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=-5.3 required=3.0 tests=BAYES_00, 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 43A2DC4363D for ; Fri, 25 Sep 2020 04:14:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0B16321D20 for ; Fri, 25 Sep 2020 04:14:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727056AbgIYEOb (ORCPT ); Fri, 25 Sep 2020 00:14:31 -0400 Received: from verein.lst.de ([213.95.11.211]:54541 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726758AbgIYEO2 (ORCPT ); Fri, 25 Sep 2020 00:14:28 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id 0871E68AFE; Fri, 25 Sep 2020 06:14:26 +0200 (CEST) Date: Fri, 25 Sep 2020 06:14:25 +0200 From: 'Christoph Hellwig' To: David Laight Cc: 'Christoph Hellwig' , "iommu@lists.linux-foundation.org" , Dominik Brodowski , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 3/3] dma-mapping: better document dma_addr_t and DMA_MAPPING_ERROR Message-ID: <20200925041425.GA9419@lst.de> References: <20200922134002.1227279-1-hch@lst.de> <20200922134002.1227279-4-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) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 22, 2020 at 01:56:46PM +0000, David Laight wrote: > > +/* > > + * A dma_addr_t can hold any valid DMA or bus address for the platform. It can > > + * be given to a device to use as a DMA source or target. A CPU cannot > > + * reference a dma_addr_t directly because there may be translation between its > > + * physical address space and the bus address space. > > It can't access it 'directly' because it isn't a virtual address.... > > > + * > > + * DMA_MAPPING_ERROR is the magic error code if a mapping failed. It should not > > + * be used directly in drivers, but checked for using dma_mapping_error() > > + * instead. > > + */ > > I think it might be worth adding: > > A dma_addr_t value may be device dependant and differ from the > 'physical address' of the memory. This is what I've committed: * A dma_addr_t can hold any valid DMA or bus address for the platform. It can * be given to a device to use as a DMA source or target. It is specific to a * given device and there may be a translation between the CPU physical address * space and the bus address space.