Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751898AbdIAKJM (ORCPT ); Fri, 1 Sep 2017 06:09:12 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:55686 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751687AbdIAKJK (ORCPT ); Fri, 1 Sep 2017 06:09:10 -0400 From: Akshay Adiga To: Nicholas Piggin Subject: Re: [PATCH] powerpc/powernv: Clear LPCR[PECE1] via stop-api only for deep state offline References: <1504180061-32345-1-git-send-email-ego@linux.vnet.ibm.com> <> Cc: linux-kernel@vger.kernel.org, Shilpasri G Bhat , Pavithra Prakash , linuxppc-dev@lists.ozlabs.org, "Gautham R. Shenoy" Date: Fri, 1 Sep 2017 15:38:59 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable x-cbid: 17090110-0012-0000-0000-0000025AD2BE X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17090110-0013-0000-0000-00000776A911 Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-09-01_03:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1709010146 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2882 Lines: 75 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. > > > > > 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 > > --- > > 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); > > } > > > > /* >