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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,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 F39A1C32753 for ; Fri, 2 Aug 2019 08:14:50 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 CC9DA20679 for ; Fri, 2 Aug 2019 08:14:50 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="U6+Qau7n" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CC9DA20679 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=USZF96Gj3w8zdOIea6kGoF5IsO3EVq+i1Z9L6wmbvS0=; b=U6+Qau7nnhjlv6 BeHZsocwaH3k2xoVQZvlFKJzloFksrDrRdldmMnHpsLGrEOHSkbaief6JgN8PPYhJemB+ItRI7NQw f+KhE0DFoD3jALnNikcb8vvu3m0Y0TbQm+wL0IZQFpqTfMPCp9Ut+DWx4lwLs8lo3jpn9/5uN5PvT f7CmUUMf3MXQ51SI3972dv96PZ6NM3tz25dXOuFTLC5EZVU+HznWcTVAMYXCvidX9BFineqqcn/q4 BvCORs9kGKf4xIqUMoINCQ7Fgj8Jq+htN5mHf8fyFnvSZasSWd0D+5bMnxpSX3ZpVwjlvXhinTNOP qCIJF10U6qG/aRL3aYeA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1htSi9-0004ew-HF; Fri, 02 Aug 2019 08:14:49 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1htSi6-0004e1-I7 for linux-arm-kernel@lists.infradead.org; Fri, 02 Aug 2019 08:14:47 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id 9F17E68B05; Fri, 2 Aug 2019 10:14:41 +0200 (CEST) Date: Fri, 2 Aug 2019 10:14:41 +0200 From: Christoph Hellwig To: Will Deacon Subject: Re: [PATCH] dma-mapping: fix page attributes for dma_mmap_* Message-ID: <20190802081441.GA9725@lst.de> References: <20190801142118.21225-1-hch@lst.de> <20190801142118.21225-2-hch@lst.de> <20190801162305.3m32chycsdjmdejk@willie-the-truck> <20190801163457.GB26588@lst.de> <20190801164411.kmsl4japtfkgvzxe@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190801164411.kmsl4japtfkgvzxe@willie-the-truck> User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190802_011446_758197_C7454B49 X-CRM114-Status: GOOD ( 15.32 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Aug 01, 2019 at 05:44:12PM +0100, Will Deacon wrote: > > > 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. > > How about arch_dma_noncoherent_mmap_pgprot() ? Too long? Sounds a little long yes. And doesn't fix the additional problem that we don't just it for mmap but also for the in-kernel remapping these days. > > 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. > > Or it's always been busted and happens to work out in practice... I've sent a ping to the mips folks. While we'are at it: arm64 and arm32 (optionally) map dma coherent allocations as write combine. I suspect this hasn't always just been busted but intentional (of course!), but is there any chance to get a quote from the arm architecture spec on why this is fine as it looks rather confusion? Also if we assume mips is buggy DMA_ATTR_WRITE_COMBINE really just seems to be there for old arm platforms, which makes the scope pretty limited. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel