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Subject: Re: [PATCH v5 33/38] staging: tegra-vde: fix common struct sg_table
 related issues
To:     Marek Szyprowski <m.szyprowski@samsung.com>,
        dri-devel@lists.freedesktop.org, iommu@lists.linux-foundation.org,
        linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org
Cc:     Christoph Hellwig <hch@lst.de>,
        Robin Murphy <robin.murphy@arm.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        linux-arm-kernel@lists.infradead.org,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Thierry Reding <thierry.reding@gmail.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        linux-media@vger.kernel.org, linux-tegra@vger.kernel.org,
        devel@driverdev.osuosl.org
References: <20200513132114.6046-1-m.szyprowski@samsung.com>
 <20200513133245.6408-1-m.szyprowski@samsung.com>
 <CGME20200513133321eucas1p13acea3aa6219ce5f7076c7677ef9eae3@eucas1p1.samsung.com>
 <20200513133245.6408-33-m.szyprowski@samsung.com>
From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <43f9f3cc-2afa-cec3-0dd4-335746ec886e@gmail.com>
Date:   Thu, 14 May 2020 23:07:10 +0300
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13.05.2020 16:32, Marek Szyprowski пишет:
> The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg() function
> returns the number of the created entries in the DMA address space.
> However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and
> dma_unmap_sg must be called with the original number of the entries
> passed to the dma_map_sg().
> 
> struct sg_table is a common structure used for describing a non-contiguous
> memory buffer, used commonly in the DRM and graphics subsystems. 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 use a common dma-mapping wrappers operating
> directly on the struct sg_table objects and use scatterlist page
> iterators where possible. This, almost always, hides references to the
> nents and orig_nents entries, making the code robust, easier to follow
> and copy/paste safe.
> 
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> ---
> For more information, see '[PATCH v5 00/38] DRM: fix struct sg_table nents
> vs. orig_nents misuse' thread:
> https://lore.kernel.org/linux-iommu/20200513132114.6046-1-m.szyprowski@samsung.com/T/
> ---
>  drivers/staging/media/tegra-vde/iommu.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/media/tegra-vde/iommu.c b/drivers/staging/media/tegra-vde/iommu.c
> index 6af863d..adf8dc7 100644
> --- a/drivers/staging/media/tegra-vde/iommu.c
> +++ b/drivers/staging/media/tegra-vde/iommu.c
> @@ -36,8 +36,8 @@ int tegra_vde_iommu_map(struct tegra_vde *vde,
>  
>  	addr = iova_dma_addr(&vde->iova, iova);
>  
> -	size = iommu_map_sg(vde->domain, addr, sgt->sgl, sgt->nents,
> -			    IOMMU_READ | IOMMU_WRITE);
> +	size = iommu_map_sgtable(vde->domain, addr, sgt,
> +				 IOMMU_READ | IOMMU_WRITE);
>  	if (!size) {
>  		__free_iova(&vde->iova, iova);
>  		return -ENXIO;
> 

Reviewed-by: Dmitry Osipenko <digetx@gmail.com>