drm: Atomic crtc/connector updates using crtc/plane helper interfaces

So this is finally the integration of the crtc and plane helper
interfaces into the atomic helper functions.

In the check function we now have a few steps:

- First we update the output routing and figure out which crtcs need a
  full mode set. Suitable encoders are selected using ->best_encoder,
  with the same semantics as the crtc helpers of implicitly disabling
  all connectors currently using the encoder.

- Then we pull all other connectors into the state update which feed
  from a crtc which changes. This must be done do catch mode changes
  and similar updates - atomic updates are differences on top of the
  current state.

- Then we call all the various ->mode_fixup to compute the adjusted
  mode. Note that here we have a slight semantic difference compared
  to the crtc helpers: We have not yet updated the encoder->crtc link
  when calling the encoder's ->mode_fixup function. But that's a
  requirement when converting to atomic since we want to prepare the
  entire state completely contained with the over drm_atomic_state
  structure. So this must be carefully checked when converting drivers
  over to atomic helpers.

- Finally we do call the atomic_check functions on planes and crtcs.

The commit function is also quite a beast:

- The only step that can fail is done first, namely pinning the
  framebuffers. After that we cross the point of no return, an async
  commit would push all that into the worker thread.

- The disabling of encoders and connectors is a bit tricky, since
  depending upon the final state we need to select different crtc
  helper functions.

- Software tracking is a bit clarified compared to the crtc helpers:
  We commit the software state before starting to touch the hardware,
  like crtc helpers. But since we just swap them we still have the old
  state (i.e. the current hw state) around, which is really handy to
  write simple disable functions. So no more
  drm_crtc_helper_disable_all_unused_functions kind of fun because
  we're leaving unused crtcs/encoders behind. Everything gets shut
  down in-order now, which is one of the key differences of the i915
  helpers compared to crtc helpers and a really nice additional
  guarantee.

- Like with the plane helpers the atomic commit function waits for one
  vblank to pass before calling the framebuffer cleanup function.

Compared to Rob's helper approach there's a bunch of upsides:

- All the interfaces which can fail are called in the ->check hook
  (i.e. ->best_match and the various ->mode_fixup hooks). This means
  that drivers can just reuse those functions and don't need to move
  everything into ->atomic_check callbacks. If drivers have no need
  for additional constraint checking beyong their existing crtc
  helper callbacks they don't need to do anything.

- The actual commit operation is properly stage: First we prepare
  framebuffers, which can potentially still fail (due to memory
  exhausting). This is important for the async case, where this must
  be done synchronously to correctly return errors.

- The output configuration changes (done with crtc helper functions)
  and the plane update (using atomic plane helpers) are correctly
  interleaved: First we shut down any crtcs that need changing, then
  we update planes and finally we enable everything again. Hardware
  without GO bits must be more careful with ordering, which this
  sequence enables.

- Also for hardware with shared output resources (like display PLLs)
  we first must shut down the old configuration before we can enable
  the new one. Otherwise we can hit an impossible intermediate state
  where there's not enough PLLs (which is the point behind atomic
  updates).

v2:
- Ensure that users of ->check update crtc_state->enable correctly.
- Update the legacy state in crtc/plane structures. Eventually we want
  to remove that, but for now the drm core still expects this (especially
  the plane->fb pointer).

v3: A few changes for better async handling:

- Reorder the software side state commit so that it happens all before
  we touch the hardware. This way async support becomes very easy
  since we can punt all the actual hw touching to a worker thread. And
  as long as we synchronize with that thread (flushing or cancelling,
  depending upon what the driver can handle) before we commit the next
  software state there's no need for any locking in the worker thread
  at all. Which greatly simplifies things.

  And as long as we synchronize with all relevant threads we can have
  a lot of them (e.g. per-crtc for per-crtc updates) running in
  parallel.

- Expose pre/post plane commit steps separately. We need to expose the
  actual hw commit step anyway for drivers to be able to implement
  asynchronous commit workers. But if we expose pre/post and plane
  commit steps individually we allow drivers to selectively use atomic
  helpers.

- I've forgotten to call encoder/bridge ->mode_set functions, fix
  this.

v4: Add debug output and fix a mixup between current and new state
that resulted in crtcs not getting updated correctly. And in an
Oops ...

v5:
- Be kind to driver writers in the vblank wait functions.. if thing
  aren't working yet, and vblank irq will never come, then let's not
  block forever.. especially under console-lock.
- Correctly clear connector_state->best_encoder when disabling.
  Spotted while trying to understand a report from Rob Clark.
- Only steal encoder if it actually changed, otherwise hilarity ensues
  if we steal from the current connector and so set the ->crtc pointer
  unexpectedly to NULL. Reported by Rob Clark.
- Bail out in disable_outputs if an output currently doesn't have a
  best_encoder - this means it's already disabled.

v6: Fixupe kerneldoc as reported by Paulo. And also fix up kerneldoc
in drm_crtc.h.

v7: Take ownership of the atomic state and clean it up with
drm_atomic_state_free().

v8 Various improvements all over:
- Polish code comments and kerneldoc.
- Improve debug output to make sure all failure cases are logged.
- Treat enabled crtc with no connectors as invalid input from userspace.
- Don't ignore the return value from mode_fixup().

v9:
- Improve debug output for crtc_state->mode_changed.

v10:
- Fixup the vblank waiting code to properly balance the vblank_get/put
  calls.
- Better comments when checking/computing crtc->mode_changed

v11: Fixup the encoder stealing logic: We can't look at encoder->crtc
since that's not in the atomic state structures and might be updated
asynchronously in and async commit. Instead we need to inspect all the
connector states and check whether the encoder is currently in used
and if so, on which crtc.

v12: Review from Sean:
- A few spelling fixes.
- Flatten control flow indent by converting if blocks to early
  continue/return in 2 places.
- Capture connectors_for_crtc return value in int num_connectors
  instead of bool has_connectors and do an explicit int->bool
  conversion with !!. I think the helper is more useful for drivers if
  it returns the number of connectors (e.g. to detect cloning
  configurations), so decided to keep that return value.

Cc: Sean Paul <seanpaul@chromium.org>
Cc: Paulo Zanoni <przanoni@gmail.com>
Cc: Rob Clark <robdclark@gmail.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

4 files changed, 716 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 55a8eb2..c4936bc 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -29,6 +29,7 @@
 #include <drm/drm_atomic.h>
 #include <drm/drm_plane_helper.h>
 #include <drm/drm_crtc_helper.h>
+#include <drm/drm_atomic_helper.h>
 
 static void
 drm_atomic_helper_plane_changed(struct drm_atomic_state *state,
@@ -57,6 +58,332 @@ drm_atomic_helper_plane_changed(struct drm_atomic_state *state,
 	}
 }
 
