Re: [PATCH v3] drm: omapdrm: Improve check for contiguous buffers

[Tomi Valkeinen]

On 13/11/2023 22:55, Andrew Davis wrote:

While a scatter-gather table having only 1 entry does imply it is
contiguous, it is a logic error to assume the inverse. Tables can have
more than 1 entry and still be contiguous. Use a proper check here.

Signed-off-by: Andrew Davis <a...@ti.com>
---

Thanks, I'll pick this up.

 Tomi

Changes from v2:
  - Double check that these multi-segment SGTs are handled correctly elsewhere 
in the driver
  - Rebase on v6.7-rc1

Changes from v1:
  - Sent correct version of patch :)

  drivers/gpu/drm/omapdrm/omap_gem.c | 14 ++++++++++----
  1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/omapdrm/omap_gem.c 
b/drivers/gpu/drm/omapdrm/omap_gem.c
index c48fa531ca321..3421e8389222a 100644
--- a/drivers/gpu/drm/omapdrm/omap_gem.c
+++ b/drivers/gpu/drm/omapdrm/omap_gem.c
@@ -48,7 +48,7 @@ struct omap_gem_object {
         *   OMAP_BO_MEM_DMA_API flag set)
         *
         * - buffers imported from dmabuf (with the OMAP_BO_MEM_DMABUF flag set)
-        *   if they are physically contiguous (when sgt->orig_nents == 1)
+        *   if they are physically contiguous
         *
         * - buffers mapped through the TILER when pin_cnt is not zero, in which
         *   case the DMA address points to the TILER aperture
@@ -148,12 +148,18 @@ u64 omap_gem_mmap_offset(struct drm_gem_object *obj)
        return drm_vma_node_offset_addr(&obj->vma_node);
  }

+static bool omap_gem_sgt_is_contiguous(struct sg_table *sgt, size_t size)

+{
+       return !(drm_prime_get_contiguous_size(sgt) < size);
+}
+
  static bool omap_gem_is_contiguous(struct omap_gem_object *omap_obj)
  {
        if (omap_obj->flags & OMAP_BO_MEM_DMA_API)
                return true;

- if ((omap_obj->flags & OMAP_BO_MEM_DMABUF) && omap_obj->sgt->nents == 1)

+       if ((omap_obj->flags & OMAP_BO_MEM_DMABUF) &&
+           omap_gem_sgt_is_contiguous(omap_obj->sgt, omap_obj->base.size))
                return true;

return false;

@@ -1385,7 +1391,7 @@ struct drm_gem_object *omap_gem_new_dmabuf(struct 
drm_device *dev, size_t size,
        union omap_gem_size gsize;

/* Without a DMM only physically contiguous buffers can be supported. */

-       if (sgt->orig_nents != 1 && !priv->has_dmm)
+       if (!omap_gem_sgt_is_contiguous(sgt, size) && !priv->has_dmm)
                return ERR_PTR(-EINVAL);

gsize.bytes = PAGE_ALIGN(size);

@@ -1399,7 +1405,7 @@ struct drm_gem_object *omap_gem_new_dmabuf(struct 
drm_device *dev, size_t size,

omap_obj->sgt = sgt; - if (sgt->orig_nents == 1) {

+       if (omap_gem_sgt_is_contiguous(sgt, size)) {
                omap_obj->dma_addr = sg_dma_address(sgt->sgl);
        } else {
                /* Create pages list from sgt */