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=BAYES_00, 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 B5179C433DF for ; Thu, 20 Aug 2020 05:15:22 +0000 (UTC) Received: from silver.osuosl.org (smtp3.osuosl.org [140.211.166.136]) (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 8B8FD2078B for ; Thu, 20 Aug 2020 05:15:22 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8B8FD2078B 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 localhost (localhost [127.0.0.1]) by silver.osuosl.org (Postfix) with ESMTP id 2D6242151F; Thu, 20 Aug 2020 05:15:22 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from silver.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id GQdrBe9opxdU; Thu, 20 Aug 2020 05:15:21 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by silver.osuosl.org (Postfix) with ESMTP id ED28B2050C; Thu, 20 Aug 2020 05:15:20 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id CA8EFC07FF; Thu, 20 Aug 2020 05:15:20 +0000 (UTC) Received: from fraxinus.osuosl.org (smtp4.osuosl.org [140.211.166.137]) by lists.linuxfoundation.org (Postfix) with ESMTP id 497D5C0051 for ; Thu, 20 Aug 2020 05:15:19 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by fraxinus.osuosl.org (Postfix) with ESMTP id 29C00863E0 for ; Thu, 20 Aug 2020 05:15:19 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from fraxinus.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 59FvW93bgyIO for ; Thu, 20 Aug 2020 05:15:18 +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 fraxinus.osuosl.org (Postfix) with ESMTPS id 64E5A86396 for ; Thu, 20 Aug 2020 05:15:18 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id A894C68BEB; Thu, 20 Aug 2020 07:15:12 +0200 (CEST) Date: Thu, 20 Aug 2020 07:15:12 +0200 From: Christoph Hellwig To: Tomasz Figa Subject: Re: [PATCH 19/28] dma-mapping: replace DMA_ATTR_NON_CONSISTENT with dma_{alloc, free}_pages Message-ID: <20200820051512.GA5141@lst.de> References: <20200819065555.1802761-1-hch@lst.de> <20200819065555.1802761-20-hch@lst.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Cc: alsa-devel@alsa-project.org, linux-ia64@vger.kernel.org, Linux Doc Mailing List , nouveau@lists.freedesktop.org, linux-nvme@lists.infradead.org, linux-mips@vger.kernel.org, "James E.J. Bottomley" , linux-mm@kvack.org, Christoph Hellwig , linux-samsung-soc , Joonyoung Shim , linux-scsi@vger.kernel.org, Kyungmin Park , Ben Skeggs , Matt Porter , Linux Media Mailing List , Tom Lendacky , Pawel Osciak , Mauro Carvalho Chehab , "list@263.net:IOMMU DRIVERS , Joerg Roedel , " , Thomas Bogendoerfer , linux-parisc@vger.kernel.org, netdev@vger.kernel.org, Seung-Woo Kim , Linux Kernel Mailing List , "list@263.net:IOMMU DRIVERS , Joerg Roedel , " X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 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 Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Wed, Aug 19, 2020 at 05:03:52PM +0200, Tomasz Figa wrote: > > > > -Warning: These pieces of the DMA API should not be used in the > > -majority of cases, since they cater for unlikely corner cases that > > -don't belong in usual drivers. > > +These APIs allow to allocate pages that can be used like normal pages > > +in the kernel direct mapping, but are guaranteed to be DMA addressable. > > Could we elaborate a bit more on what "like normal pages in kernel > direct mapping" mean from the driver perspective? It mostly means you can call virt_to_page and then do anything you'd do with a page struct. Unlike dma_alloc_attrs that just return an opaque virtual address that the caller is not allowed to poke into. > There is one aspect that the existing dma_alloc_attrs() handles, but > this new function doesn't: IOMMU support. The function will always > allocate a physically-contiguous block memory, which is a costly > operation and not even guaranteed to succeed, even if enough free > memory is available. > > Modern SoCs employ IOMMUs to avoid the need to allocate > physically-contiguous memory and those happen to be also the devices > that could benefit from non-coherent allocations a lot. One of the > tasks of the DMA API was making it possible to allocate suitable > memory for a given device, without having the driver know about the > SoC integration details, such as the presence of an IOMMU. This is completely out of scope for this API exactly because it guarantees a page in the direct mapping. But see my previous mail in reply to Robin on how you can implement the funtionality you want right now without any help from the dma-mapping subsystem. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu