[PATCH v2] drm: omapdrm: Improve check for contiguous buffers

[PATCH v2] drm: omapdrm: Improve check for contiguous buffers

[Andrew Davis]

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 <afd@ti.com>
---

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 cf571796fd26e..c10f3d2dd61ce 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;
@@ -1398,7 +1404,7 @@ 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);
@@ -1412,7 +1418,7 @@ 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 */
-- 
2.36.1

Re: [PATCH v2] drm: omapdrm: Improve check for contiguous buffers

[Tomi Valkeinen]

On 25/08/2022 19:26, 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 <afd@ti.com>
> ---
> 
> Changes from v1:
>   - Sent correct version of patch :)

Looks fine to me. But where do you need this? Are contiguous buffers 
with multiple sgt entries handled correctly elsewhere in the driver, 
i.e. do they work? =)

  Tomi