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, USER_AGENT_SANE_1 autolearn=unavailable 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 7C449CA90AF for ; Wed, 13 May 2020 13:23:22 +0000 (UTC) Received: from hemlock.osuosl.org (smtp2.osuosl.org [140.211.166.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E40B5204EC for ; Wed, 13 May 2020 13:23:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E40B5204EC Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by hemlock.osuosl.org (Postfix) with ESMTP id 217DE88794; Wed, 13 May 2020 13:23:22 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from hemlock.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id EB371JzSolXq; Wed, 13 May 2020 13:23:18 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by hemlock.osuosl.org (Postfix) with ESMTP id CCBB2891A0; Wed, 13 May 2020 13:23:18 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id B2533C0178; Wed, 13 May 2020 13:23:18 +0000 (UTC) Received: from fraxinus.osuosl.org (smtp4.osuosl.org [140.211.166.137]) by lists.linuxfoundation.org (Postfix) with ESMTP id BE53FC016F for ; Wed, 13 May 2020 13:23:16 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by fraxinus.osuosl.org (Postfix) with ESMTP id A3E428703D for ; Wed, 13 May 2020 13:23:16 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from fraxinus.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id dZZp9eAeO4EM for ; Wed, 13 May 2020 13:23:14 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by fraxinus.osuosl.org (Postfix) with ESMTP id A74AE87051 for ; Wed, 13 May 2020 13:23:14 +0000 (UTC) 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 2877A30E; Wed, 13 May 2020 06:23:14 -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 5F5103F71E; Wed, 13 May 2020 06:23:12 -0700 (PDT) Subject: Re: [PATCH v4 01/38] dma-mapping: add generic helpers for mapping 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 References: <20200512085710.14688-1-m.szyprowski@samsung.com> <20200512090058.14910-1-m.szyprowski@samsung.com> From: Robin Murphy Message-ID: <400501ec-c56b-edb7-7def-36ad43264123@arm.com> Date: Wed, 13 May 2020 14:23:10 +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: <20200512090058.14910-1-m.szyprowski@samsung.com> Content-Language: en-GB Cc: David Airlie , Daniel Vetter , Christoph Hellwig , linux-arm-kernel@lists.infradead.org, Bartlomiej Zolnierkiewicz X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" 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 DMA-mapping functions with a wrong number of entries or > ignoring the number of mapped entries returned by the dma_map_sg > function. > > To avoid such issues, lets introduce a common wrappers operating directly Nit: "let's" > on the struct sg_table objects, which take care of the proper use of > the nents and orig_nents entries. A few more documentation nitpicks below, but either way the implementation itself (modulo Christoph's fixup) looks good; 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/dma-mapping.h | 79 +++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 79 insertions(+) > > diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h > index b43116a..88f01cc 100644 > --- a/include/linux/dma-mapping.h > +++ b/include/linux/dma-mapping.h > @@ -609,6 +609,85 @@ static inline void dma_sync_single_range_for_device(struct device *dev, > return dma_sync_single_for_device(dev, addr + offset, size, dir); > } > > +/** > + * dma_map_sgtable - Map the given buffer for the DMA operations Either "for DMA operations", "for the DMA operation", or "for a DMA operation", depending on the exact context. Or at that point, perhaps just "for DMA". > + * @dev: The device to perform a DMA operation That doesn't quite parse, maybe "the device performing the DMA operation", or "the device for which to perform the DMA operation", depending on whether "DMA operation" means the mapping or the actual hardware access? > + * @sgt: The sg_table object describing the buffer > + * @dir: DMA direction > + * @attrs: Optional DMA attributes for the map operation > + * > + * Maps a buffer described by a scatterlist stored in the given sg_table > + * object for the @dir DMA operation by the @dev device. After success > + * the ownership for the buffer is transferred to the DMA domain. One has > + * to call dma_sync_sgtable_for_cpu() or dma_unmap_sgtable() to move the > + * ownership of the buffer back to the CPU domain before touching the > + * buffer by the CPU. > + * Returns 0 on success or -EINVAL on error during mapping the buffer. Maybe make that a proper "Return:" section? > + */ > +static inline int dma_map_sgtable(struct device *dev, struct sg_table *sgt, > + enum dma_data_direction dir, unsigned long attrs) > +{ > + int n = dma_map_sg_attrs(dev, sgt->sgl, sgt->orig_nents, dir, attrs); > + > + if (n > 0) { > + sgt->nents = n; > + return 0; > + } > + return -EINVAL; > +} > + > +/** > + * dma_unmap_sgtable - Unmap the given buffer for the DMA operations > + * @dev: The device to perform a DMA operation Same two points as before. > + * @sgt: The sg_table object describing the buffer > + * @dir: DMA direction > + * @attrs: Optional DMA attributes for the map operation Presumably "the unmap operation", although it *is* true that some attributes are expected to match those originally passed to dma_map_sgtable()... not sure if kerneldoc can can stretch to that level of detail concisely ;) > + * > + * Unmaps a buffer described by a scatterlist stored in the given sg_table > + * object for the @dir DMA operation by the @dev device. After this function > + * the ownership of the buffer is transferred back to the CPU domain. > + */ > +static inline void dma_unmap_sgtable(struct device *dev, struct sg_table *sgt, > + enum dma_data_direction dir, unsigned long attrs) > +{ > + dma_unmap_sg_attrs(dev, sgt->sgl, sgt->orig_nents, dir, attrs); > +} > + > +/** > + * dma_sync_sgtable_for_cpu - Synchronize the given buffer for the CPU access s/the CPU/CPU/ > + * @dev: The device to perform a DMA operation As before. > + * @sgt: The sg_table object describing the buffer > + * @dir: DMA direction > + * > + * Performs the needed cache synchronization and moves the ownership of the > + * buffer back to the CPU domain, so it is safe to perform any access to it > + * by the CPU. Before doing any further DMA operations, one has to transfer > + * the ownership of the buffer back to the DMA domain by calling the > + * dma_sync_sgtable_for_device(). > + */ > +static inline void dma_sync_sgtable_for_cpu(struct device *dev, > + struct sg_table *sgt, enum dma_data_direction dir) > +{ > + dma_sync_sg_for_cpu(dev, sgt->sgl, sgt->orig_nents, dir); > +} > + > +/** > + * dma_sync_sgtable_for_device - Synchronize the given buffer for the DMA That one doesn't even > + * @dev: The device to perform a DMA operation As before. But of course, many thanks for taking the effort to add such complete documentation in the first place :) Cheers, Robin. > + * @sgt: The sg_table object describing the buffer > + * @dir: DMA direction > + * > + * Performs the needed cache synchronization and moves the ownership of the > + * buffer back to the DMA domain, so it is safe to perform the DMA operation. > + * Once finished, one has to call dma_sync_sgtable_for_cpu() or > + * dma_unmap_sgtable(). > + */ > +static inline void dma_sync_sgtable_for_device(struct device *dev, > + struct sg_table *sgt, enum dma_data_direction dir) > +{ > + dma_sync_sg_for_device(dev, sgt->sgl, sgt->orig_nents, dir); > +} > + > #define dma_map_single(d, a, s, r) dma_map_single_attrs(d, a, s, r, 0) > #define dma_unmap_single(d, a, s, r) dma_unmap_single_attrs(d, a, s, r, 0) > #define dma_map_sg(d, s, n, r) dma_map_sg_attrs(d, s, n, r, 0) > _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu