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Message-Id: <20200619103636.11974-25-m.szyprowski@samsung.com>
Date: Fri, 19 Jun 2020 12:36:24 +0200
From: Marek Szyprowski <m.szyprowski@...sung.com>
To: dri-devel@...ts.freedesktop.org, iommu@...ts.linux-foundation.org,
linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org
Cc: Marek Szyprowski <m.szyprowski@...sung.com>,
Christoph Hellwig <hch@....de>,
Robin Murphy <robin.murphy@....com>,
Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
linux-arm-kernel@...ts.infradead.org,
David Airlie <airlied@...ux.ie>,
Daniel Vetter <daniel@...ll.ch>,
Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>,
xen-devel@...ts.xenproject.org
Subject: [PATCH v7 24/36] drm: xen: fix common struct sg_table related
issues
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.
Fix the code to refer to proper nents or orig_nents entries. This driver
reports the number of the pages in the imported scatterlist, so it should
refer to sg_table->orig_nents entry.
Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
Acked-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
---
drivers/gpu/drm/xen/xen_drm_front_gem.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/xen/xen_drm_front_gem.c b/drivers/gpu/drm/xen/xen_drm_front_gem.c
index f0b85e094111..ba4bdc5590ea 100644
--- a/drivers/gpu/drm/xen/xen_drm_front_gem.c
+++ b/drivers/gpu/drm/xen/xen_drm_front_gem.c
@@ -215,7 +215,7 @@ xen_drm_front_gem_import_sg_table(struct drm_device *dev,
return ERR_PTR(ret);
DRM_DEBUG("Imported buffer of size %zu with nents %u\n",
- size, sgt->nents);
+ size, sgt->orig_nents);
return &xen_obj->base;
}
--
2.17.1
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