From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9EFA3FA3729 for ; Mon, 21 Jan 2019 11:23:14 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 6F43C20663 for ; Mon, 21 Jan 2019 11:23:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="eL1ocrmY" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6F43C20663 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=t9WnZyrbq+XiaYaEFDV4RjEMFb+QWLhb327ckeS1L2M=; b=eL1ocrmYH0nEo1 SBxnSr+zbupRE638Ws7nAyOXZBqKE6IsufomU2H00O2dmSx7VxKybyXlCY6oxAfNVeCobiQGsgqVH 67DNcmWiQxuz00ZP+u0UWG0Hq3SLR/pZtZ4FnZzBjN95OzmjOwt/xlc0cBfKP5eVAo+mPYrih0fam YA8rZRa1TQy72j8uGFGmz9Q90ntdJA9uyIFxrHIrrwCwCdkZdfjvylaRD0lA0Eax+aJLdu+Qo1Waa TbGGpq54xSGpMs9aCurmXoA6qgReFd+2YPkdCOLgPAX68vjwATP/sslWKvdO1tufLNmDc7dzSZT/l d2wp/WOPfxxWlgyWYBkw==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1glXfT-0000zO-EA; Mon, 21 Jan 2019 11:23:03 +0000 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70] helo=foss.arm.com) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1glXfQ-0000z0-75 for linux-arm-kernel@lists.infradead.org; Mon, 21 Jan 2019 11:23:01 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id EFAA6EBD; Mon, 21 Jan 2019 03:22:57 -0800 (PST) Received: from e107155-lin (e107155-lin.cambridge.arm.com [10.1.196.42]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B7EEE3F5C1; Mon, 21 Jan 2019 03:22:55 -0800 (PST) Date: Mon, 21 Jan 2019 11:22:48 +0000 From: Sudeep Holla To: Pramod Kumar Subject: Re: [PATCH RFC 1/1] arm64: Use PSCI calls for CPU stop when hotplug is supported Message-ID: <20190121112248.GA27784@e107155-lin> References: <1547790380-6276-1-git-send-email-pramod.kumar@broadcom.com> <20190118113242.GA8928@e107155-lin> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190121_032300_260277_3DC8341A X-CRM114-Status: GOOD ( 23.18 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Rob Herring , Lorenzo Pieralisi , Suzuki K Poulose , Catalin Marinas , Steve Capper , Will Deacon , linux-kernel@vger.kernel.org, BCM Kernel Feedback , Sudeep Holla , Dave Martin , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Jan 21, 2019 at 11:28:27AM +0530, Pramod Kumar wrote: > On Fri, Jan 18, 2019 at 5:02 PM Sudeep Holla wrote: > > On Fri, Jan 18, 2019 at 11:16:20AM +0530, Pramod Kumar wrote: > > > If CPU hotplug is supported, ipi_cpu_stop should use PSCI cpudie > > > call to stop the CPU. This call ensures L1/L2 cache flush, > > > CPUs cache-cohenrecy setting w.r.to interconnect. > > > > Firstly, this is not specific to PSCI and I don't see any PSCI calls as > > $subject claims. > > I had seen all the other cpu ops methods where only PSCI supports only > cpu_die features hence used PSCI reference in my subject line to be more > clear where this die gets converted in last. > OK, but since you are not directly dealing with PSCI APIs, it's misleading. > > Next, you fail to explain why do you have to ensure > > caches are cleaned and why do you need that in ipi_cpu_stop ? > > What's the use case ? > > > Need comes from a specific use case where one Accelerator card(SoC) is > plugged in a sever over a PCIe interface. This Card gets supply from a > battery, which could provide very less power for a very small time, in case > of any power loss. Once Card switches to battery, this has to reduce its > power consumption to its lowest point and back-up the DDR contents asap > before battery gets fully drained off. > OK, but I was expecting the complete call path for this use-case. > Since battery can provide limited power for a very short time hence need to > transition to lowest power. As per the transition process , CPUs power > domain has to be off but before that it needs to flush out its content to > system memory(L3) so that content could be backed-up by a MCU, a controller > consuming very less power. Since we can not afford plugging-out every > individual CPUs in sequence hence uses ipi_cpu_stop for all other CPUs So, you are randomly using ipi_cpu_stop for something it's not supposed to be used. What do you exactly want to achieve in that context where you need to save power ? Why system off or reset not sufficient ? -- Regards, Sudeep _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel