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=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 CB96DC433E4 for ; Tue, 14 Jul 2020 11:01:50 +0000 (UTC) Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) (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 9E1C421D79 for ; Tue, 14 Jul 2020 11:01:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9E1C421D79 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id 5AD9D8A5F6; Tue, 14 Jul 2020 11:01:50 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from whitealder.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id aYcSMLPekRvU; Tue, 14 Jul 2020 11:01:48 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by whitealder.osuosl.org (Postfix) with ESMTP id B55048A303; Tue, 14 Jul 2020 11:01:48 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 9E5B0C0888; Tue, 14 Jul 2020 11:01:48 +0000 (UTC) Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) by lists.linuxfoundation.org (Postfix) with ESMTP id 450C1C0733 for ; Tue, 14 Jul 2020 11:01:47 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id 337038A5E7 for ; Tue, 14 Jul 2020 11:01:47 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from whitealder.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id FxprVWjHOUoU for ; Tue, 14 Jul 2020 11:01:45 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by whitealder.osuosl.org (Postfix) with ESMTPS id B81658A303 for ; Tue, 14 Jul 2020 11:01:45 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id D05A568CFC; Tue, 14 Jul 2020 13:01:41 +0200 (CEST) Date: Tue, 14 Jul 2020 13:01:41 +0200 From: Christoph Hellwig To: Robin Murphy Subject: Re: [PATCH 1/4] dma-mapping: Add bounced DMA ops Message-ID: <20200714110141.GD16178@lst.de> References: <20200713091211.2183368-1-tientzu@chromium.org> <20200713091211.2183368-2-tientzu@chromium.org> <4a2451f9-57d8-2e83-e1d6-f144f37173c0@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <4a2451f9-57d8-2e83-e1d6-f144f37173c0@arm.com> User-Agent: Mutt/1.5.17 (2007-11-01) Cc: drinkcat@chromium.org, devicetree@vger.kernel.org, heikki.krogerus@linux.intel.com, saravanak@google.com, suzuki.poulose@arm.com, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, bgolaszewski@baylibre.com, iommu@lists.linux-foundation.org, robh+dt@kernel.org, Claire Chang , dan.j.williams@intel.com, treding@nvidia.com, frowand.list@gmail.com, hch@lst.de X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Mon, Jul 13, 2020 at 12:55:43PM +0100, Robin Murphy wrote: > On 2020-07-13 10:12, Claire Chang wrote: >> The bounced DMA ops provide an implementation of DMA ops that bounce >> streaming DMA in and out of a specially allocated region. Only the >> operations relevant to streaming DMA are supported. > > I think there are too many implicit assumptions here - apparently that > coherent allocations will always be intercepted by > dma_*_from_dev_coherent(), and that calling into dma-direct won't actually > bounce things a second time beyond where you thought they were going, > manage coherency for a different address, and make it all go subtly wrong. > Consider "swiotlb=force", for instance... > > Again, plumbing this straight into dma-direct so that SWIOTLB can simply > target a different buffer and always bounce regardless of masks would seem > a far better option. I haven't really had time to read through the details, but I agree that any bouncing scheme should reuse the swiotlb code and not invent a parallel infrastructure. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu