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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Tue, 5 May 2020 11:24:37 +0200
Message-ID: <CAMuHMdVisnijasoxazj+6kUFM3UrTYkVo6kC1dxZv5zK0yD7TQ@mail.gmail.com>
Subject: Re: [PATCH v3 18/25] drm: rcar-du: fix common struct sg_table related issues
To:     Marek Szyprowski <m.szyprowski@samsung.com>
Cc:     DRI Development <dri-devel@lists.freedesktop.org>,
        Linux IOMMU <iommu@lists.linux-foundation.org>,
        linaro-mm-sig@lists.linaro.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Christoph Hellwig <hch@lst.de>,
        Robin Murphy <robin.murphy@arm.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
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Hi Marek,

On Tue, May 5, 2020 at 10:48 AM Marek Szyprowski
<m.szyprowski@samsung.com> wrote:
> The Documentation/DMA-API-HOWTO.txt states that dma_map_sg returns the
> numer of the created entries in the DMA address space. However the
> subsequent calls to dma_sync_sg_for_{device,cpu} and dma_unmap_sg must be
> called with the original number of the entries passed to dma_map_sg. The
> sg_table->nents in turn holds the result of the dma_map_sg call as stated
> in include/linux/scatterlist.h. A common mistake was to ignore a result
> of the dma_map_sg function and don't use the sg_table->orig_nents at all.
>
> To avoid such issues, lets use common dma-mapping wrappers operating
> directly on the struct sg_table objects and adjust references to the
> nents and orig_nents respectively.
>
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> ---
> For more information, see '[PATCH v3 00/25] DRM: fix struct sg_table nents
> vs. orig_nents misuse' thread: https://lkml.org/lkml/2020/5/5/187

For the modern lore-users:
https://lore.kernel.org/r/20200505083926.28503-1-m.szyprowski@samsung.com/

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds