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

[Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>]

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 <afd@xxxxxx>
> ---

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 */