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, 122 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 23e4661a62fe..4f6e52961951 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -795,6 +795,9 @@ int drm_atomic_helper_check(struct drm_device *dev,
 	if (ret)
 		return ret;
 
+	if (state->legacy_cursor_update)
+		state->async_update = !drm_atomic_helper_async_check(dev, state);
+
 	return ret;
 }
 EXPORT_SYMBOL(drm_atomic_helper_check);
@@ -1353,6 +1356,114 @@ static void commit_work(struct work_struct *work)
 }
 
 /**
+ * drm_atomic_helper_async_check - check if state can be commited asynchronously
+ * @dev: DRM device
+ * @state: the driver state object
+ *
+ * This helper will check if it is possible to commit the state asynchronously.
+ * Async commits are not supposed to swap the states like normal sync commits
+ * but just do in-place changes on the current state.
+ *
+ * It will return 0 if the commit can happen in an asynchronous fashion or error
+ * if not. Note that error just mean it can't be commited asynchronously, if it
+ * fails the commit should be treated like a normal synchronous commit.
+ */
+int drm_atomic_helper_async_check(struct drm_device *dev,
+				   struct drm_atomic_state *state)
+{
+	struct drm_crtc *crtc;
+	struct drm_crtc_state *crtc_state;
+	struct drm_crtc_commit *commit;
+	struct drm_plane *__plane, *plane = NULL;
+	struct drm_plane_state *__plane_state, *plane_state = NULL;
+	const struct drm_plane_helper_funcs *funcs;
+	int i, j, n_planes = 0;
+
+	for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
+		if (drm_atomic_crtc_needs_modeset(crtc_state))
+			return -EINVAL;
+	}
+
+	for_each_new_plane_in_state(state, __plane, __plane_state, i) {
+		n_planes++;
+		plane = __plane;
+		plane_state = __plane_state;
+	}
+
+	/* FIXME: we support only single plane updates for now */
+	if (!plane || n_planes != 1)
+		return -EINVAL;
+
+	if (!plane_state->crtc)
+		return -EINVAL;
+
+	funcs = plane->helper_private;
+	if (!funcs->atomic_async_update)
+		return -EINVAL;
+
+	if (plane_state->fence)
+		return -EINVAL;
+
+	/*
+	 * Don't do an async update if there is an outstanding commit modifying
+	 * the plane.  This prevents our async update's changes from getting
+	 * overridden by a previous synchronous update's state.
+	 */
+	for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
+		if (plane->crtc != crtc)
+			continue;
+
+		spin_lock(&crtc->commit_lock);
+		commit = list_first_entry_or_null(&crtc->commit_list,
+						  struct drm_crtc_commit,
+						  commit_entry);
+		if (!commit) {
+			spin_unlock(&crtc->commit_lock);
+			continue;
+		}
+		spin_unlock(&crtc->commit_lock);
+
+		if (!crtc->state->state)
+			continue;
+
+		for_each_plane_in_state(crtc->state->state, __plane,
+					__plane_state, j) {
+			if (__plane == plane)
+				return -EINVAL;
+		}
+	}
+
+	return funcs->atomic_async_check(plane, plane_state);
+}
+EXPORT_SYMBOL(drm_atomic_helper_async_check);
+
+/**
+ * drm_atomic_helper_async_commit - commit state asynchronously
+ * @dev: DRM device
+ * @state: the driver state object
+ *
+ * This function commits a state asynchronously, i.e., not vblank
+ * synchronized. It should be used on a state only when
+ * drm_atomic_async_check() succeeds. Async commits are not supposed to swap
+ * the states like normal sync commits, but just do in-place changes on the
+ * current state.
+ */
+void drm_atomic_helper_async_commit(struct drm_device *dev,
+				    struct drm_atomic_state *state)
+{
+	struct drm_plane *plane;
+	struct drm_plane_state *plane_state;
+	const struct drm_plane_helper_funcs *funcs;
+	int i;
+
+	for_each_new_plane_in_state(state, plane, plane_state, i) {
+		funcs = plane->helper_private;
+		funcs->atomic_async_update(plane, plane_state);
+	}
+}
+EXPORT_SYMBOL(drm_atomic_helper_async_commit);
+
+/**
  * drm_atomic_helper_commit - commit validated state object
  * @dev: DRM device
  * @state: the driver state object
@@ -1376,6 +1487,17 @@ int drm_atomic_helper_commit(struct drm_device *dev,
 {
 	int ret;
 
+	if (state->async_update) {
+		ret = drm_atomic_helper_prepare_planes(dev, state);
+		if (ret)
+			return ret;
+
+		drm_atomic_helper_async_commit(dev, state);
+		drm_atomic_helper_cleanup_planes(dev, state);
+
+		return 0;
+	}
+
 	ret = drm_atomic_helper_setup_commit(state, nonblock);
 	if (ret)
 		return ret;