Am 19.10.21 um 16:30 schrieb Daniel Vetter:
On Tue, Oct 19, 2021 at 03:02:26PM +0200, Christian König wrote:
Am 13.10.21 um 16:23 schrieb Daniel Vetter:
On Tue, Oct 05, 2021 at 01:37:38PM +0200, Christian König wrote:
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@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..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.
Yeah that's another issue, but in practice there's no libva which decodes
into planar yuv with different fences between the planes. So not a bug in
practice.
But this is entirely orthogonal to you picking up the wrong fence here if
there's not exclusive fence set:
- old code: Either pick the exclusive fence, or not fence if the exclusive
one is not set.
- new code: Pick the exclusive fence or the first shared fence
Hui what?
We use "dma_resv_iter_begin(&cursor, obj->resv, *false*);" here which
means that only the exclusive fence is returned and no shared fences
whatsoever.
My next step is to replace the boolean with a bunch of use case
describing enums. I hope that will make it much clearer what's going on
here.
Christian.
New behaviour is busted, because scanning out and reading from a buffer at
the same time (for the next frame, e.g. to copy over damaged areas or some
other tricks) is very much a supported thing. Atomic _only_ wants to look
at the exclusive fence slot, which mean "there is an implicitly synced
write to this buffers". Implicitly synced reads _must_ be ignored.
Now amdgpu doesn't have this distinction in its uapi, but many drivers do.
-Daniel
Support for more than one write fence then comes totally naturally.
Christian.
-Daniel
+ 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