+static struct drm_crtc *
+get_current_crtc_for_encoder(struct drm_device *dev,
+			     struct drm_encoder *encoder)
+{
+	struct drm_mode_config *config = &dev->mode_config;
+	struct drm_connector *connector;
+
+	WARN_ON(!drm_modeset_is_locked(&config->connection_mutex));
+
+	list_for_each_entry(connector, &config->connector_list, head) {
+		if (connector->state->best_encoder != encoder)
+			continue;
+
+		return connector->state->crtc;
+	}
+
+	return NULL;
+}
+
+static int
+steal_encoder(struct drm_atomic_state *state,
+	      struct drm_encoder *encoder,
+	      struct drm_crtc *encoder_crtc)
+{
+	struct drm_mode_config *config = &state->dev->mode_config;
+	struct drm_crtc_state *crtc_state;
+	struct drm_connector *connector;
+	struct drm_connector_state *connector_state;
+
+	/*
+	 * We can only steal an encoder coming from a connector, which means we
+	 * must already hold the connection_mutex.
+	 */
+	WARN_ON(!drm_modeset_is_locked(&config->connection_mutex));
+
+	DRM_DEBUG_KMS("[ENCODER:%d:%s] in use on [CRTC:%d], stealing it\n",
+		      encoder->base.id, encoder->name,
+		      encoder_crtc->base.id);
+
+	crtc_state = drm_atomic_get_crtc_state(state, encoder_crtc);
+	if (IS_ERR(crtc_state))
+		return PTR_ERR(crtc_state);
+
+	crtc_state->mode_changed = true;
+
+	list_for_each_entry(connector, &config->connector_list, head) {
+		if (connector->state->best_encoder != encoder)
+			continue;
+
+		DRM_DEBUG_KMS("Stealing encoder from [CONNECTOR:%d:%s]\n",
+			      connector->base.id,
+			      connector->name);
+
+		connector_state = drm_atomic_get_connector_state(state,
+								 connector);
+		if (IS_ERR(connector_state))
+			return PTR_ERR(connector_state);
+
+		connector_state->crtc = NULL;
+		connector_state->best_encoder = NULL;
+	}
+
+	return 0;
+}
+
+static int
+update_connector_routing(struct drm_atomic_state *state, int conn_idx)
+{
+	struct drm_connector_helper_funcs *funcs;
+	struct drm_encoder *new_encoder;
+	struct drm_crtc *encoder_crtc;
+	struct drm_connector *connector;
+	struct drm_connector_state *connector_state;
+	struct drm_crtc_state *crtc_state;
+	int idx, ret;
+
+	connector = state->connectors[conn_idx];
+	connector_state = state->connector_states[conn_idx];
+
+	if (!connector)
+		return 0;
+
+	DRM_DEBUG_KMS("Updating routing for [CONNECTOR:%d:%s]\n",
+			connector->base.id,
+			connector->name);
+
+	if (connector->state->crtc != connector_state->crtc) {
+		if (connector->state->crtc) {
+			idx = drm_crtc_index(connector->state->crtc);
+
+			crtc_state = state->crtc_states[idx];
+			crtc_state->mode_changed = true;
+		}
+
+		if (connector_state->crtc) {
+			idx = drm_crtc_index(connector_state->crtc);
+
+			crtc_state = state->crtc_states[idx];
+			crtc_state->mode_changed = true;
+		}
+	}
+
+	if (!connector_state->crtc) {
+		DRM_DEBUG_KMS("Disabling [CONNECTOR:%d:%s]\n",
+				connector->base.id,
+				connector->name);
+
+		connector_state->best_encoder = NULL;
+
+		return 0;
+	}
+
+	funcs = connector->helper_private;
+	new_encoder = funcs->best_encoder(connector);
+
+	if (!new_encoder) {
+		DRM_DEBUG_KMS("No suitable encoder found for [CONNECTOR:%d:%s]\n",
+			      connector->base.id,
+			      connector->name);
+		return -EINVAL;
+	}
+
+	if (new_encoder == connector_state->best_encoder) {
+		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] keeps [ENCODER:%d:%s], now on [CRTC:%d]\n",
+			      connector->base.id,
+			      connector->name,
+			      new_encoder->base.id,
+			      new_encoder->name,
+			      connector_state->crtc->base.id);
+
+		return 0;
+	}
+
+	encoder_crtc = get_current_crtc_for_encoder(state->dev,
+						    new_encoder);
+
+	if (encoder_crtc) {
+		ret = steal_encoder(state, new_encoder, encoder_crtc);
+		if (ret) {
+			DRM_DEBUG_KMS("Encoder stealing failed for [CONNECTOR:%d:%s]\n",
+				      connector->base.id,
+				      connector->name);
+			return ret;
+		}
+	}
+
+	connector_state->best_encoder = new_encoder;
+	idx = drm_crtc_index(connector_state->crtc);
+
+	crtc_state = state->crtc_states[idx];
+	crtc_state->mode_changed = true;
+
+	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] using [ENCODER:%d:%s] on [CRTC:%d]\n",
+		      connector->base.id,
+		      connector->name,
+		      new_encoder->base.id,
+		      new_encoder->name,
+		      connector_state->crtc->base.id);
+
+	return 0;
+}
+
+static int
