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=-2.3 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 E6FA0C3F2CD for ; Mon, 23 Mar 2020 12:55:38 +0000 (UTC) Received: from silver.osuosl.org (smtp3.osuosl.org [140.211.166.136]) (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 9EFFA206F9 for ; Mon, 23 Mar 2020 12:55:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9EFFA206F9 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 silver.osuosl.org (Postfix) with ESMTP id 5FB94228DB; Mon, 23 Mar 2020 12:55:38 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from silver.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 5hJ2UJ-VABw1; Mon, 23 Mar 2020 12:55:37 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by silver.osuosl.org (Postfix) with ESMTP id 5DB55228AE; Mon, 23 Mar 2020 12:55:37 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 53BFBC089F; Mon, 23 Mar 2020 12:55:37 +0000 (UTC) Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) by lists.linuxfoundation.org (Postfix) with ESMTP id CE3EAC0177 for ; Mon, 23 Mar 2020 12:55:35 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id BDA1288197 for ; Mon, 23 Mar 2020 12:55:35 +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 U5tknDAGDTrT for ; Mon, 23 Mar 2020 12:55:34 +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 5C92688187 for ; Mon, 23 Mar 2020 12:55:34 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id 4428E68BEB; Mon, 23 Mar 2020 13:55:30 +0100 (CET) Date: Mon, 23 Mar 2020 13:55:30 +0100 From: Christoph Hellwig To: Robin Murphy Subject: Re: [PATCH 1/2] dma-mapping: add a dma_ops_bypass flag to struct device Message-ID: <20200323125530.GA17038@lst.de> References: <20200320141640.366360-1-hch@lst.de> <20200320141640.366360-2-hch@lst.de> <0a6003e5-8003-4509-4014-4b286d5e8fe0@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <0a6003e5-8003-4509-4014-4b286d5e8fe0@arm.com> User-Agent: Mutt/1.5.17 (2007-11-01) Cc: Greg Kroah-Hartman , "linux-kernel@vger.kernel.org" , "iommu@lists.linux-foundation.org" , "linuxppc-dev@lists.ozlabs.org" , Christoph Hellwig 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, Mar 23, 2020 at 12:14:08PM +0000, Robin Murphy wrote: > On 2020-03-20 2:16 pm, Christoph Hellwig wrote: >> Several IOMMU drivers have a bypass mode where they can use a direct >> mapping if the devices DMA mask is large enough. Add generic support >> to the core dma-mapping code to do that to switch those drivers to >> a common solution. > > Hmm, this is _almost_, but not quite the same as the case where drivers are > managing their own IOMMU mappings, but still need to use streaming DMA for > cache maintenance on the underlying pages. In that case they should simply not call the DMA API at all. We'll just need versions of the cache maintainance APIs that tie in with the raw IOMMU API. > For that we need the ops bypass > to be a "true" bypass and also avoid SWIOTLB regardless of the device's DMA > mask. That behaviour should in fact be fine for the opportunistic bypass > case here as well, since the mask being "big enough" implies by definition > that this should never need to bounce either. In practice it does. But that means adding yet another code path vs the simple direct call to dma_direct_* vs calling the DMA ops which I'd rather avoid. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu