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From:   Marek Szyprowski <m.szyprowski@samsung.com>
To:     dri-devel@lists.freedesktop.org, iommu@lists.linux-foundation.org,
        linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org
Cc:     Marek Szyprowski <m.szyprowski@samsung.com>,
        Christoph Hellwig <hch@lst.de>,
        Robin Murphy <robin.murphy@arm.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        Benjamin Gaignard <benjamin.gaignard@linaro.org>,
        intel-gfx@lists.freedesktop.org,
        linux-arm-kernel@lists.infradead.org,
        amd-gfx@lists.freedesktop.org, David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>
Subject: [RFC 09/17] drm: panfrost: fix sg_table nents vs. orig_nents misuse
Date:   Tue, 28 Apr 2020 15:19:57 +0200
Message-Id: <20200428132005.21424-10-m.szyprowski@samsung.com>
In-Reply-To: <20200428132005.21424-1-m.szyprowski@samsung.com>
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        <CGME20200428132027eucas1p1a045e89a0058ccff3ea94d1da2236af7@eucas1p1.samsung.com>
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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@samsung.com>
---
 drivers/gpu/drm/panfrost/panfrost_gem.c | 3 ++-
 drivers/gpu/drm/panfrost/panfrost_mmu.c | 4 +++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c
index 17b654e..22fec7c 100644
--- a/drivers/gpu/drm/panfrost/panfrost_gem.c
+++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
@@ -42,7 +42,8 @@ static void panfrost_gem_free_object(struct drm_gem_object *obj)
 		for (i = 0; i < n_sgt; i++) {
 			if (bo->sgts[i].sgl) {
 				dma_unmap_sg(pfdev->dev, bo->sgts[i].sgl,
-					     bo->sgts[i].nents, DMA_BIDIRECTIONAL);
+					     bo->sgts[i].orig_nents,
+					     DMA_BIDIRECTIONAL);
 				sg_free_table(&bo->sgts[i]);
 			}
 		}
diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
index ed28aeb..2d9b1f9 100644
--- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
+++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
@@ -517,7 +517,9 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
 	if (ret)
 		goto err_pages;
 
-	if (!dma_map_sg(pfdev->dev, sgt->sgl, sgt->nents, DMA_BIDIRECTIONAL)) {
+	sgt->nents = dma_map_sg(pfdev->dev, sgt->sgl, sgt->orig_nents,
+				DMA_BIDIRECTIONAL);
+	if (!sgt->nents) {
 		ret = -EINVAL;
 		goto err_map;
 	}
-- 
1.9.1