+mode_fixup(struct drm_atomic_state *state)
+{
+	int ncrtcs = state->dev->mode_config.num_crtc;
+	int nconnectors = state->dev->mode_config.num_connector;
+	struct drm_crtc_state *crtc_state;
+	struct drm_connector_state *conn_state;
+	int i;
+	bool ret;
+
+	for (i = 0; i < ncrtcs; i++) {
+		crtc_state = state->crtc_states[i];
+
+		if (!crtc_state || !crtc_state->mode_changed)
+			continue;
+
+		drm_mode_copy(&crtc_state->adjusted_mode, &crtc_state->mode);
+	}
+
+	for (i = 0; i < nconnectors; i++) {
+		struct drm_encoder_helper_funcs *funcs;
+		struct drm_encoder *encoder;
+
+		conn_state = state->connector_states[i];
+
+		if (!conn_state)
+			continue;
+
+		WARN_ON(!!conn_state->best_encoder != !!conn_state->crtc);
+
+		if (!conn_state->crtc || !conn_state->best_encoder)
+			continue;
+
+		crtc_state =
+			state->crtc_states[drm_crtc_index(conn_state->crtc)];
+
+		/*
+		 * Each encoder has at most one connector (since we always steal
+		 * it away), so we won't call ->mode_fixup twice.
+		 */
+		encoder = conn_state->best_encoder;
+		funcs = encoder->helper_private;
+
+		if (encoder->bridge && encoder->bridge->funcs->mode_fixup) {
+			ret = encoder->bridge->funcs->mode_fixup(
+					encoder->bridge, &crtc_state->mode,
+					&crtc_state->adjusted_mode);
+			if (!ret) {
+				DRM_DEBUG_KMS("Bridge fixup failed\n");
+				return -EINVAL;
+			}
+		}
+
+
+		ret = funcs->mode_fixup(encoder, &crtc_state->mode,
+					&crtc_state->adjusted_mode);
+		if (!ret) {
+			DRM_DEBUG_KMS("[ENCODER:%d:%s] fixup failed\n",
+				      encoder->base.id, encoder->name);
+			return -EINVAL;
+		}
+	}
+
+	for (i = 0; i < ncrtcs; i++) {
+		struct drm_crtc_helper_funcs *funcs;
+		struct drm_crtc *crtc;
+
+		crtc_state = state->crtc_states[i];
+		crtc = state->crtcs[i];
+
+		if (!crtc_state || !crtc_state->mode_changed)
+			continue;
+
+		funcs = crtc->helper_private;
+		ret = funcs->mode_fixup(crtc, &crtc_state->mode,
+					&crtc_state->adjusted_mode);
+		if (!ret) {
+			DRM_DEBUG_KMS("[CRTC:%d] fixup failed\n",
+				      crtc->base.id);
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
+static int
+drm_atomic_helper_check_prepare(struct drm_device *dev,
+				struct drm_atomic_state *state)
+{
+	int ncrtcs = dev->mode_config.num_crtc;
+	int nconnectors = dev->mode_config.num_connector;
+	struct drm_crtc *crtc;
+	struct drm_crtc_state *crtc_state;
+	int i, ret;
+
+	for (i = 0; i < ncrtcs; i++) {
+		crtc = state->crtcs[i];
+		crtc_state = state->crtc_states[i];
+
+		if (!crtc)
+			continue;
+
+		if (!drm_mode_equal(&crtc->state->mode, &crtc_state->mode)) {
+			DRM_DEBUG_KMS("[CRTC:%d] mode changed\n",
+				      crtc->base.id);
+			crtc_state->mode_changed = true;
+		}
+
+		if (crtc->state->enable != crtc_state->enable) {
+			DRM_DEBUG_KMS("[CRTC:%d] enable changed\n",
+				      crtc->base.id);
+			crtc_state->mode_changed = true;
+		}
+	}
+
+	for (i = 0; i < nconnectors; i++) {
+		/*
+		 * This only sets crtc->mode_changed for routing changes,
+		 * drivers must set crtc->mode_changed themselves when connector
+		 * properties need to be updated.
+		 */
+		ret = update_connector_routing(state, i);
+		if (ret)
+			return ret;
+	}
+
+	/*
+	 * After all the routing has been prepared we need to add in any
+	 * connector which is itself unchanged, but who's crtc changes it's
+	 * configuration. This must be done before calling mode_fixup in case a
+	 * crtc only changed its mode but has the same set of connectors.
+	 */
+	for (i = 0; i < ncrtcs; i++) {
+		int num_connectors;
+
+		crtc = state->crtcs[i];
+		crtc_state = state->crtc_states[i];
+
+		if (!crtc || !crtc_state->mode_changed)
+			continue;
+
+		DRM_DEBUG_KMS("[CRTC:%d] needs full modeset, enable: %c\n",
+			      crtc->base.id,
+			      crtc_state->enable ? 'y' : 'n');
+
+		ret = drm_atomic_add_affected_connectors(state, crtc);
+		if (ret != 0)
+			return ret;
+
+		num_connectors = drm_atomic_connectors_for_crtc(state,
+								crtc);
+
+		if (crtc_state->enable != !!num_connectors) {
+			DRM_DEBUG_KMS("[CRTC:%d] enabled/connectors mismatch\n",
+				      crtc->base.id);
+
+			return -EINVAL;
+		}
+	}
+
+	return mode_fixup(state);
+}
+
 /**
  * drm_atomic_helper_check - validate state object
  * @dev: DRM device
@@ -78,6 +405,10 @@ int drm_atomic_helper_check(struct drm_device *dev,
 	int ncrtcs = dev->mode_config.num_crtc;
 	int i, ret = 0;
 
