[PATCH v2 1/2] drm/prime: reject DMA-BUF attach when get_sg_table is missing

[Simon Ser <contact@emersion.fr>]

drm_gem_map_dma_buf() requires drm_gem_object_funcs.get_sg_table
to be implemented, or else WARNs.

Allow drivers to leave this hook unimplemented to implement purely
local DMA-BUFs (ie, DMA-BUFs which cannot be imported anywhere
else but the device which allocated them). In that case, reject
imports to other devices in drm_gem_map_attach().

v2: new patch

Signed-off-by: Simon Ser <contact@emersion.fr>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Tian Tao <tiantao6@hisilicon.com>
Cc: Maxime Ripard <maxime@cerno.tech>
Cc: Christian König <christian.koenig@amd.com>
Cc: Hans de Goede <hdegoede@redhat.com>
---
 drivers/gpu/drm/drm_prime.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index f924b8b4ab6b..ab1d21d63a03 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -544,7 +544,8 @@ int drm_prime_handle_to_fd_ioctl(struct drm_device *dev, void *data,
  * Optional pinning of buffers is handled at dma-buf attach and detach time in
  * drm_gem_map_attach() and drm_gem_map_detach(). Backing storage itself is
  * handled by drm_gem_map_dma_buf() and drm_gem_unmap_dma_buf(), which relies on
- * &drm_gem_object_funcs.get_sg_table.
+ * &drm_gem_object_funcs.get_sg_table. If &drm_gem_object_funcs.get_sg_table is
+ * unimplemented, exports into another device are rejected.
  *
  * For kernel-internal access there's drm_gem_dmabuf_vmap() and
  * drm_gem_dmabuf_vunmap(). Userspace mmap support is provided by
@@ -583,6 +584,9 @@ int drm_gem_map_attach(struct dma_buf *dma_buf,
 {
 	struct drm_gem_object *obj = dma_buf->priv;
 
+	if (!obj->funcs->get_sg_table)
+		return -EOPNOTSUPP;
+
 	return drm_gem_pin(obj);
 }
 EXPORT_SYMBOL(drm_gem_map_attach);
-- 
2.39.2