Re: [PATCH 24/28] drm: use new iterator in drm_gem_plane_helper_prepare_fb

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Am 05.10.21 um 09:53 schrieb Tvrtko Ursulin:

On 01/10/2021 11:06, Christian König wrote:
Makes the handling a bit more complex, but avoids the use of
dma_resv_get_excl_unlocked().

Signed-off-by: Christian König <christian.koenig@xxxxxxx>
---
  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..21ed930042b8 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) {
+        dma_fence_get(fence);
+        dma_resv_iter_end(&cursor);
+        /* TODO: We only use the first write fence here */

What is the TODO? NB instead?

The drm atomic API can unfortunately handle only one fence and we can certainly have more than that.


+ drm_atomic_set_fence_for_plane(state, fence);
+        return 0;
+    }
+    dma_resv_iter_end(&cursor);
  +    drm_atomic_set_fence_for_plane(state, NULL);

    dma_resv_iter_begin(&cursor, obj->resv, false);
    dma_resv_for_each_fence_unlocked(&cursor, fence) {
        dma_fence_get(fence);
        break;
    }
    dma_resv_iter_end(&cursor);

    drm_atomic_set_fence_for_plane(state, fence);

Does this work?

Yeah that should work as well.


But overall I am not sure this is nicer. Is the goal to remove dma_resv_get_excl_unlocked as API it just does not happen in this series?

Yes, the only user left is the i915_gem_object_last_write_engine() function and that one you already removed in i915.

Regards,
Christian.


Regards,

Tvrtko

      return 0;
  }
  EXPORT_SYMBOL_GPL(drm_gem_plane_helper_prepare_fb);





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