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=-8.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 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 95AE8C31E40 for ; Tue, 15 Sep 2020 23:02:04 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 52B87206DC for ; Tue, 15 Sep 2020 23:02:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="g/ojOu5m" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 52B87206DC Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+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=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:Mime-Version:References:In-Reply-To:Date:To:From: Subject:Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=qz3Q9J1bLZpRGiZNKfDSjvLKx5tnaah5VoGlCFH4/a8=; b=g/ojOu5mS45NsbAzjYD+paTPA Z0obzARguETrBlUmbZj/tIzCnCoJlxwiC1eCtO1JuKnzlrjPc0aeUCas150zDB/aUQtGBtpAS1Arg /6XowpvpUsAEc25SmbVacERBc2RMDfz+6ctpfy+RsDip6OvbQ5Sf6rdF+xm/yMcNMtEE/XhoV+bif dJV+SvSr0bDUtxdibWv/9XO7v8T+d+VLEzeZrm6Jypm/DT+/s5eDndZ/GfUH3PPGRuIi+q0YpeuZj XBI7BJQpUudqzcn45novusrEK9lDj70FLA657EhquRU3uIz88DW3aGGtPkJ3n+ee/jX04A0MHobHv 2zcuDztfg==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kIJwB-00083q-7y; Tue, 15 Sep 2020 23:00:35 +0000 Received: from kernel.crashing.org ([76.164.61.194]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kIJw9-00083T-19 for linux-arm-kernel@lists.infradead.org; Tue, 15 Sep 2020 23:00:33 +0000 Received: from localhost (gate.crashing.org [63.228.1.57]) (authenticated bits=0) by kernel.crashing.org (8.14.7/8.14.7) with ESMTP id 08FN0AAr012347 (version=TLSv1/SSLv3 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Tue, 15 Sep 2020 18:00:14 -0500 Message-ID: <28c9039eba4bc288abb8ab1b82b51c16023fcb3c.camel@kernel.crashing.org> Subject: Re: [PATCH] arm64: Enable PCI write-combine resources under sysfs From: Benjamin Herrenschmidt To: Lorenzo Pieralisi Date: Wed, 16 Sep 2020 09:00:09 +1000 In-Reply-To: <20200915101831.GA2616@e121166-lin.cambridge.arm.com> References: <20200910232938.GJ904879@nvidia.com> <3110e00a1f4df7b7359ba4f2b7f86a35aa47405e.camel@kernel.crashing.org> <20200911214225.hml2wbbq2rofn4re@amazon.com> <20200914141726.GA904879@nvidia.com> <20200914142406.k44zrnp2wdsandsp@amazon.com> <20200914143819.GC904879@nvidia.com> <375c478593945a416f3180c3773bcb5240d2e36c.camel@kernel.crashing.org> <1d6f2ceb8d3538c906a1fdb8cd3d4c74ccffa42e.camel@kernel.crashing.org> <20200914225740.GP904879@nvidia.com> <2b539df4c9ec703458e46da2fc879ee3b310b31c.camel@kernel.crashing.org> <20200915101831.GA2616@e121166-lin.cambridge.arm.com> X-Mailer: Evolution 3.28.5-0ubuntu0.18.04.2 Mime-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200915_190033_214528_23268D23 X-CRM114-Status: GOOD ( 22.52 ) 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: Leon Romanovsky , linux-pci@vger.kernel.org, Bjorn Helgaas , Jason Gunthorpe , catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, Clint Sbisa Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, 2020-09-15 at 11:18 +0100, Lorenzo Pieralisi wrote: > > It's useful for random things, I've used it quite a bit in a previous > > life for things like in-lab hw testing etc... There's tooling out > > there, esp. in the more 'embedded' side of thing that uses this, I > > don't see a good reason not to provide the same level of functionality. > > > > So Lorenzo, imho, we should merge the patch. > > To sum it up: > > (1) RDMA drivers need a new mapping function/attribute to define their > message push model. Actually the message model is not necessarily related > to write combining a la x86, so we should probably come up with a better > and consistent naming. Enabling this patchset may trigger performance > regressions on mellanox drivers on arm64 - this ought to be addressed. I doubt it. Besides Mellanox will probably enable WC already through the other code path (the use of this accessor is only one of the path that enables the driver to do WC). I don't think we need to solve the RDMA semantics issue that urgently TBH, and it's definitely an orthogonal issue to that at hand. > (2) User-space/passthrough drivers rely on VFIO for BAR mappings. Since > it looks relevant, WC message model semantics should be introduced > there, somehow. Yes. > (3) Given the above, the sysfs interface can be enabled. I still don't > see the advantages (other than saying it is there for other arches, ie > what can you really do with the sysfs mappings - see Jason's VFIO/DMA > query) but we can do it. Still, I am not happy about the possible > mellanox regressions - that should be tested/verified before this > patch is merged IMHO. Do we really need it for v5.10 ? I don't think there's a significant risk of regression, but then I also dont' have a way to test :-) Cheers, Ben. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel