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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 7941EC4363D for ; Tue, 22 Sep 2020 13:56:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3D4FD20936 for ; Tue, 22 Sep 2020 13:56:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726676AbgIVN4v convert rfc822-to-8bit (ORCPT ); Tue, 22 Sep 2020 09:56:51 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]:60787 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726621AbgIVN4v (ORCPT ); Tue, 22 Sep 2020 09:56:51 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-191-B9hMLBLvPqyihacVwf7g7g-1; Tue, 22 Sep 2020 14:56:46 +0100 X-MC-Unique: B9hMLBLvPqyihacVwf7g7g-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Tue, 22 Sep 2020 14:56:46 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Tue, 22 Sep 2020 14:56:46 +0100 From: David Laight To: 'Christoph Hellwig' , "iommu@lists.linux-foundation.org" CC: Dominik Brodowski , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH 3/3] dma-mapping: better document dma_addr_t and DMA_MAPPING_ERROR Thread-Topic: [PATCH 3/3] dma-mapping: better document dma_addr_t and DMA_MAPPING_ERROR Thread-Index: AQHWkOXa3XgKgm/pWkOhIuRYbHODmKl0rUBw Date: Tue, 22 Sep 2020 13:56:46 +0000 Message-ID: References: <20200922134002.1227279-1-hch@lst.de> <20200922134002.1227279-4-hch@lst.de> In-Reply-To: <20200922134002.1227279-4-hch@lst.de> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Christoph Hellwig > Sent: 22 September 2020 14:40 ... > @@ -131,6 +125,16 @@ struct dma_map_ops { > unsigned long (*get_merge_boundary)(struct device *dev); > }; > > +/* > + * 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. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)