drm: gem_cma_helper.c: Allow importing of contiguous scatterlists with nents > 1

drm_gem_cma_prime_import_sg_table() will fail if the number of entries
in the sg_table > 1. However, you can have a device that uses an IOMMU
engine and can map a discontiguous buffer with multiple entries that
have consecutive sg_dma_addresses, effectively making it contiguous.
Allow for that scenario by testing the entries in the sg_table for
contiguous coverage.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20171110133310.1225-1-Liviu.Dudau@arm.com

diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c b/drivers/gpu/drm/drm_gem_cma_helper.c
index ce67d7d..80a5115 100644 (file)
--- a/drivers/gpu/drm/drm_gem_cma_helper.c
+++ b/drivers/gpu/drm/drm_gem_cma_helper.c
@@ -475,8 +475,26 @@ drm_gem_cma_prime_import_sg_table(struct drm_device *dev,
 {
        struct drm_gem_cma_object *cma_obj;
 
-       if (sgt->nents != 1)
-               return ERR_PTR(-EINVAL);
+       if (sgt->nents != 1) {
+               /* check if the entries in the sg_table are contiguous */
+               dma_addr_t next_addr = sg_dma_address(sgt->sgl);
+               struct scatterlist *s;
+               unsigned int i;
+
+               for_each_sg(sgt->sgl, s, sgt->nents, i) {
+                       /*
+                        * sg_dma_address(s) is only valid for entries
+                        * that have sg_dma_len(s) != 0
+                        */
+                       if (!sg_dma_len(s))
+                               continue;
+
+                       if (sg_dma_address(s) != next_addr)
+                               return ERR_PTR(-EINVAL);
+
+                       next_addr = sg_dma_address(s) + sg_dma_len(s);
+               }
+       }
 
        /* Create a CMA GEM buffer. */
        cma_obj = __drm_gem_cma_create(dev, attach->dmabuf->size);

diff --git a/include/drm/drm_gem_cma_helper.h b/include/drm/drm_gem_cma_helper.h
index 76ded75..f191227 100644 (file)
--- a/include/drm/drm_gem_cma_helper.h
+++ b/include/drm/drm_gem_cma_helper.h
@@ -8,7 +8,9 @@
  * struct drm_gem_cma_object - GEM object backed by CMA memory allocations
  * @base: base GEM object
  * @paddr: physical address of the backing memory
- * @sgt: scatter/gather table for imported PRIME buffers
+ * @sgt: scatter/gather table for imported PRIME buffers. The table can have
+ *       more than one entry but they are guaranteed to have contiguous
+ *       DMA addresses.
  * @vaddr: kernel virtual address of the backing memory
  */
 struct drm_gem_cma_object {