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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham 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 8B7EAC48BE3 for ; Thu, 20 Jun 2019 16:34:41 +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 651462085A for ; Thu, 20 Jun 2019 16:34:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="kB/9rFgU" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 651462085A 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=T6kiQuq5w41KCIrNnqLDmhkaAR/nK0hUttBlxPdUgxY=; b=kB/9rFgUExRgzI KxiiDZzH1c0c9KPolSBGmQB5eT1zlynoXwKmtgQODRxE1ScJUmZL79ax+drUiDbfdToR3LSRNnWQp zm0QY/kv/jwvS79rEj51GL3FRbS4A6+kC+AcffpFEbi+jv1hoUMVrqgo/TTx4OJjHhYzACtAGjuRH zHnxojr9UZ2Y0qxtIQJxKLYPWXpg9+3QfoMSQRW6gc2VnPCTCQWTiIpPBF5lQ3WV3kJjw2iHpS7dY 1IWSYyACQquHa5dQg1OF7dbvLDjDy2vPRRjbLii2+eSYPUZqWPPhPBtW0xN4EbqJ92DyCMbXKkajJ +RBbUU4JX3ES6zdLq9yQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1he01D-00038k-Hu; Thu, 20 Jun 2019 16:34:35 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1he01A-00038F-V0 for linux-arm-kernel@lists.infradead.org; Thu, 20 Jun 2019 16:34:34 +0000 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 C4E8A2B; Thu, 20 Jun 2019 09:34:29 -0700 (PDT) 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 A5E2B3F246; Thu, 20 Jun 2019 09:34:28 -0700 (PDT) Date: Thu, 20 Jun 2019 17:34:26 +0100 From: Sudeep Holla To: Mathieu Poirier Subject: Re: [PATCH v1 5/5] coresight: etm4x: save/restore state across CPU low power states Message-ID: <20190620163426.GC25273@e107155-lin> References: <20190618125433.9739-1-andrew.murray@arm.com> <20190618125433.9739-6-andrew.murray@arm.com> <20190618132159.GA18121@e107155-lin> <15ef45d4-ee1a-3c45-878d-f08f0a84cfeb@arm.com> <20190619110749.GD1360@e107155-lin> <20190620114116.GE20984@e119886-lin.cambridge.arm.com> <20190620154154.GB25273@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-20190620_093433_047664_D5099138 X-CRM114-Status: GOOD ( 16.02 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Al Grant , Suzuki K Poulose , Alexander Shishkin , Sudeep Holla , Andrew Murray , linux-arm-kernel , Mike Leach 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 Thu, Jun 20, 2019 at 10:14:04AM -0600, Mathieu Poirier wrote: > On Thu, 20 Jun 2019 at 09:41, Sudeep Holla wrote: > > [...] > > Sorry but even then I prefer it not to be default and force extra work > > to the people who add support and constantly be reminded that it's > > broken and they are deviating from default behaviour in the kernel > > which may come and latency penalty. > > > > Making it default may hide the problem if Linux is used for some validation. > > > > Also we hardly have 3-4 platforms in upstream that support coresight, > > and many are broken except Juno. But that doesn't imply all others > > are broken and we just can't derive that unless we have more information. > > For now we have a clear trend. To me it is not a matter of broken vs. > non-broken but more about what people want to do or can > (realistically) do. > No disagreement there. > The coresight specification is broad and very permissive in terms of > implementation defined choices. It is not because the TRCPDCR.PU it > not taken into account by a platform that it is automatically broken. > This could be a design choice or a trade off. We already have two > ways of putting a CPU to sleep (architected or OS driven), we simply > do the same here for coresight. > Sure, if the term "broken" is inappropriate I am fine if anything else is used. The point is we are adding an idle notifier that adds latency and must be done if and only if necessary. How you identify that and implement doesn't bother me much, making that default just based on the fact that more platforms need it compared to others definitely does. So I am fine if this needs to be advertised *not broken* but *by design*, sure go for it. My main concern was additional latency that this introduces for platforms that don't require. -- Regards, Sudeep _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel