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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 EFF98C2BA83 for ; Fri, 7 Feb 2020 16:05:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C11FE214AF for ; Fri, 7 Feb 2020 16:05:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727123AbgBGQF0 (ORCPT ); Fri, 7 Feb 2020 11:05:26 -0500 Received: from foss.arm.com ([217.140.110.172]:41630 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726874AbgBGQFZ (ORCPT ); Fri, 7 Feb 2020 11:05:25 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id EDECE1FB; Fri, 7 Feb 2020 08:05:24 -0800 (PST) Received: from bogus (e103737-lin.cambridge.arm.com [10.1.197.49]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id BD1DA3F68E; Fri, 7 Feb 2020 08:05:22 -0800 (PST) Date: Fri, 7 Feb 2020 16:05:13 +0000 From: Sudeep Holla To: Ulf Hansson Cc: Lina Iyer , Maulik Shah , Stephen Boyd , Andy Gross , David Brown , Lorenzo Pieralisi , linux-arm-msm , Linux Kernel Mailing List , Linux PM , Linux ARM , Bjorn Andersson , Evan Green , Doug Anderson , Rajendra Nayak , lsrao@codeaurora.org, "Rafael J. Wysocki" , Sudeep Holla Subject: Re: [PATCH v3 5/7] drivers: firmware: psci: Add hierarchical domain idle states converter Message-ID: <20200207160504.GA8342@bogus> References: <0d7f7ade-3a1e-5428-d851-f1a886f58712@codeaurora.org> <20200204152132.GA44858@bogus> <6ff7c82d-4204-a339-4070-0154ab4515f1@codeaurora.org> <20200205140603.GB38466@bogus> <20200205161816.GD38466@bogus> <20200206204514.GB8107@codeaurora.org> <20200207111955.GA40103@bogus> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 07, 2020 at 01:32:28PM +0100, Ulf Hansson wrote: > [...] > > > > I understand the arguments for using PC vs OSI and agree with it. But > > > what in PSCI is against Linux knowing when the last core is powering > > > down when the PSCI is configured to do only Platform Cordinated. > > > > Nothing :D. But knowing the evolution and reasons for adding OSI in the > > PSCI specification and having argued about benefits of OSI over PC for > > years and finally when we have it in mainline, this argument of using > > PC for exact reasons why OSI evolved is something I can't understand > > and I am confused. > > > > > There should not be any objection to drivers knowing when all the cores > > > are powered down, be it reference counting CPU PM notifications or using > > > a cleaner approach like this where GendPD framwork does everything > > > cleanly and gives a nice callback. ARM architecture allows for different > > > aspects of CPU access be handled at different levels. I see this as an > > > extension of that approach. > > > > > > > One thing that was repeatedly pointed out during OSI patch review was no > > extra overhead for PC mode where firmware can make decisions. So, just > > use OSI now and let us be done with this discussion of OSI vs PC. If PC > > is what you think you need for future, we can revert all OSI changes and > > start discussing again :-) > > Just to make it clear, I fully agree with you in regards to overhead > for PC-mode. This is especially critical for ARM SoCs with lots of > cores, I assume. > > However, the overhead you refer to, is *only* going to be present in > case when the DTS has the hierarchical CPU topology description with > "power-domains". Because, that is *optional* to use, I am expecting > only those SoC/platforms that needs to manage last-man activities to > use this layout, the others will remain unaffected. > > That said, does that address your concern? > I have already expressed my view and concerns in response to Lina and Bjorn's emails. -- Regards, Sudeep