+	ret = drm_atomic_helper_check_prepare(dev, state);
+	if (ret)
+		return ret;
+
 	for (i = 0; i < nplanes; i++) {
 		struct drm_plane_helper_funcs *funcs;
 		struct drm_plane *plane = state->planes[i];
@@ -125,6 +456,372 @@ int drm_atomic_helper_check(struct drm_device *dev,
 }
 EXPORT_SYMBOL(drm_atomic_helper_check);
 
+static void
+disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state)
+{
+	int ncrtcs = old_state->dev->mode_config.num_crtc;
+	int nconnectors = old_state->dev->mode_config.num_connector;
+	int i;
+
+	for (i = 0; i < nconnectors; i++) {
+		struct drm_connector_state *old_conn_state;
+		struct drm_connector *connector;
+		struct drm_encoder_helper_funcs *funcs;
+		struct drm_encoder *encoder;
+
+		old_conn_state = old_state->connector_states[i];
+		connector = old_state->connectors[i];
+
+		/* Shut down everything that's in the changeset and currently
+		 * still on. So need to check the old, saved state. */
+		if (!old_conn_state || !old_conn_state->crtc)
+			continue;
+
+		encoder = connector->state->best_encoder;
+
+		if (!encoder)
+			continue;
+
+		funcs = encoder->helper_private;
+
+		/*
+		 * Each encoder has at most one connector (since we always steal
+		 * it away), so we won't call call disable hooks twice.
+		 */
+		if (encoder->bridge)
+			encoder->bridge->funcs->disable(encoder->bridge);
+
+		/* Right function depends upon target state. */
+		if (connector->state->crtc)
+			funcs->prepare(encoder);
+		else if (funcs->disable)
+			funcs->disable(encoder);
+		else
+			funcs->dpms(encoder, DRM_MODE_DPMS_OFF);
+
+		if (encoder->bridge)
+			encoder->bridge->funcs->post_disable(encoder->bridge);
+	}
+
+	for (i = 0; i < ncrtcs; i++) {
+		struct drm_crtc_helper_funcs *funcs;
+		struct drm_crtc *crtc;
+
+		crtc = old_state->crtcs[i];
+
+		/* Shut down everything that needs a full modeset. */
+		if (!crtc || !crtc->state->mode_changed)
+			continue;
+
+		funcs = crtc->helper_private;
+
+		/* Right function depends upon target state. */
+		if (crtc->state->enable)
+			funcs->prepare(crtc);
+		else if (funcs->disable)
+			funcs->disable(crtc);
+		else
+			funcs->dpms(crtc, DRM_MODE_DPMS_OFF);
+	}
+}
+
+static void
+set_routing_links(struct drm_device *dev, struct drm_atomic_state *old_state)
+{
+	int nconnectors = dev->mode_config.num_connector;
+	int ncrtcs = old_state->dev->mode_config.num_crtc;
+	int i;
+
+	/* clear out existing links */
+	for (i = 0; i < nconnectors; i++) {
+		struct drm_connector *connector;
+
+		connector = old_state->connectors[i];
+
+		if (!connector || !connector->encoder)
+			continue;
+
+		WARN_ON(!connector->encoder->crtc);
+
+		connector->encoder->crtc = NULL;
+		connector->encoder = NULL;
+	}
+
+	/* set new links */
+	for (i = 0; i < nconnectors; i++) {
+		struct drm_connector *connector;
+
+		connector = old_state->connectors[i];
+
+		if (!connector || !connector->state->crtc)
+			continue;
+
+		if (WARN_ON(!connector->state->best_encoder))
+			continue;
+
+		connector->encoder = connector->state->best_encoder;
+		connector->encoder->crtc = connector->state->crtc;
+	}
+
+	/* set legacy state in the crtc structure */
+	for (i = 0; i < ncrtcs; i++) {
+		struct drm_crtc *crtc;
+
+		crtc = old_state->crtcs[i];
+
+		if (!crtc)
+			continue;
+
+		crtc->mode = crtc->state->mode;
+		crtc->enabled = crtc->state->enable;
+		crtc->x = crtc->primary->state->src_x >> 16;
+		crtc->y = crtc->primary->state->src_y >> 16;
+	}
+}
+
+static void
+crtc_set_mode(struct drm_device *dev, struct drm_atomic_state *old_state)
+{
+	int ncrtcs = old_state->dev->mode_config.num_crtc;
+	int nconnectors = old_state->dev->mode_config.num_connector;
+	int i;
+
+	for (i = 0; i < ncrtcs; i++) {
+		struct drm_crtc_helper_funcs *funcs;
+		struct drm_crtc *crtc;
+
+		crtc = old_state->crtcs[i];
+
+		if (!crtc || !crtc->state->mode_changed)
+			continue;
+
+		funcs = crtc->helper_private;
+
+		if (crtc->state->enable)
+			funcs->mode_set_nofb(crtc);
+	}
+
+	for (i = 0; i < nconnectors; i++) {
+		struct drm_connector *connector;
+		struct drm_crtc_state *new_crtc_state;
+		struct drm_encoder_helper_funcs *funcs;
+		struct drm_encoder *encoder;
+		struct drm_display_mode *mode, *adjusted_mode;
+
+		connector = old_state->connectors[i];
+
+		if (!connector || !connector->state->best_encoder)
+			continue;
+
+		encoder = connector->state->best_encoder;
+		funcs = encoder->helper_private;
+		new_crtc_state = connector->state->crtc->state;
+		mode = &new_crtc_state->mode;
+		adjusted_mode = &new_crtc_state->adjusted_mode;
+
+		/*
+		 * Each encoder has at most one connector (since we always steal
+		 * it away), so we won't call call mode_set hooks twice.
+		 */
+		funcs->mode_set(encoder, mode, adjusted_mode);
+
+		if (encoder->bridge && encoder->bridge->funcs->mode_set)
+			encoder->bridge->funcs->mode_set(encoder->bridge,
+							 mode, adjusted_mode);
+	}
+}
+
+/**
+ * drm_atomic_helper_commit_pre_planes - modeset commit before plane updates
+ * @dev: DRM device
+ * @state: atomic state
+ *
+ * This function commits the modeset changes that need to be committed before
+ * updating planes. It shuts down all the outputs that need to be shut down and
+ * prepares them (if required) with the new mode.
+ */
+void drm_atomic_helper_commit_pre_planes(struct drm_device *dev,
+					 struct drm_atomic_state *state)
+{
+	disable_outputs(dev, state);
+	set_routing_links(dev, state);
+	crtc_set_mode(dev, state);
+}
+EXPORT_SYMBOL(drm_atomic_helper_commit_pre_planes);
+
+/**
+ * drm_atomic_helper_commit_post_planes - modeset commit after plane updates
+ * @dev: DRM device
+ * @old_state: atomic state object with old state structures
+ *
+ * This function commits the modeset changes that need to be committed after
+ * updating planes: It enables all the outputs with the new configuration which
+ * had to be turned off for the update.
+ */
+void drm_atomic_helper_commit_post_planes(struct drm_device *dev,
+					  struct drm_atomic_state *old_state)
+{
+	int ncrtcs = old_state->dev->mode_config.num_crtc;
+	int nconnectors = old_state->dev->mode_config.num_connector;
+	int i;
+
+	for (i = 0; i < ncrtcs; i++) {
+		struct drm_crtc_helper_funcs *funcs;
+		struct drm_crtc *crtc;
+
+		crtc = old_state->crtcs[i];
+
+		/* Need to filter out CRTCs where only planes change. */
+		if (!crtc || !crtc->state->mode_changed)
+			continue;
+
+		funcs = crtc->helper_private;
+
+		if (crtc->state->enable)
+			funcs->commit(crtc);
+	}
+
+	for (i = 0; i < nconnectors; i++) {
+		struct drm_connector *connector;
+		struct drm_encoder_helper_funcs *funcs;
+		struct drm_encoder *encoder;
+
+		connector = old_state->connectors[i];
+
+		if (!connector || !connector->state->best_encoder)
+			continue;
+
+		encoder = connector->state->best_encoder;
+		funcs = encoder->helper_private;
+
+		/*
+		 * Each encoder has at most one connector (since we always steal
+		 * it away), so we won't call call enable hooks twice.
+		 */
+		if (encoder->bridge)
+			encoder->bridge->funcs->pre_enable(encoder->bridge);
+
+		funcs->commit(encoder);
+
+		if (encoder->bridge)
+			encoder->bridge->funcs->enable(encoder->bridge);
+	}
+}
+EXPORT_SYMBOL(drm_atomic_helper_commit_post_planes);
+
+static void
+wait_for_vblanks(struct drm_device *dev, struct drm_atomic_state *old_state)
+{
+	struct drm_crtc *crtc;
+	struct drm_crtc_state *old_crtc_state;
+	int ncrtcs = old_state->dev->mode_config.num_crtc;
+	int i, ret;
+
+	for (i = 0; i < ncrtcs; i++) {
+		crtc = old_state->crtcs[i];
+		old_crtc_state = old_state->crtc_states[i];
+
+		if (!crtc)
+			continue;
+
+		/* No one cares about the old state, so abuse it for tracking
+		 * and store whether we hold a vblank reference (and should do a
+		 * vblank wait) in the ->enable boolean. */
+		old_crtc_state->enable = false;
+
+		if (!crtc->state->enable)
+			continue;
+
+		ret = drm_crtc_vblank_get(crtc);
+		if (ret != 0)
+			continue;
+
+		old_crtc_state->enable = true;
+		old_crtc_state->last_vblank_count = drm_vblank_count(dev, i);
+	}
+
+	for (i = 0; i < ncrtcs; i++) {
+		crtc = old_state->crtcs[i];
+		old_crtc_state = old_state->crtc_states[i];
+
+		if (!crtc || !old_crtc_state->enable)
+			continue;
+
+		ret = wait_event_timeout(dev->vblank[i].queue,
+				old_crtc_state->last_vblank_count !=
+					drm_vblank_count(dev, i),
+				msecs_to_jiffies(50));
+
+		drm_crtc_vblank_put(crtc);
+	}
+}
+
+/**
+ * drm_atomic_helper_commit - commit validated state object
+ * @dev: DRM device
+ * @state: the driver state object
+ * @async: asynchronous commit
+ *
+ * This function commits a with drm_atomic_helper_check() pre-validated state
+ * object. This can still fail when e.g. the framebuffer reservation fails. For
+ * now this doesn't implement asynchronous commits.
+ *
+ * RETURNS
+ * Zero for success or -errno.
+ */
+int drm_atomic_helper_commit(struct drm_device *dev,
+			     struct drm_atomic_state *state,
+			     bool async)
+{
+	int ret;
+
+	if (async)
+		return -EBUSY;
+
+	ret = drm_atomic_helper_prepare_planes(dev, state);
+	if (ret)
+		return ret;
+
+	/*
+	 * This is the point of no return - everything below never fails except
+	 * when the hw goes bonghits. Which means we can commit the new state on
+	 * the software side now.
+	 */
+
+	drm_atomic_helper_swap_state(dev, state);
+
+	/*
+	 * Everything below can be run asynchronously without the need to grab
+	 * any modeset locks at all under one conditions: It must be guaranteed
+	 * that the asynchronous work has either been cancelled (if the driver
+	 * supports it, which at least requires that the framebuffers get
+	 * cleaned up with drm_atomic_helper_cleanup_planes()) or completed
+	 * before the new state gets committed on the software side with
+	 * drm_atomic_helper_swap_state().
+	 *
+	 * This scheme allows new atomic state updates to be prepared and
+	 * checked in parallel to the asynchronous completion of the previous
+	 * update. Which is important since compositors need to figure out the
+	 * composition of the next frame right after having submitted the
+	 * current layout.
+	 */
+
+	drm_atomic_helper_commit_pre_planes(dev, state);
+
+	drm_atomic_helper_commit_planes(dev, state);
+
+	drm_atomic_helper_commit_post_planes(dev, state);
+
+	wait_for_vblanks(dev, state);
+
+	drm_atomic_helper_cleanup_planes(dev, state);
+
+	drm_atomic_state_free(state);
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_atomic_helper_commit);
+
 /**
  * drm_atomic_helper_prepare_planes - prepare plane resources after commit
  * @dev: DRM device
diff --git a/drivers/gpu/drm/drm_crtc_helper.c b/drivers/gpu/drm/drm_crtc_helper.c
index 95ecbb1..46728a8 100644
--- a/drivers/gpu/drm/drm_crtc_helper.c
+++ b/drivers/gpu/drm/drm_crtc_helper.c
@@ -927,6 +927,7 @@ int drm_helper_crtc_mode_set(struct drm_crtc *crtc, struct drm_display_mode *mod
 
