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,USER_AGENT_SANE_1 autolearn=unavailable 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 B96F9C432C3 for ; Thu, 21 Nov 2019 15:26:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9565220674 for ; Thu, 21 Nov 2019 15:26:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727247AbfKUP05 (ORCPT ); Thu, 21 Nov 2019 10:26:57 -0500 Received: from verein.lst.de ([213.95.11.211]:46733 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726563AbfKUP05 (ORCPT ); Thu, 21 Nov 2019 10:26:57 -0500 Received: by verein.lst.de (Postfix, from userid 2407) id 9128268BFE; Thu, 21 Nov 2019 16:26:50 +0100 (CET) Date: Thu, 21 Nov 2019 16:26:50 +0100 From: Christoph Hellwig To: Nicolas Saenz Julienne Cc: Dave Hansen , Andy Lutomirski , Peter Zijlstra , Bjorn Helgaas , Lorenzo Pieralisi , Hanjun Guo , Sudeep Holla , Jens Axboe , Joerg Roedel , Rob Herring , Frank Rowand , Christoph Hellwig , Marek Szyprowski , Robin Murphy , Ralf Baechle , Paul Burton , James Hogan , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , x86@kernel.org, "Rafael J. Wysocki" , Len Brown , linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-pci@vger.kernel.org, linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-ide@vger.kernel.org, iommu@lists.linux-foundation.org, devicetree@vger.kernel.org Subject: Re: [PATCH v2] dma-mapping: treat dev->bus_dma_mask as a DMA limit Message-ID: <20191121152650.GA651@lst.de> References: <20191121092646.8449-1-nsaenzjulienne@suse.de> <20191121152457.GA525@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191121152457.GA525@lst.de> 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 Thu, Nov 21, 2019 at 04:24:57PM +0100, Christoph Hellwig wrote: > On Thu, Nov 21, 2019 at 10:26:44AM +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 should > > contain the higher accesible DMA address. > > > > Signed-off-by: Nicolas Saenz Julienne > > I've tentatively added this patch to the dma-mapping tree based on > Robins principal approval of the last version. That way tomorrows > linux-next run should still pick it up. Actually. This doesn't apply because the dma-mapping tree doesn't have you zone_dma_bits change. I guess we'll need to wait for the next merge window, or maybe post rc1 if this happens to fix the powerpc problem that Christian reported.