Am 13.10.21 um 16:23 schrieb Daniel Vetter:

On Tue, Oct 05, 2021 at 01:37:38PM +0200, Christian König wrote:

quoted

Makes the handling a bit more complex, but avoids the use of
dma_resv_get_excl_unlocked().

v2: improve coding and documentation

Signed-off-by: Christian König <christian.koenig@amd.com>
---
  drivers/gpu/drm/drm_gem_atomic_helper.c | 13 +++++++++++--
  1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_atomic_helper.c b/drivers/gpu/drm/drm_gem_atomic_helper.c
index e570398abd78..8534f78d4d6d 100644
--- a/drivers/gpu/drm/drm_gem_atomic_helper.c
+++ b/drivers/gpu/drm/drm_gem_atomic_helper.c

@@ -143,6 +143,7 @@
   */
  int drm_gem_plane_helper_prepare_fb(struct drm_plane *plane, struct drm_plane_state *state)
  {
+	struct dma_resv_iter cursor;
  	struct drm_gem_object *obj;
  	struct dma_fence *fence;
  

@@ -150,9 +151,17 @@ int drm_gem_plane_helper_prepare_fb(struct drm_plane *plane, struct drm_plane_st
  		return 0;
  
  	obj = drm_gem_fb_get_obj(state->fb, 0);
-	fence = dma_resv_get_excl_unlocked(obj->resv);
-	drm_atomic_set_fence_for_plane(state, fence);
+	dma_resv_iter_begin(&cursor, obj->resv, false);
+	dma_resv_for_each_fence_unlocked(&cursor, fence) {
+		/* TODO: We only use the first write fence here and need to fix
+		 * the drm_atomic_set_fence_for_plane() API to accept more than
+		 * one. */

I'm confused, right now there is only one write fence. So no need to
iterate, and also no need to add a TODO. If/when we add more write fences
then I think this needs to be revisited, and ofc then we do need to update
the set_fence helpers to carry an entire array of fences.

Well could be that I misunderstood you, but in your last explanation it 
sounded like the drm_atomic_set_fence_for_plane() function needs fixing 
anyway because a plane could have multiple BOs.

So in my understanding what we need is a 
drm_atomic_add_dependency_for_plane() function which records that a 
certain fence needs to be signaled before a flip.

Support for more than one write fence then comes totally naturally.

Christian.

-Daniel

quoted

+		dma_fence_get(fence);
+		break;
+	}
+	dma_resv_iter_end(&cursor);
  
+	drm_atomic_set_fence_for_plane(state, fence);
  	return 0;
  }
  EXPORT_SYMBOL_GPL(drm_gem_plane_helper_prepare_fb);
-- 
2.25.1