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[209.132.180.67]) by mx.google.com with ESMTP id k6si23479257pgr.500.2019.01.12.11.11.24; Sat, 12 Jan 2019 11:11:40 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=intel.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726581AbfALS1N (ORCPT + 99 others); Sat, 12 Jan 2019 13:27:13 -0500 Received: from mga17.intel.com ([192.55.52.151]:63518 "EHLO mga17.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725847AbfALS1M (ORCPT ); Sat, 12 Jan 2019 13:27:12 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmsmga107.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 12 Jan 2019 10:27:12 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,470,1539673200"; d="scan'208";a="137709199" Received: from ssaleem-mobl4.amr.corp.intel.com (HELO ssaleem-mobl1) ([10.254.44.111]) by fmsmga001.fm.intel.com with SMTP; 12 Jan 2019 10:27:10 -0800 Received: by ssaleem-mobl1 (sSMTP sendmail emulation); Sat, 12 Jan 2019 12:27:06 -0600 Date: Sat, 12 Jan 2019 12:27:05 -0600 From: Shiraz Saleem To: Jason Gunthorpe Cc: "linux-rdma@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Christoph Hellwig , Imre Deak , Daniel Vetter , "linux-media@vger.kernel.org" , Yong Zhi , Sakari Ailus , Bingbu Cao , Tian Shu Qiu , Jian Xu Zheng , Sinclair Yeh , Thomas Hellstrom , "dri-devel@lists.freedesktop.org" Subject: Re: [PATCH] lib/scatterlist: Provide a DMA page iterator Message-ID: <20190112182704.GA15320@ssaleem-MOBL4.amr.corp.intel.com> References: <20190104223531.GA1705@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190104223531.GA1705@ziepe.ca> User-Agent: Mutt/1.7.2 (2016-11-26) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 04, 2019 at 10:35:43PM +0000, Jason Gunthorpe wrote: > Commit 2db76d7c3c6d ("lib/scatterlist: sg_page_iter: support sg lists w/o > backing pages") introduced the sg_page_iter_dma_address() function without > providing a way to use it in the general case. If the sg_dma_len is not > equal to the dma_length callers cannot safely use the > for_each_sg_page/sg_page_iter_dma_address combination. > > Resolve this API mistake by providing a DMA specific iterator, > for_each_sg_dma_page(), that uses the right length so > sg_page_iter_dma_address() works as expected with all sglists. A new > iterator type is introduced to provide compile-time safety against wrongly > mixing accessors and iterators. [..] > > +/* > + * sg page iterator for DMA addresses > + * > + * This is the same as sg_page_iter however you can call > + * sg_page_iter_dma_address(@dma_iter) to get the page's DMA > + * address. sg_page_iter_page() cannot be called on this iterator. > + */ Does it make sense to have a variant of sg_page_iter_page() to get the page descriptor with this dma_iter? This can be used when walking DMA-mapped SG lists with for_each_sg_dma_page. > +struct sg_dma_page_iter { > + struct sg_page_iter base; > +}; > + >