	r4,_MMCR0(r1)
 	mtspr	SPRN_MMCR0,r4
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