linux-kernel - [RFC 11/17] drm: rockchip: fix sg_table nents vs. orig

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Date:   Tue, 28 Apr 2020 15:19:59 +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>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        intel-gfx@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        amd-gfx@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Subject: [RFC 11/17] drm: rockchip: fix sg_table nents vs. orig_nents misuse

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 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. Adapt the code to obey those rules.

Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
---
 drivers/gpu/drm/rockchip/rockchip_drm_gem.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
index 0d18846..a024c71 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
@@ -37,7 +37,7 @@ static int rockchip_gem_iommu_map(struct rockchip_gem_object *rk_obj)
 	rk_obj->dma_addr = rk_obj->mm.start;
 
 	ret = iommu_map_sg(private->domain, rk_obj->dma_addr, rk_obj->sgt->sgl,
-			   rk_obj->sgt->nents, prot);
+			   rk_obj->sgt->orig_nents, prot);
 	if (ret < rk_obj->base.size) {
 		DRM_ERROR("failed to map buffer: size=%zd request_size=%zd\n",
 			  ret, rk_obj->base.size);
@@ -98,11 +98,11 @@ static int rockchip_gem_get_pages(struct rockchip_gem_object *rk_obj)
 	 * TODO: Replace this by drm_clflush_sg() once it can be implemented
 	 * without relying on symbols that are not exported.
 	 */
-	for_each_sg(rk_obj->sgt->sgl, s, rk_obj->sgt->nents, i)
+	for_each_sg(rk_obj->sgt->sgl, s, rk_obj->sgt->orig_nents, i)
 		sg_dma_address(s) = sg_phys(s);
 
-	dma_sync_sg_for_device(drm->dev, rk_obj->sgt->sgl, rk_obj->sgt->nents,
-			       DMA_TO_DEVICE);
+	dma_sync_sg_for_device(drm->dev, rk_obj->sgt->sgl,
+			       rk_obj->sgt->orig_nents, DMA_TO_DEVICE);
 
 	return 0;
 
@@ -351,7 +351,8 @@ void rockchip_gem_free_object(struct drm_gem_object *obj)
 			rockchip_gem_iommu_unmap(rk_obj);
 		} else {
 			dma_unmap_sg(drm->dev, rk_obj->sgt->sgl,
-				     rk_obj->sgt->nents, DMA_BIDIRECTIONAL);
+				     rk_obj->sgt->orig_nents,
+				     DMA_BIDIRECTIONAL);
 		}
 		drm_prime_gem_destroy(obj, rk_obj->sgt);
 	} else {
@@ -493,14 +494,14 @@ static unsigned long rockchip_sg_get_contiguous_size(struct sg_table *sgt,
 			struct sg_table *sg,
 			struct rockchip_gem_object *rk_obj)
 {
-	int count = dma_map_sg(drm->dev, sg->sgl, sg->nents,
+	int count = dma_map_sg(drm->dev, sg->sgl, sg->orig_nents,
 			       DMA_BIDIRECTIONAL);
 	if (!count)
 		return -EINVAL;
 
 	if (rockchip_sg_get_contiguous_size(sg, count) < attach->dmabuf->size) {
 		DRM_ERROR("failed to map sg_table to contiguous linear address.\n");
-		dma_unmap_sg(drm->dev, sg->sgl, sg->nents,
+		dma_unmap_sg(drm->dev, sg->sgl, sg->orig_nents,
 			     DMA_BIDIRECTIONAL);
 		return -EINVAL;
 	}
-- 
1.9.1