From: Andrzej Hajda <a.hajda@samsung.com>
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: linux-samsung-soc@vger.kernel.org,
Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
David Airlie <airlied@linux.ie>,
Seung-Woo Kim <sw0312.kim@samsung.com>,
Robin Murphy <robin.murphy@arm.com>,
Christoph Hellwig <hch@lst.de>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v7 08/36] drm: exynos: fix common struct sg_table related issues
Date: Tue, 7 Jul 2020 11:40:26 +0200 [thread overview]
Message-ID: <53d2ae18-3d60-773f-4544-3c8f55749038@samsung.com> (raw)
In-Reply-To: <20200619103636.11974-9-m.szyprowski@samsung.com>
On 19.06.2020 12:36, Marek Szyprowski wrote:
> 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>
Reviewed-by <a.hajda@samsung.com>
Regards
Andrzej
> ---
> drivers/gpu/drm/exynos/exynos_drm_g2d.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/exynos/exynos_drm_g2d.c b/drivers/gpu/drm/exynos/exynos_drm_g2d.c
> index fcee33a43aca..7014a8cd971a 100644
> --- a/drivers/gpu/drm/exynos/exynos_drm_g2d.c
> +++ b/drivers/gpu/drm/exynos/exynos_drm_g2d.c
> @@ -395,8 +395,8 @@ static void g2d_userptr_put_dma_addr(struct g2d_data *g2d,
> return;
>
> out:
> - dma_unmap_sg(to_dma_dev(g2d->drm_dev), g2d_userptr->sgt->sgl,
> - g2d_userptr->sgt->nents, DMA_BIDIRECTIONAL);
> + dma_unmap_sgtable(to_dma_dev(g2d->drm_dev), g2d_userptr->sgt,
> + DMA_BIDIRECTIONAL, 0);
>
> pages = frame_vector_pages(g2d_userptr->vec);
> if (!IS_ERR(pages)) {
> @@ -511,10 +511,10 @@ static dma_addr_t *g2d_userptr_get_dma_addr(struct g2d_data *g2d,
>
> g2d_userptr->sgt = sgt;
>
> - if (!dma_map_sg(to_dma_dev(g2d->drm_dev), sgt->sgl, sgt->nents,
> - DMA_BIDIRECTIONAL)) {
> + ret = dma_map_sgtable(to_dma_dev(g2d->drm_dev), sgt,
> + DMA_BIDIRECTIONAL, 0);
> + if (ret) {
> DRM_DEV_ERROR(g2d->dev, "failed to map sgt with dma region.\n");
> - ret = -ENOMEM;
> goto err_sg_free_table;
> }
>
next prev parent reply other threads:[~2020-07-07 9:40 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200619103636.11974-1-m.szyprowski@samsung.com>
[not found] ` <CGME20200619103657eucas1p24bff92408adbd4715130fb47595a6187@eucas1p2.samsung.com>
2020-06-19 10:36 ` [PATCH v7 07/36] drm: exynos: use common helper for a scatterlist contiguity check Marek Szyprowski
2020-07-07 9:35 ` Andrzej Hajda
2020-07-07 15:04 ` Andrzej Hajda
2020-07-14 0:28 ` Inki Dae
[not found] ` <CGME20200619103658eucas1p1c3236e2de2798c2d8c02279a9263e9a9@eucas1p1.samsung.com>
2020-06-19 10:36 ` [PATCH v7 08/36] drm: exynos: fix common struct sg_table related issues Marek Szyprowski
2020-07-07 9:40 ` Andrzej Hajda [this message]
2020-07-07 15:05 ` Andrzej Hajda
2020-07-14 0:27 ` Inki Dae
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