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_1 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 15AE4C43461 for ; Wed, 16 Sep 2020 17:02:40 +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 8334D224B0 for ; Wed, 16 Sep 2020 17:02:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="mWBwZ0UU" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8334D224B0 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+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: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=mphbPG95tRD+k+1fuIiXA9L/Bq7KotznBJU0rSYfYg4=; b=mWBwZ0UUVc15XuNRlAWT/tMwI nLYrcKIqZ0Yyjs9FN0CsiSggyssSeb5LBRpYKvFfTQclepM2lRXInWGvT0Os8uILXf7nfKLGwJ9fE yz5q0GY3QKwWsrCNK4NbdFuxSIrXAiu2Jk46NZ14s3pvvyo4iYC/lkAEi+3tx6zpkTuTu8V5d2x1E qmHJh72EUTA9kPm3fGaSE5sItvB+pSBQ0X3Ec8kvUcpQH+dUKXQifXnIwTui85twq9+KcHlZ3cI5x 3JgQfml6jLmKA+oJyiRY5KCa0R1T/02MeT5mmvSvDoI4bPlczWPQFWNPoyRnYAf2woXHnA1ocPbQu hgh3L88Fw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kIans-0003wS-C1; Wed, 16 Sep 2020 17:01:08 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kIano-0003v5-RG for linux-arm-kernel@lists.infradead.org; Wed, 16 Sep 2020 17:01:05 +0000 Received: from gaia (unknown [46.69.195.48]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 2BD39223EA; Wed, 16 Sep 2020 17:01:02 +0000 (UTC) Date: Wed, 16 Sep 2020 18:00:59 +0100 From: Catalin Marinas To: Lorenzo Pieralisi Subject: Re: [PATCH] arm64: Enable PCI write-combine resources under sysfs Message-ID: <20200916170058.GD3122@gaia> References: <1d6f2ceb8d3538c906a1fdb8cd3d4c74ccffa42e.camel@kernel.crashing.org> <20200914225740.GP904879@nvidia.com> <2b539df4c9ec703458e46da2fc879ee3b310b31c.camel@kernel.crashing.org> <20200915101831.GA2616@e121166-lin.cambridge.arm.com> <20200915110511.GQ904879@nvidia.com> <20200915234006.GI1573713@nvidia.com> <20200916083315.GC27496@willie-the-truck> <20200916084851.GA3122@gaia> <20200916141502.GB20770@e121166-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200916141502.GB20770@e121166-lin.cambridge.arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200916_130104_936018_329E47A5 X-CRM114-Status: GOOD ( 22.77 ) 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 , Benjamin Herrenschmidt , Will Deacon , 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 Wed, Sep 16, 2020 at 03:15:02PM +0100, Lorenzo Pieralisi wrote: > On Wed, Sep 16, 2020 at 09:48:52AM +0100, Catalin Marinas wrote: > > On Wed, Sep 16, 2020 at 09:33:16AM +0100, Will Deacon wrote: > > > On Tue, Sep 15, 2020 at 08:40:06PM -0300, Jason Gunthorpe wrote: > > > > On Wed, Sep 16, 2020 at 09:17:38AM +1000, Benjamin Herrenschmidt wrote: > > > > > With the patch, those device will now use MT_DEVICE_NC. > > > > > > > > Which doesn't do WC at all on some ARM implementations. > > > > > > Is that just TX2? I remember that thing being weird where GRE performed > > > better than NC, but I thought that was a one off (and the thing is dead). > > > > I recall something along these lines. Hopefully ARM updated the guidance > > to licensees. > > > > > NC is more permissive than GRE, so I think that's the right one to use; i.e. > > > we go for the fewest number of restrictions on the hardware. If somebody > > > screws up the uarch, that's up to them. > > > > I agree, Normal NC is better as long as the BAR can tolerate read > > side-effects. > > That we don't know but if a prefetchable BAR can't tolerate read > side effects this would be already a problem on eg x86 - that's > the best we can hope for given the current PCI specs. > > +1 on normal NC. The only open point is whether we should make > arch_can_pci_mmap_wc() return false on platforms like TX2. I lost track in this thread whether it matters. TX2 would need Device GRE for optimal performance but the kernel doesn't currently provide it anyway. We could expose a new memory type, aligned_wc ;). -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel