linux-kernel - Re: [PATCH v3 18/25] drm: rcar-du: fix common struct sg

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Date:   Tue, 5 May 2020 11:24:37 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     DRI Development <dri-devel@...ts.freedesktop.org>,
        Linux IOMMU <iommu@...ts.linux-foundation.org>,
        linaro-mm-sig@...ts.linaro.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@....de>,
        Robin Murphy <robin.murphy@....com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH v3 18/25] drm: rcar-du: fix common struct sg_table related issues

Hi Marek,

On Tue, May 5, 2020 at 10:48 AM Marek Szyprowski
<m.szyprowski@...sung.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@...sung.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@...ux-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