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 61F44C4363D for ; Fri, 25 Sep 2020 11:15:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 348F220936 for ; Fri, 25 Sep 2020 11:15:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728136AbgIYLPo (ORCPT ); Fri, 25 Sep 2020 07:15:44 -0400 Received: from foss.arm.com ([217.140.110.172]:42402 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727132AbgIYLPn (ORCPT ); Fri, 25 Sep 2020 07:15:43 -0400 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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.