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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 1BC2FCA90AF for ; Wed, 13 May 2020 13:24:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9ED48204EC for ; Wed, 13 May 2020 13:24:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733104AbgEMNYc (ORCPT ); Wed, 13 May 2020 09:24:32 -0400 Received: from foss.arm.com ([217.140.110.172]:45904 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726001AbgEMNYc (ORCPT ); Wed, 13 May 2020 09:24:32 -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 4D34C30E; Wed, 13 May 2020 06:24:31 -0700 (PDT) Received: from [10.57.36.85] (unknown [10.57.36.85]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9C35C3F71E; Wed, 13 May 2020 06:24:27 -0700 (PDT) Subject: Re: [PATCH v4 02/38] scatterlist: add generic wrappers for iterating over sgtable objects To: Marek Szyprowski , dri-devel@lists.freedesktop.org, iommu@lists.linux-foundation.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org Cc: Christoph Hellwig , Bartlomiej Zolnierkiewicz , linux-arm-kernel@lists.infradead.org, David Airlie , Daniel Vetter References: <20200512085710.14688-1-m.szyprowski@samsung.com> <20200512090058.14910-1-m.szyprowski@samsung.com> <20200512090058.14910-2-m.szyprowski@samsung.com> From: Robin Murphy Message-ID: <4f9f747a-9bce-90f4-9ca7-ab851f29d758@arm.com> Date: Wed, 13 May 2020 14:24:25 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200512090058.14910-2-m.szyprowski@samsung.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-05-12 10:00 am, Marek Szyprowski wrote: > struct sg_table is a common structure used for describing a memory > buffer. It consists of a scatterlist with memory pages and DMA addresses > (sgl entry), as well as the number of scatterlist entries: CPU pages > (orig_nents entry) and DMA mapped pages (nents entry). > > It turned out that it was a common mistake to misuse nents and orig_nents > entries, calling the scatterlist iterating functions with a wrong number > of the entries. > > To avoid such issues, lets introduce a common wrappers operating directly > on the struct sg_table objects, which take care of the proper use of > the nents and orig_nents entries. > > While touching this, lets clarify some ambiguities in the comments for > the existing for_each helpers. Reviewed-by: Robin Murphy > Signed-off-by: Marek Szyprowski > --- > For more information, see '[PATCH v4 00/38] DRM: fix struct sg_table nents > vs. orig_nents misuse' thread: > https://lore.kernel.org/dri-devel/20200512085710.14688-1-m.szyprowski@samsung.com/T/ > --- > include/linux/scatterlist.h | 50 ++++++++++++++++++++++++++++++++++++++++++--- > 1 file changed, 47 insertions(+), 3 deletions(-) > > diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h > index 6eec50f..4f922af 100644 > --- a/include/linux/scatterlist.h > +++ b/include/linux/scatterlist.h > @@ -151,6 +151,20 @@ static inline void sg_set_buf(struct scatterlist *sg, const void *buf, > #define for_each_sg(sglist, sg, nr, __i) \ > for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg)) > > +/* > + * Loop over each sg element in the given sg_table object. > + */ > +#define for_each_sgtable_sg(sgt, sg, i) \ > + for_each_sg(sgt->sgl, sg, sgt->orig_nents, i) > + > +/* > + * Loop over each sg element in the given *DMA mapped* sg_table object. > + * Please use sg_dma_address(sg) and sg_dma_len(sg) to extract DMA addresses > + * of the each element. > + */ > +#define for_each_sgtable_dma_sg(sgt, sg, i) \ > + for_each_sg(sgt->sgl, sg, sgt->nents, i) > + > /** > * sg_chain - Chain two sglists together > * @prv: First scatterlist > @@ -401,9 +415,10 @@ static inline struct page *sg_page_iter_page(struct sg_page_iter *piter) > * @sglist: sglist to iterate over > * @piter: page iterator to hold current page, sg, sg_pgoffset > * @nents: maximum number of sg entries to iterate over > - * @pgoffset: starting page offset > + * @pgoffset: starting page offset (in pages) > * > * Callers may use sg_page_iter_page() to get each page pointer. > + * In each loop it operates on PAGE_SIZE unit. > */ > #define for_each_sg_page(sglist, piter, nents, pgoffset) \ > for (__sg_page_iter_start((piter), (sglist), (nents), (pgoffset)); \ > @@ -412,18 +427,47 @@ static inline struct page *sg_page_iter_page(struct sg_page_iter *piter) > /** > * for_each_sg_dma_page - iterate over the pages of the given sg list > * @sglist: sglist to iterate over > - * @dma_iter: page iterator to hold current page > + * @dma_iter: DMA page iterator to hold current page > * @dma_nents: maximum number of sg entries to iterate over, this is the value > * returned from dma_map_sg > - * @pgoffset: starting page offset > + * @pgoffset: starting page offset (in pages) > * > * Callers may use sg_page_iter_dma_address() to get each page's DMA address. > + * In each loop it operates on PAGE_SIZE unit. > */ > #define for_each_sg_dma_page(sglist, dma_iter, dma_nents, pgoffset) \ > for (__sg_page_iter_start(&(dma_iter)->base, sglist, dma_nents, \ > pgoffset); \ > __sg_page_iter_dma_next(dma_iter);) > > +/** > + * for_each_sgtable_page - iterate over all pages in the sg_table object > + * @sgt: sg_table object to iterate over > + * @piter: page iterator to hold current page > + * @pgoffset: starting page offset (in pages) > + * > + * Iterates over the all memory pages in the buffer described by > + * a scatterlist stored in the given sg_table object. > + * See also for_each_sg_page(). In each loop it operates on PAGE_SIZE unit. > + */ > +#define for_each_sgtable_page(sgt, piter, pgoffset) \ > + for_each_sg_page(sgt->sgl, piter, sgt->orig_nents, pgoffset) > + > +/** > + * for_each_sgtable_dma_page - iterate over the DMA mapped sg_table object > + * @sgt: sg_table object to iterate over > + * @dma_iter: DMA page iterator to hold current page > + * @pgoffset: starting page offset (in pages) > + * > + * Iterates over the all DMA mapped pages in the buffer described by > + * a scatterlist stored in the given sg_table object. > + * See also for_each_sg_dma_page(). In each loop it operates on PAGE_SIZE > + * unit. > + */ > +#define for_each_sgtable_dma_page(sgt, dma_iter, pgoffset) \ > + for_each_sg_dma_page(sgt->sgl, dma_iter, sgt->nents, pgoffset) > + > + > /* > * Mapping sg iterator > * >