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 58DC5C4332E for ; Mon, 23 Mar 2020 08:37:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 07F442072D for ; Mon, 23 Mar 2020 08:37:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727590AbgCWIhJ (ORCPT ); Mon, 23 Mar 2020 04:37:09 -0400 Received: from verein.lst.de ([213.95.11.211]:57574 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727477AbgCWIhI (ORCPT ); Mon, 23 Mar 2020 04:37:08 -0400 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 Cc: Christoph Hellwig , iommu@lists.linux-foundation.org, linuxppc-dev@lists.ozlabs.org, Lu Baolu , Greg Kroah-Hartman , Joerg Roedel , Robin Murphy , linux-kernel@vger.kernel.org, "Aneesh Kumar K.V" 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) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.