Re: [PATCH v2] drm: gem_cma_helper.c: Allow importing of contiguous scatterlists with nents > 1

[Noralf Trønnes]

Den 15.11.2017 14.04, skrev Liviu Dudau:

Hi,

On Sat, Nov 11, 2017 at 02:47:35PM +0200, Laurent Pinchart wrote:

Hi Liviu,

Thank you for the patch.

On Friday, 10 November 2017 15:33:10 EET Liviu Dudau wrote:

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.pinch...@ideasonboard.com>
Signed-off-by: Liviu Dudau <liviu.du...@arm.com>
---

Laurent,

Thanks for the review! I would like to ask for one more favour: if you
are OK with this version, can you pull this patch through the drm-misc tree?

I could, but I'd first need to set dim up, and I'm currently abroad with a bad
internet connection and a big deadline for the middle of next week (I know,
lots of excuses), so it's not very convenient for me at this time.

Any other drm-misc maintainers feeling helpful and willing to take this
patch in?

Sure, I can do it this evening.

Noralf.

  Otherwise I can send it through the mali-dp tree if no one
objects.

Best regards,
Liviu

  drivers/gpu/drm/drm_gem_cma_helper.c | 22 ++++++++++++++++++++--
  include/drm/drm_gem_cma_helper.h     |  4 +++-
  2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c
b/drivers/gpu/drm/drm_gem_cma_helper.c index 020e7668dfaba..43b179212052d
100644
--- a/drivers/gpu/drm/drm_gem_cma_helper.c
+++ b/drivers/gpu/drm/drm_gem_cma_helper.c
@@ -482,8 +482,26 @@ 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 58a739bf15f1f..214aa85adc8d5
100644
--- 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 {

--
Regards,

Laurent Pinchart