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 32E6FC4332B for ; Mon, 23 Mar 2020 08:39:32 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 DEF5E2072D for ; Mon, 23 Mar 2020 08:39:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DEF5E2072D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 48m78x607hzDqwb for ; Mon, 23 Mar 2020 19:39:29 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=none (no SPF record) smtp.mailfrom=lst.de (client-ip=213.95.11.211; helo=verein.lst.de; envelope-from=hch@lst.de; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=lst.de Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 48m76L2MmTzDqpd for ; Mon, 23 Mar 2020 19:37:12 +1100 (AEDT) Received: by verein.lst.de (Postfix, from userid 2407) id 984DB68BEB; Mon, 23 Mar 2020 09:37:05 +0100 (CET) Date: Mon, 23 Mar 2020 09:37:05 +0100 From: Christoph Hellwig To: Alexey Kardashevskiy Subject: Re: [PATCH 1/2] dma-mapping: add a dma_ops_bypass flag to struct device Message-ID: <20200323083705.GA31245@lst.de> References: <20200320141640.366360-1-hch@lst.de> <20200320141640.366360-2-hch@lst.de> <2f31d0dd-aa7e-8b76-c8a1-5759fda5afc9@ozlabs.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2f31d0dd-aa7e-8b76-c8a1-5759fda5afc9@ozlabs.ru> User-Agent: Mutt/1.5.17 (2007-11-01) X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Greg Kroah-Hartman , Joerg Roedel , Robin Murphy , linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, "Aneesh Kumar K.V" , linuxppc-dev@lists.ozlabs.org, Christoph Hellwig , Lu Baolu Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Mon, Mar 23, 2020 at 12:28:34PM +1100, Alexey Kardashevskiy wrote: [full quote deleted, please follow proper quoting rules] > > +static bool dma_alloc_direct(struct device *dev, const struct dma_map_ops *ops) > > +{ > > + if (!ops) > > + return true; > > + > > + /* > > + * Allows IOMMU drivers to bypass dynamic translations if the DMA mask > > + * is large enough. > > + */ > > + if (dev->dma_ops_bypass) { > > + if (min_not_zero(dev->coherent_dma_mask, dev->bus_dma_limit) >= > > + dma_direct_get_required_mask(dev)) > > + return true; > > + } > > > Why not do this in dma_map_direct() as well? Mostly beacuse it is a relatively expensive operation, including a fls64. > Or simply have just one dma_map_direct()? What do you mean with that? > And one more general question - we need a way to use non-direct IOMMU > for RAM above certain limit. > > Let's say we have a system with: > 0 .. 0x1.0000.0000 > 0x100.0000.0000 .. 0x101.0000.0000 > > 2x4G, each is 1TB aligned. And we can map directly only the first 4GB > (because of the maximum IOMMU table size) but not the other. And 1:1 on > that "pseries" is done with offset=0x0800.0000.0000.0000. > > So we want to check every bus address against dev->bus_dma_limit, not > dev->coherent_dma_mask. In the example above I'd set bus_dma_limit to > 0x0800.0001.0000.0000 and 1:1 mapping for the second 4GB would not be > tried. Does this sound reasonable? Thanks, bus_dma_limit is just another limiting factor applied on top of coherent_dma_mask or dma_mask respectively.