drm: tegra: 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.

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: Robin Murphy <robin.murphy@arm.com>

diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
index 723df14..01d94be 100644 (file)
--- a/drivers/gpu/drm/tegra/gem.c
+++ b/drivers/gpu/drm/tegra/gem.c
@@ -98,8 +98,8 @@ static struct sg_table *tegra_bo_pin(struct device *dev, struct host1x_bo *bo,
                 * the SG table needs to be copied to avoid overwriting any
                 * other potential users of the original SG table.
                 */
-               err = sg_alloc_table_from_sg(sgt, obj->sgt->sgl, obj->sgt->nents,
-                                            GFP_KERNEL);
+               err = sg_alloc_table_from_sg(sgt, obj->sgt->sgl,
+                                            obj->sgt->orig_nents, GFP_KERNEL);
                if (err < 0)
                        goto free;
        } else {
@@ -196,8 +196,7 @@ static int tegra_bo_iommu_map(struct tegra_drm *tegra, struct tegra_bo *bo)
 
        bo->iova = bo->mm->start;
 
-       bo->size = iommu_map_sg(tegra->domain, bo->iova, bo->sgt->sgl,
-                               bo->sgt->nents, prot);
+       bo->size = iommu_map_sgtable(tegra->domain, bo->iova, bo->sgt, prot);
        if (!bo->size) {
                dev_err(tegra->drm->dev, "failed to map buffer\n");
                err = -ENOMEM;
@@ -264,8 +263,7 @@ free:
 static void tegra_bo_free(struct drm_device *drm, struct tegra_bo *bo)
 {
        if (bo->pages) {
-               dma_unmap_sg(drm->dev, bo->sgt->sgl, bo->sgt->nents,
-                            DMA_FROM_DEVICE);
+               dma_unmap_sgtable(drm->dev, bo->sgt, DMA_FROM_DEVICE, 0);
                drm_gem_put_pages(&bo->gem, bo->pages, true, true);
                sg_free_table(bo->sgt);
                kfree(bo->sgt);
@@ -290,12 +288,9 @@ static int tegra_bo_get_pages(struct drm_device *drm, struct tegra_bo *bo)
                goto put_pages;
        }
 
-       err = dma_map_sg(drm->dev, bo->sgt->sgl, bo->sgt->nents,
-                        DMA_FROM_DEVICE);
-       if (err == 0) {
-               err = -EFAULT;
+       err = dma_map_sgtable(drm->dev, bo->sgt, DMA_FROM_DEVICE, 0);
+       if (err)
                goto free_sgt;
-       }
 
        return 0;
 
@@ -571,7 +566,7 @@ tegra_gem_prime_map_dma_buf(struct dma_buf_attachment *attach,
                        goto free;
        }
 
-       if (dma_map_sg(attach->dev, sgt->sgl, sgt->nents, dir) == 0)
+       if (dma_map_sgtable(attach->dev, sgt, dir, 0))
                goto free;
 
        return sgt;
@@ -590,7 +585,7 @@ static void tegra_gem_prime_unmap_dma_buf(struct dma_buf_attachment *attach,
        struct tegra_bo *bo = to_tegra_bo(gem);
 
        if (bo->pages)
-               dma_unmap_sg(attach->dev, sgt->sgl, sgt->nents, dir);
+               dma_unmap_sgtable(attach->dev, sgt, dir, 0);
 
        sg_free_table(sgt);
        kfree(sgt);
@@ -609,8 +604,7 @@ static int tegra_gem_prime_begin_cpu_access(struct dma_buf *buf,
        struct drm_device *drm = gem->dev;
 
        if (bo->pages)
-               dma_sync_sg_for_cpu(drm->dev, bo->sgt->sgl, bo->sgt->nents,
-                                   DMA_FROM_DEVICE);
+               dma_sync_sgtable_for_cpu(drm->dev, bo->sgt, DMA_FROM_DEVICE);
 
        return 0;
 }
@@ -623,8 +617,7 @@ static int tegra_gem_prime_end_cpu_access(struct dma_buf *buf,
        struct drm_device *drm = gem->dev;
 
        if (bo->pages)
-               dma_sync_sg_for_device(drm->dev, bo->sgt->sgl, bo->sgt->nents,
-                                      DMA_TO_DEVICE);
+               dma_sync_sgtable_for_device(drm->dev, bo->sgt, DMA_TO_DEVICE);
 
        return 0;
 }

diff --git a/drivers/gpu/drm/tegra/plane.c b/drivers/gpu/drm/tegra/plane.c
index 4cd0461..539d149 100644 (file)
--- a/drivers/gpu/drm/tegra/plane.c
+++ b/drivers/gpu/drm/tegra/plane.c
@@ -131,12 +131,9 @@ static int tegra_dc_pin(struct tegra_dc *dc, struct tegra_plane_state *state)
                }
 
                if (sgt) {
-                       err = dma_map_sg(dc->dev, sgt->sgl, sgt->nents,
-                                        DMA_TO_DEVICE);
-                       if (err == 0) {
-                               err = -ENOMEM;
+                       err = dma_map_sgtable(dc->dev, sgt, DMA_TO_DEVICE, 0);
+                       if (err)
                                goto unpin;
-                       }
 
                        /*
                         * The display controller needs contiguous memory, so
@@ -144,7 +141,7 @@ static int tegra_dc_pin(struct tegra_dc *dc, struct tegra_plane_state *state)
                         * map its SG table to a single contiguous chunk of
                         * I/O virtual memory.
                         */
-                       if (err > 1) {
+                       if (sgt->nents > 1) {
                                err = -EINVAL;
                                goto unpin;
                        }
@@ -166,8 +163,7 @@ unpin:
                struct sg_table *sgt = state->sgt[i];
 
                if (sgt)
-                       dma_unmap_sg(dc->dev, sgt->sgl, sgt->nents,
-                                    DMA_TO_DEVICE);
+                       dma_unmap_sgtable(dc->dev, sgt, DMA_TO_DEVICE, 0);
 
                host1x_bo_unpin(dc->dev, &bo->base, sgt);
                state->iova[i] = DMA_MAPPING_ERROR;
@@ -186,8 +182,7 @@ static void tegra_dc_unpin(struct tegra_dc *dc, struct tegra_plane_state *state)
                struct sg_table *sgt = state->sgt[i];
 
                if (sgt)
-                       dma_unmap_sg(dc->dev, sgt->sgl, sgt->nents,
-                                    DMA_TO_DEVICE);
+                       dma_unmap_sgtable(dc->dev, sgt, DMA_TO_DEVICE, 0);
 
                host1x_bo_unpin(dc->dev, &bo->base, sgt);
                state->iova[i] = DMA_MAPPING_ERROR;