drm: i915: 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.

This driver creatively uses sg_table->orig_nents to store the size of the
allocated scatterlist and ignores the number of the entries returned by
dma_map_sg function. The sg_table->orig_nents is (mis)used to properly
free the (over)allocated scatterlist.

This patch only introduces the common DMA-mapping wrappers operating
directly on the struct sg_table objects to the dmabuf related functions,
so the other drivers, which might share buffers with i915 could rely on
the properly set nents and orig_nents values.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Michael J. Ruhl <michael.j.ruhl@intel.com>

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
index 2679380..8a98859 100644 (file)
--- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
@@ -48,12 +48,9 @@ static struct sg_table *i915_gem_map_dma_buf(struct dma_buf_attachment *attachme
                src = sg_next(src);
        }
 
-       if (!dma_map_sg_attrs(attachment->dev,
-                             st->sgl, st->nents, dir,
-                             DMA_ATTR_SKIP_CPU_SYNC)) {
-               ret = -ENOMEM;
+       ret = dma_map_sgtable(attachment->dev, st, dir, DMA_ATTR_SKIP_CPU_SYNC);
+       if (ret)
                goto err_free_sg;
-       }
 
        return st;
 
@@ -73,9 +70,7 @@ static void i915_gem_unmap_dma_buf(struct dma_buf_attachment *attachment,
 {
        struct drm_i915_gem_object *obj = dma_buf_to_obj(attachment->dmabuf);
 
-       dma_unmap_sg_attrs(attachment->dev,
-                          sg->sgl, sg->nents, dir,
-                          DMA_ATTR_SKIP_CPU_SYNC);
+       dma_unmap_sgtable(attachment->dev, sg, dir, DMA_ATTR_SKIP_CPU_SYNC);
        sg_free_table(sg);
        kfree(sg);
 

diff --git a/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c b/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
index debaf7b..be30b27 100644 (file)
--- a/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
+++ b/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
@@ -28,10 +28,9 @@ static struct sg_table *mock_map_dma_buf(struct dma_buf_attachment *attachment,
                sg = sg_next(sg);
        }
 
-       if (!dma_map_sg(attachment->dev, st->sgl, st->nents, dir)) {
-               err = -ENOMEM;
+       err = dma_map_sgtable(attachment->dev, st, dir, 0);
+       if (err)
                goto err_st;
-       }
 
        return st;
 
@@ -46,7 +45,7 @@ static void mock_unmap_dma_buf(struct dma_buf_attachment *attachment,
                               struct sg_table *st,
                               enum dma_data_direction dir)
 {
-       dma_unmap_sg(attachment->dev, st->sgl, st->nents, dir);
+       dma_unmap_sgtable(attachment->dev, st, dir, 0);
        sg_free_table(st);
        kfree(st);
 }