 	crtc_state->enable = true;
 	crtc_state->planes_changed = true;
+	crtc_state->mode_changed = true;
 	drm_mode_copy(&crtc_state->mode, mode);
 	drm_mode_copy(&crtc_state->adjusted_mode, adjusted_mode);
 
diff --git a/include/drm/drm_atomic_helper.h b/include/drm/drm_atomic_helper.h
index 79938c6..9781ce7 100644
--- a/include/drm/drm_atomic_helper.h
+++ b/include/drm/drm_atomic_helper.h
@@ -30,6 +30,14 @@
 
 int drm_atomic_helper_check(struct drm_device *dev,
 			    struct drm_atomic_state *state);
+int drm_atomic_helper_commit(struct drm_device *dev,
+			     struct drm_atomic_state *state,
+			     bool async);
+
+void drm_atomic_helper_commit_pre_planes(struct drm_device *dev,
+					 struct drm_atomic_state *state);
+void drm_atomic_helper_commit_post_planes(struct drm_device *dev,
+					  struct drm_atomic_state *old_state);
 
 int drm_atomic_helper_prepare_planes(struct drm_device *dev,
 				     struct drm_atomic_state *state);
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index 53c8638..bc47d11 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -229,6 +229,9 @@ struct drm_atomic_state;
 /**
  * struct drm_crtc_state - mutable CRTC state
  * @enable: whether the CRTC should be enabled, gates all other state
+ * @mode_changed: for use by helpers and drivers when computing state updates
+ * @last_vblank_count: for helpers and drivers to capture the vblank of the
+ * 	update to ensure framebuffer cleanup isn't done too early
  * @planes_changed: for use by helpers and drivers when computing state updates
  * @adjusted_mode: for use by helpers and drivers to compute adjusted mode timings
  * @mode: current mode timings
@@ -241,6 +244,10 @@ struct drm_crtc_state {
 
 	/* computed state bits used by helpers and drivers */
 	bool planes_changed : 1;
+	bool mode_changed : 1;
+
+	/* last_vblank_count: for vblank waits before cleanup */
+	u32 last_vblank_count;
 
 	/* adjusted_mode: for use by helpers and drivers */
 	struct drm_display_mode adjusted_mode;
@@ -426,11 +433,14 @@ struct drm_crtc {
 /**
  * struct drm_connector_state - mutable connector state
  * @crtc: CRTC to connect connector to, NULL if disabled
+ * @best_encoder: can be used by helpers and drivers to select the encoder
  * @state: backpointer to global drm_atomic_state
  */
 struct drm_connector_state {
 	struct drm_crtc *crtc;
 
+	struct drm_encoder *best_encoder;
+
 	struct drm_atomic_state *state;
 };