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=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 B6585C54E4A for ; Tue, 12 May 2020 12:18:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9658B206CC for ; Tue, 12 May 2020 12:18:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729676AbgELMSa (ORCPT ); Tue, 12 May 2020 08:18:30 -0400 Received: from verein.lst.de ([213.95.11.211]:40890 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729437AbgELMSM (ORCPT ); Tue, 12 May 2020 08:18:12 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id 8F23F68BEB; Tue, 12 May 2020 14:18:08 +0200 (CEST) Date: Tue, 12 May 2020 14:18:08 +0200 From: Christoph Hellwig To: Marek Szyprowski Cc: dri-devel@lists.freedesktop.org, iommu@lists.linux-foundation.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org, Christoph Hellwig , Robin Murphy , Bartlomiej Zolnierkiewicz , linux-arm-kernel@lists.infradead.org, David Airlie , Daniel Vetter Subject: Re: [PATCH v4 01/38] dma-mapping: add generic helpers for mapping sgtable objects Message-ID: <20200512121808.GA20393@lst.de> References: <20200512085710.14688-1-m.szyprowski@samsung.com> <20200512090058.14910-1-m.szyprowski@samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200512090058.14910-1-m.szyprowski@samsung.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 12, 2020 at 11:00:21AM +0200, 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 > on the struct sg_table objects, which take care of the proper use of > the nents and orig_nents entries. > > 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 > + * @dev: The device to perform a DMA operation > + * @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. > + */ > +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; Nit: code tend to be a tad easier to read if the the exceptional condition is inside the branch block, so: if (n <= 0) return -EINVAL; sgt->nents = n; return 0; Otherwise this looks good to me: Reviewed-by: Christoph Hellwig