drm/crtc: Add a generic infrastructure to fake VBLANK events

In some cases CRTCs are active but are not able to generating events, at
least not at every frame at it's expected to.
This is typically the case when the CRTC is feeding a writeback connector
that has no job queued. In this situation the CRTC is usually stopped
until a new job is queued, and this can lead to timeouts when part of
the pipeline is updated but no new jobs are queued to the active
writeback connector.

In order to solve that, we add a ->no_vblank flag to drm_crtc_state
and ask the CRTC drivers to set it to true when they know they're not
able to generate VBLANK events. The core drm_atomic_helper_fake_vblank()
helper can then be used to fake VBLANKs at commit time.

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180703075022.15138-6-boris.brezillon@bootlin.com

1 files changed, 1 insertions, 0 deletions

diff --git a/include/drm/drm_atomic_helper.h b/include/drm/drm_atomic_helper.h
index 26aaba58d6ce..99e2a5297c69 100644
--- a/include/drm/drm_atomic_helper.h
+++ b/include/drm/drm_atomic_helper.h
@@ -100,6 +100,7 @@ int __must_check drm_atomic_helper_swap_state(struct drm_atomic_state *state,
 int drm_atomic_helper_setup_commit(struct drm_atomic_state *state,
 				   bool nonblock);
 void drm_atomic_helper_wait_for_dependencies(struct drm_atomic_state *state);
+void drm_atomic_helper_fake_vblank(struct drm_atomic_state *state);
 void drm_atomic_helper_commit_hw_done(struct drm_atomic_state *state);
 void drm_atomic_helper_commit_cleanup_done(struct drm_atomic_state *state);