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,URIBL_BLOCKED,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 864B2C19759 for ; Thu, 1 Aug 2019 16:35:46 +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 5D60B20679 for ; Thu, 1 Aug 2019 16:35:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5D60B20679 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 AA3C221C8; Thu, 1 Aug 2019 16:35:34 +0000 (UTC) Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id D507C130E for ; Thu, 1 Aug 2019 16:35:01 +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 696D55F4 for ; Thu, 1 Aug 2019 16:35:01 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id C7B8E68B20; Thu, 1 Aug 2019 18:34:57 +0200 (CEST) Date: Thu, 1 Aug 2019 18:34:57 +0200 From: Christoph Hellwig To: Will Deacon Subject: Re: [PATCH] dma-mapping: fix page attributes for dma_mmap_* Message-ID: <20190801163457.GB26588@lst.de> References: <20190801142118.21225-1-hch@lst.de> <20190801142118.21225-2-hch@lst.de> <20190801162305.3m32chycsdjmdejk@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190801162305.3m32chycsdjmdejk@willie-the-truck> User-Agent: Mutt/1.5.17 (2007-11-01) Cc: Shawn Anastasio , Michael Ellerman , linuxppc-dev@lists.ozlabs.org, Russell King , linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, Catalin Marinas , Robin Murphy , Christoph Hellwig , linux-arm-kernel@lists.infradead.org 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 Thu, Aug 01, 2019 at 05:23:06PM +0100, Will Deacon wrote: > > - if (!dev_is_dma_coherent(dev) || (attrs & DMA_ATTR_WRITE_COMBINE)) > > - return pgprot_writecombine(prot); > > - return prot; > > + return pgprot_writecombine(prot); > > } > > Seems like a sensible cleanup to me: > > Acked-by: Will Deacon > > Although arch_dma_mmap_pgprot() is a bit of a misnomer now that it only > gets involved in the non-coherent case. A better name is welcome. My other idea would be to just remove it entirely and do something like: #ifndef pgprot_dmacoherent #define pgprot_dmacoherent pgprot_noncached #endif pgprot_t dma_mmap_pgprot(struct device *dev, pgprot_t prot, unsigned long attrs) { if (dev_is_dma_coherent(dev) || (attrs & DMA_ATTR_NON_CONSISTENT)) return prot; #ifdef pgprot_writecombine if (attrs & DMA_ATTR_WRITE_COMBINE) return pgprot_writecombine(prot); #endif return pgprot_dmacoherent(prot); } But my worry is how this interacts with architectures that have an uncached segment (mips, nios2, microblaze, extensa) where we'd have the kernel access DMA_ATTR_WRITE_COMBINE mappigns using the uncached segment, and userspace mmaps using pgprot_writecombine, which could lead to aliasing issues. But then again mips already supports DMA_ATTR_WRITE_COMBINE, so this must be ok somehow. I guess I'll need to field that question to the relevant parties. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu