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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,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 CE955C33C9B for ; Thu, 14 Nov 2019 07:35:06 +0000 (UTC) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org [140.211.169.12]) (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 A7666206E1 for ; Thu, 14 Nov 2019 07:35:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A7666206E1 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 mail.linux-foundation.org (localhost [127.0.0.1]) by mail.linuxfoundation.org (Postfix) with ESMTP id 5D30DACD; Thu, 14 Nov 2019 07:35:06 +0000 (UTC) Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id C45E0408 for ; Thu, 14 Nov 2019 07:35:04 +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 smtp1.linuxfoundation.org (Postfix) with ESMTPS id 34C008A for ; Thu, 14 Nov 2019 07:35:04 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id 910B768AFE; Thu, 14 Nov 2019 08:34:59 +0100 (CET) Date: Thu, 14 Nov 2019 08:34:59 +0100 From: Christoph Hellwig To: Nicolas Saenz Julienne Subject: Re: [PATCH] dma-mapping: treat dev->bus_dma_mask as a DMA limit Message-ID: <20191114073459.GB26546@lst.de> References: <20191113161340.27228-1-nsaenzjulienne@suse.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20191113161340.27228-1-nsaenzjulienne@suse.de> User-Agent: Mutt/1.5.17 (2007-11-01) Cc: Peter Zijlstra , Benjamin Herrenschmidt , Dave Hansen , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, linux-ide@vger.kernel.org, Paul Mackerras , Hanjun Guo , Frank Rowand , Christoph Hellwig , "H. Peter Anvin" , Paul Burton , Michael Ellerman , x86@kernel.org, phil@raspberrypi.org, linux-acpi@vger.kernel.org, Ingo Molnar , James Hogan , Len Brown , devicetree@vger.kernel.org, Rob Herring , Borislav Petkov , Andy Lutomirski , Bjorn Helgaas , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, Jens Axboe , linuxppc-dev@lists.ozlabs.org, "Rafael J. Wysocki" , linux-mips@vger.kernel.org, Ralf Baechle , iommu@lists.linux-foundation.org, Sudeep Holla , Robin Murphy X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.12 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 Sender: iommu-bounces@lists.linux-foundation.org Errors-To: iommu-bounces@lists.linux-foundation.org On Wed, Nov 13, 2019 at 05:13:39PM +0100, Nicolas Saenz Julienne wrote: > Using a mask to represent bus DMA constraints has a set of limitations. > The biggest one being it can only hold a power of two (minus one). The > DMA mapping code is already aware of this and treats dev->bus_dma_mask > as a limit. This quirk is already used by some architectures although > still rare. > > With the introduction of the Raspberry Pi 4 we've found a new contender > for the use of bus DMA limits, as its PCIe bus can only address the > lower 3GB of memory (of a total of 4GB). This is impossible to represent > with a mask. To make things worse the device-tree code rounds non power > of two bus DMA limits to the next power of two, which is unacceptable in > this case. > > In the light of this, rename dev->bus_dma_mask to dev->bus_dma_limit all > over the tree and treat it as such. Note that dev->bus_dma_limit is > meant to contain the higher accesible DMA address. This looks sensible modulo the minor comments in this thread. > > Signed-off-by: Nicolas Saenz Julienne > > --- > > Note this is rebased on top of Christoph's latest DMA series: > https://www.spinics.net/lists/arm-kernel/msg768600.html FYI, I'll plan to merge those tonight unless anyone screams. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu