linux-kernel - [PATCH] powerpc/powernv: Clear LPCR[PECE1] via stop-api only for deep state offline

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Date:   Thu, 31 Aug 2017 17:17:41 +0530
From:   "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
        Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com>,
        Pavithra Prakash <pavirampu@...ux.vnet.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
Subject: [PATCH] powerpc/powernv: Clear LPCR[PECE1] via stop-api only for deep state offline

From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>

commit 24be85a23d1f ("powerpc/powernv: Clear PECE1 in LPCR via
stop-api only on Hotplug") clears the PECE1 bit of the LPCR via
stop-api during CPU-Hotplug to prevent wakeup due to a decrementer on
an offlined CPU which is in a deep stop state.

In the case where the stop-api support is found to be lacking, the
commit 785a12afdb4a ("powerpc/powernv/idle: Disable LOSE_FULL_CONTEXT
states when stop-api fails") disables deep states that lose hypervisor
context. Thus in this case, the offlined CPU will be put to some
shallow idle state.

However, we currently unconditionally clear the PECE1 in LPCR via
stop-api during CPU-Hotplug even when deep states are disabled due to
stop-api failure.

Fix this by clearing PECE1 of LPCR via stop-api during CPU-Hotplug
*only* when the offlined CPU will be put to a deep state that loses
hypervisor context.

Fixes: commit 24be85a23d1f ("powerpc/powernv: Clear PECE1 in LPCR via
stop-api only on Hotplug")

Reported-by: Pavithra Prakash <pavirampu@...ux.vnet.ibm.com>
Signed-off-by: Gautham R. Shenoy <ego@...ux.vnet.ibm.com>
---
 arch/powerpc/platforms/powernv/idle.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
index 9f59041..23f8fba 100644
--- a/arch/powerpc/platforms/powernv/idle.c
+++ b/arch/powerpc/platforms/powernv/idle.c
@@ -393,7 +393,13 @@ static void pnv_program_cpu_hotplug_lpcr(unsigned int cpu, u64 lpcr_val)
 	u64 pir = get_hard_smp_processor_id(cpu);

 	mtspr(SPRN_LPCR, lpcr_val);
-	opal_slw_set_reg(pir, SPRN_LPCR, lpcr_val);
+
+	/*
+	 * Program the LPCR via stop-api only for deepest stop state
+	 * can lose hypervisor context.
+	 */
+	if (supported_cpuidle_states & OPAL_PM_LOSE_FULL_CONTEXT)
+		opal_slw_set_reg(pir, SPRN_LPCR, lpcr_val);
 }

 /*
-- 
1.9.4