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=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 677D1C4727D for ; Fri, 25 Sep 2020 11:15:45 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A5DFE208A9 for ; Fri, 25 Sep 2020 11:15:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A5DFE208A9 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 224A7900005; Fri, 25 Sep 2020 07:15:44 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 1D4B5900002; Fri, 25 Sep 2020 07:15:44 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0EBC0900005; Fri, 25 Sep 2020 07:15:44 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0229.hostedemail.com [216.40.44.229]) by kanga.kvack.org (Postfix) with ESMTP id EB93A900002 for ; Fri, 25 Sep 2020 07:15:43 -0400 (EDT) Received: from smtpin02.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id B4A20824999B for ; Fri, 25 Sep 2020 11:15:43 +0000 (UTC) X-FDA: 77301328566.02.north64_53182f427167 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin02.hostedemail.com (Postfix) with ESMTP id 93CA7101ADEA9 for ; Fri, 25 Sep 2020 11:15:43 +0000 (UTC) X-HE-Tag: north64_53182f427167 X-Filterd-Recvd-Size: 3095 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf20.hostedemail.com (Postfix) with ESMTP for ; Fri, 25 Sep 2020 11:15:42 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 34B1D101E; Fri, 25 Sep 2020 04:15:42 -0700 (PDT) Received: from [10.57.48.76] (unknown [10.57.48.76]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 986323F70D; Fri, 25 Sep 2020 04:15:38 -0700 (PDT) Subject: Re: [PATCH 08/18] dma-mapping: add a new dma_alloc_noncoherent API To: Christoph Hellwig , Mauro Carvalho Chehab , Thomas Bogendoerfer , "James E.J. Bottomley" , Joonyoung Shim , Seung-Woo Kim , Ben Skeggs , Marek Szyprowski , Tomasz Figa , Matt Porter , iommu@lists.linux-foundation.org Cc: alsa-devel@alsa-project.org, linux-samsung-soc@vger.kernel.org, linux-scsi@vger.kernel.org, linux-parisc@vger.kernel.org, linux-doc@vger.kernel.org, nouveau@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, linux-mm@kvack.org, Stefan Richter , netdev@vger.kernel.org, linux1394-devel@lists.sourceforge.net, linux-arm-kernel@lists.infradead.org, linux-media@vger.kernel.org References: <20200915155122.1768241-1-hch@lst.de> <20200915155122.1768241-9-hch@lst.de> From: Robin Murphy Message-ID: Date: Fri, 25 Sep 2020 12:15:37 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.2.2 MIME-Version: 1.0 In-Reply-To: <20200915155122.1768241-9-hch@lst.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2020-09-15 16:51, Christoph Hellwig wrote: [...] > +These APIs allow to allocate pages in the kernel direct mapping that are > +guaranteed to be DMA addressable. This means that unlike dma_alloc_coherent, > +virt_to_page can be called on the resulting address, and the resulting Nit: if we explicitly describe this as if it's a guarantee that can be relied upon... > +struct page can be used for everything a struct page is suitable for. [...] > +This routine allocates a region of bytes of consistent memory. It > +returns a pointer to the allocated region (in the processor's virtual address > +space) or NULL if the allocation failed. The returned memory may or may not > +be in the kernels direct mapping. Drivers must not call virt_to_page on > +the returned memory region. ...then forbid this document's target audience from relying on it, something seems off. At the very least it's unhelpfully unclear :/ Given patch #17, I suspect that the first paragraph is the one that's no longer true. Robin.