From patchwork Fri Sep 27 14:29:13 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Lorenzo Pieralisi X-Patchwork-Id: 2955391 Return-Path: X-Original-To: patchwork-linux-arm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.19.201]) by patchwork1.web.kernel.org (Postfix) with ESMTP id A0C799F288 for ; Fri, 27 Sep 2013 14:30:02 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 32BCE202A1 for ; Fri, 27 Sep 2013 14:30:01 +0000 (UTC) Received: from casper.infradead.org (casper.infradead.org [85.118.1.10]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id AAD9C20295 for ; Fri, 27 Sep 2013 14:29:59 +0000 (UTC) Received: from merlin.infradead.org ([2001:4978:20e::2]) by casper.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1VPZ3I-0005K4-64; Fri, 27 Sep 2013 14:29:52 +0000 Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1VPZ3F-0006UD-HO; Fri, 27 Sep 2013 14:29:49 +0000 Received: from service87.mimecast.com ([91.220.42.44]) by merlin.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1VPZ3B-0006Ta-Tq for linux-arm-kernel@lists.infradead.org; Fri, 27 Sep 2013 14:29:47 +0000 Received: from cam-owa2.Emea.Arm.com (fw-tnat.cambridge.arm.com [217.140.96.21]) by service87.mimecast.com; Fri, 27 Sep 2013 15:29:21 +0100 Received: from e102568-lin.cambridge.arm.com ([10.1.255.212]) by cam-owa2.Emea.Arm.com with Microsoft SMTPSVC(6.0.3790.3959); Fri, 27 Sep 2013 15:29:18 +0100 From: Lorenzo Pieralisi To: linux-arm-kernel@lists.infradead.org, linux-pm@vger.kernel.org Subject: [PATCH] arm: vexpress: tc2: fix CPU hotplug and CPU idle race on cluster power down Date: Fri, 27 Sep 2013 15:29:13 +0100 Message-Id: <1380292153-10480-1-git-send-email-lorenzo.pieralisi@arm.com> X-Mailer: git-send-email 1.8.2.2 X-OriginalArrivalTime: 27 Sep 2013 14:29:18.0609 (UTC) FILETIME=[F33EE010:01CEBB8D] X-MC-Unique: 113092715292101201 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20130927_102946_154535_08630304 X-CRM114-Status: GOOD ( 14.35 ) X-Spam-Score: -2.6 (--) Cc: Nicolas Pitre , Lorenzo Pieralisi , Sudeep KarkadaNagesha , Kevin Hilman , Olof Johansson , Dave Martin X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Spam-Status: No, score=-6.6 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_MED, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On the TC2 testchip, when all CPUs in a cluster enter standbywfi and commit a power down request, the power controller will wait for standbywfil2 coming from L2 cache controller to shut the cluster down. By the time all CPUs in a cluster commit a power down request and enter wfi, the power controller cannot backtrack, or put it another way, a CPU must not be allowed to complete execution independently of the power controller, the only way for it to resume properly must be upon wake-up IRQ pending and subsequent reset triggered from the power controller. Current MCPM back-end for TC2 disables the GIC CPU IF only when power down is committed through the suspend method, that makes sense since a suspended CPU is still online and can receive interrupts whereas a hotplugged CPU, since it is offline, migrated all IRQs and shutdown the per-CPU peripherals, hence their PPIs. The flaw with this reasoning is the following. If all CPUs in a clusters are entering a power down state either through CPU idle or CPU hotplug, when the last man successfully completes the MCPM power down sequence (and executes wfi), power controller waits for L2 wfi signal to quiesce the cluster and shut it down. If, when all CPUs are sitting in wfi, an online CPU hotplugs back in one of the CPUs in the cluster being shutdown, that CPU receives an IPI that causes wfi to complete (since MCPM power down method does not disable the GIC CPU IF in that case - CPU being hotplugged out, not idle) and the power controller will never see the stanbywfil2 signal coming from L2 that is required for shutdown to happen and the system deadlocks. The only solution to this problem consists in disabling the GIC CPU IF on a CPU committed to power down regardless of the power down entry method (CPU hotplug or CPU idle). This way, CPU wake-up is under power controller control, which prevents unexpected wfi exit caused by a pending IRQ. This patch moves the GIC CPU IF disable call in the TC2 MCPM implementation from the suspend method to the power down method to fix the mentioned race condition. Signed-off-by: Lorenzo Pieralisi Signed-off-by: Sudeep KarkadaNagesha Reviewed-by: Dave Martin Tested-by: Dave Martn (for kexec) --- arch/arm/mach-vexpress/tc2_pm.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/arch/arm/mach-vexpress/tc2_pm.c b/arch/arm/mach-vexpress/tc2_pm.c index 7aeb5d6..e6eb481 100644 --- a/arch/arm/mach-vexpress/tc2_pm.c +++ b/arch/arm/mach-vexpress/tc2_pm.c @@ -131,6 +131,16 @@ static void tc2_pm_down(u64 residency) } else BUG(); + /* + * If the CPU is committed to power down, make sure + * the power controller will be in charge of waking it + * up upon IRQ, ie IRQ lines are cut from GIC CPU IF + * to the CPU by disabling the GIC CPU IF to prevent wfi + * from completing execution behind power controller back + */ + if (!skip_wfi) + gic_cpu_if_down(); + if (last_man && __mcpm_outbound_enter_critical(cpu, cluster)) { arch_spin_unlock(&tc2_pm_lock); @@ -231,7 +241,6 @@ static void tc2_pm_suspend(u64 residency) cpu = MPIDR_AFFINITY_LEVEL(mpidr, 0); cluster = MPIDR_AFFINITY_LEVEL(mpidr, 1); ve_spc_set_resume_addr(cluster, cpu, virt_to_phys(mcpm_entry_point)); - gic_cpu_if_down(); tc2_pm_down(residency); }