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,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,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 72B83C433E1 for ; Thu, 20 Aug 2020 05:16:16 +0000 (UTC) Received: from alsa0.perex.cz (alsa0.perex.cz [77.48.224.243]) (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 CC4C920786 for ; Thu, 20 Aug 2020 05:16:15 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alsa-project.org header.i=@alsa-project.org header.b="SkzlkNUJ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CC4C920786 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=alsa-devel-bounces@alsa-project.org Received: from alsa1.perex.cz (alsa1.perex.cz [207.180.221.201]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by alsa0.perex.cz (Postfix) with ESMTPS id 5439C1668; Thu, 20 Aug 2020 07:15:24 +0200 (CEST) DKIM-Filter: OpenDKIM Filter v2.11.0 alsa0.perex.cz 5439C1668 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=alsa-project.org; s=default; t=1597900574; bh=oM2b0m8qtPYoI+q1QGUr+uiwv1PyvIGFKoJQxzyxVlU=; h=Date:From:To:Subject:References:In-Reply-To:Cc:List-Id: List-Unsubscribe:List-Archive:List-Post:List-Help:List-Subscribe: From; b=SkzlkNUJj4OtJp14gwtSzy7ojVruD2UU1OwxY9RGETUgYa00diXfQk6AE4iSGjbSv qEG4vGUXV/1YiSnPcQ3gUkHcUWDdF95C5A+orImaswCLedYuIvTNdSLkRR8pI+5fIR MDGBEq8J9ldaLJjMHzGS0kbSJu55hYYJ2HOiAs9c= Received: from alsa1.perex.cz (localhost.localdomain [127.0.0.1]) by alsa1.perex.cz (Postfix) with ESMTP id C956CF801F9; Thu, 20 Aug 2020 07:15:23 +0200 (CEST) Received: by alsa1.perex.cz (Postfix, from userid 50401) id DA374F80228; Thu, 20 Aug 2020 07:15:21 +0200 (CEST) Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by alsa1.perex.cz (Postfix) with ESMTPS id 0E2E8F80114 for ; Thu, 20 Aug 2020 07:15:14 +0200 (CEST) DKIM-Filter: OpenDKIM Filter v2.11.0 alsa1.perex.cz 0E2E8F80114 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-Type: text/plain; charset=us-ascii 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 , Marek Szyprowski , 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: alsa-devel@alsa-project.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: "Alsa-devel mailing list for ALSA developers - http://www.alsa-project.org" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: "Alsa-devel" 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.