From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-x243.google.com (mail-pf0-x243.google.com [IPv6:2607:f8b0:400e:c00::243]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3xkG1n2HkWzDqjS for ; Fri, 1 Sep 2017 20:38:53 +1000 (AEST) Received: by mail-pf0-x243.google.com with SMTP id k3so1438931pfc.3 for ; Fri, 01 Sep 2017 03:38:53 -0700 (PDT) Date: Fri, 1 Sep 2017 20:38:37 +1000 From: Nicholas Piggin To: Akshay Adiga Cc: linux-kernel@vger.kernel.org, Shilpasri G Bhat , Pavithra Prakash , linuxppc-dev@lists.ozlabs.org, "Gautham R. Shenoy" Subject: Re: [PATCH] powerpc/powernv: Clear LPCR[PECE1] via stop-api only for deep state offline Message-ID: <20170901203837.765f1875@roar.ozlabs.ibm.com> In-Reply-To: References: <1504180061-32345-1-git-send-email-ego@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Fri, 1 Sep 2017 15:38:59 +0530 Akshay Adiga wrote: > On 08/31/2017 05:37 PM, Nicholas Piggin wrote: > > On Thu, 31 Aug 2017 17:17:41 +0530 > > "Gautham R. Shenoy" wrote: > > > > > From: "Gautham R. Shenoy" > > > > > > 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. > > > > This looks okay to me. The bug is due to calling opal_slw_set_reg when > > firmware has not enabled that feature, right? > Yes, > > 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. > > If a shallow state ( < stop4 ) is being chosen for cpu hotplug, then : > 1) this opal call is not required. > 2) may not be supported. > > Hence should call opal_slw_set_reg() only if a deep state chosen for > cpu hotplug. That makes sense, thanks for confirming. > > > > > > > > Fixes: commit 24be85a23d1f ("powerpc/powernv: Clear PECE1 in LPCR via > > > stop-api only on Hotplug") > > > > > > Reported-by: Pavithra Prakash > > > Signed-off-by: Gautham R. Shenoy Reviewed-by: Nicholas Piggin > > > --- > > > 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); > > > } > > > > > > /* > > >