drm/atomic: initial support for asynchronous plane update

In some cases, like cursor updates, it is interesting to update the
plane in an asynchronous fashion to avoid big delays. The current queued
update could be still waiting for a fence to signal and thus block any
subsequent update until its scan out. In cases like this if we update the
cursor synchronously through the atomic API it will cause significant
delays that would even be noticed by the final user.

This patch creates a fast path to jump ahead the current queued state and
do single planes updates without going through all atomic steps in
drm_atomic_helper_commit(). We take this path for legacy cursor updates.

For now only single plane updates are supported, but we plan to support
multiple planes updates and async PageFlips through this interface as well
in the near future.

v6:	- move check code to drm_atomic_helper.c (Daniel Vetter)

v5:
	- improve comments (Eric Anholt)

v4:
	- fix state->crtc NULL check (Archit Taneja)

v3:
	- fix iteration on the wrong crtc state
	- put back code to forbid updates if there is a queued update for
	the same plane (Ville Syrjälä)
	- move size checks back to drivers (Ville Syrjälä)
	- move ASYNC_UPDATE flag addition to its own patch (Ville Syrjälä)

v2:
	- allow updates even if there is a queued update for the same
	plane.
        - fixes on the documentation (Emil Velikov)
        - unconditionally call ->atomic_async_update (Emil Velikov)
        - check for ->atomic_async_update earlier (Daniel Vetter)
        - make ->atomic_async_check() the last step (Daniel Vetter)
        - add ASYNC_UPDATE flag (Eric Anholt)
        - update state in core after ->atomic_async_update (Eric Anholt)
	- update docs (Eric Anholt)

Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Eric Anholt <eric@anholt.net>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Reviewed-by: Archit Taneja <architt@codeaurora.org> (v5)
Acked-by: Eric Anholt <eric@anholt.net> (v5)
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20170630180322.29007-2-gustavo@padovan.org

1 files changed, 2 insertions, 0 deletions

diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
index 0196f264a418..dcc8e0cdb7ff 100644
--- a/include/drm/drm_atomic.h
+++ b/include/drm/drm_atomic.h
@@ -207,6 +207,7 @@ struct __drm_private_objs_state {
  * @dev: parent DRM device
  * @allow_modeset: allow full modeset
  * @legacy_cursor_update: hint to enforce legacy cursor IOCTL semantics
+ * @async_update: hint for asynchronous plane update
  * @planes: pointer to array of structures with per-plane data
  * @crtcs: pointer to array of CRTC pointers
  * @num_connector: size of the @connectors and @connector_states arrays
@@ -221,6 +222,7 @@ struct drm_atomic_state {
 	struct drm_device *dev;
 	bool allow_modeset : 1;
 	bool legacy_cursor_update : 1;
+	bool async_update : 1;
 	struct __drm_planes_state *planes;
 	struct __drm_crtcs_state *crtcs;
 	int num_connector;