drm: handle kernel fences in drm_gem_plane_helper_prepare_fb v2

drm_gem_plane_helper_prepare_fb() was using
drm_atomic_set_fence_for_plane() which ignores all implicit fences when an
explicit fence is already set. That's rather unfortunate when the fb still
has a kernel fence we need to wait for to avoid presenting garbage on the
screen.

So instead update the fence in the plane state directly. While at it also
take care of all potential GEM objects and not just the first one.

Also remove the now unused drm_atomic_set_fence_for_plane() function, new
drivers should probably use the atomic helpers directly.

v2: improve kerneldoc, use local variable and num_planes, WARN_ON_ONCE
    on missing planes.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> (v1)
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220429134230.24334-1-christian.koenig@amd.com

1 files changed, 5 insertions, 42 deletions

diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
index c6394ba13b24..434f3d4cb8a2 100644
--- a/drivers/gpu/drm/drm_atomic_uapi.c
+++ b/drivers/gpu/drm/drm_atomic_uapi.c
@@ -255,43 +255,6 @@ drm_atomic_set_fb_for_plane(struct drm_plane_state *plane_state,
 EXPORT_SYMBOL(drm_atomic_set_fb_for_plane);
 
 /**
- * drm_atomic_set_fence_for_plane - set fence for plane
- * @plane_state: atomic state object for the plane
- * @fence: dma_fence to use for the plane
- *
- * Helper to setup the plane_state fence in case it is not set yet.
- * By using this drivers doesn't need to worry if the user choose
- * implicit or explicit fencing.
- *
- * This function will not set the fence to the state if it was set
- * via explicit fencing interfaces on the atomic ioctl. In that case it will
- * drop the reference to the fence as we are not storing it anywhere.
- * Otherwise, if &drm_plane_state.fence is not set this function we just set it
- * with the received implicit fence. In both cases this function consumes a
- * reference for @fence.
- *
- * This way explicit fencing can be used to overrule implicit fencing, which is
- * important to make explicit fencing use-cases work: One example is using one
- * buffer for 2 screens with different refresh rates. Implicit fencing will
- * clamp rendering to the refresh rate of the slower screen, whereas explicit
- * fence allows 2 independent render and display loops on a single buffer. If a
- * driver allows obeys both implicit and explicit fences for plane updates, then
- * it will break all the benefits of explicit fencing.
- */
-void
-drm_atomic_set_fence_for_plane(struct drm_plane_state *plane_state,
-			       struct dma_fence *fence)
-{
-	if (plane_state->fence) {
-		dma_fence_put(fence);
-		return;
-	}
-
-	plane_state->fence = fence;
-}
-EXPORT_SYMBOL(drm_atomic_set_fence_for_plane);
-
-/**
  * drm_atomic_set_crtc_for_connector - set CRTC for connector
  * @conn_state: atomic state object for the connector
  * @crtc: CRTC to use for the connector
@@ -1077,10 +1040,10 @@ int drm_atomic_set_property(struct drm_atomic_state *state,
  *
  * As a contrast, with implicit fencing the kernel keeps track of any
  * ongoing rendering, and automatically ensures that the atomic update waits
- * for any pending rendering to complete. For shared buffers represented with
- * a &struct dma_buf this is tracked in &struct dma_resv.
- * Implicit syncing is how Linux traditionally worked (e.g. DRI2/3 on X.org),
- * whereas explicit fencing is what Android wants.
+ * for any pending rendering to complete. This is usually tracked in &struct
+ * dma_resv which can also contain mandatory kernel fences. Implicit syncing
+ * is how Linux traditionally worked (e.g. DRI2/3 on X.org), whereas explicit
+ * fencing is what Android wants.
  *
  * "IN_FENCE_FD”:
  *	Use this property to pass a fence that DRM should wait on before
@@ -1095,7 +1058,7 @@ int drm_atomic_set_property(struct drm_atomic_state *state,
  *
  *	On the driver side the fence is stored on the @fence parameter of
  *	&struct drm_plane_state. Drivers which also support implicit fencing
- *	should set the implicit fence using drm_atomic_set_fence_for_plane(),
+ *	should extract the implicit fence using drm_gem_plane_helper_prepare_fb(),
  *	to make sure there's consistent behaviour between drivers in precedence
  *	of implicit vs. explicit fencing.
  *