drm/i915: DocBook integration for frontbuffer tracking

I shouldn't ask everyone to do this and fail myself ...

This extracts all the frontbuffer tracking functions into
intel_frontbuffer.c, adds a DOC overview section and also adds the
missing kerneldoc for i915_gem_track_fb and also pulls it into the
same section for convenience.

v2: Don't forget about the header files.

v3: Oops, might check compilation next time around. To make my life
easier drop the increase_pllclock from set_base_atomic since really,
it doesn't matter if you see your Oops or kgdb with a tiny bit of lag.

v4: Try to better explain how to actually use this, requested by Paulo
on irc.

v5: Explain invalidate/flush a bit clearer.

v6: s/business/busyness/
Acked-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Vandana Kannan <vandana.kannan@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

Documentation/DocBook/drm.tmpl

@@ -3803,6 +3803,13 @@ int num_ioctls;</synopsis>
           configuration change.
         </para>
       </sect2>
+      <sect2>
+        <title>Frontbuffer Tracking</title>
+!Pdrivers/gpu/drm/i915/intel_frontbuffer.c frontbuffer tracking
+!Idrivers/gpu/drm/i915/intel_frontbuffer.c
+!Fdrivers/gpu/drm/i915/intel_drv.h intel_frontbuffer_flip
+!Fdrivers/gpu/drm/i915/i915_gem.c i915_gem_track_fb
+      </sect2>
       <sect2>
         <title>Plane Configuration</title>
         <para>

drivers/gpu/drm/i915/Makefile

@@ -43,6 +43,7 @@ i915-y += intel_renderstate_gen6.o \
 # modesetting core code
 i915-y += intel_bios.o \
 	  intel_display.o \
+	  intel_frontbuffer.o \
 	  intel_modes.o \
 	  intel_overlay.o \
 	  intel_sideband.o \

drivers/gpu/drm/i915/i915_gem.c

@@ -5077,6 +5077,15 @@ int i915_gem_open(struct drm_device *dev, struct drm_file *file)
 	return ret;
 }
 
+/**
+ * i915_gem_track_fb - update frontbuffer tracking
+ * old: current GEM buffer for the frontbuffer slots
+ * new: new GEM buffer for the frontbuffer slots
+ * frontbuffer_bits: bitmask of frontbuffer slots
+ *
+ * This updates the frontbuffer tracking bits @frontbuffer_bits by clearing them
+ * from @old and setting them in @new. Both @old and @new can be NULL.
+ */
 void i915_gem_track_fb(struct drm_i915_gem_object *old,
 		       struct drm_i915_gem_object *new,
 		       unsigned frontbuffer_bits)

drivers/gpu/drm/i915/intel_display.c

@@ -76,8 +76,6 @@ static const uint32_t intel_cursor_formats[] = {
 #define DIV_ROUND_CLOSEST_ULL(ll, d)	\
 ({ unsigned long long _tmp = (ll)+(d)/2; do_div(_tmp, d); _tmp; })
 
-static void intel_increase_pllclock(struct drm_device *dev,
-				    enum pipe pipe);
 static void intel_crtc_update_cursor(struct drm_crtc *crtc, bool on);
 
 static void i9xx_crtc_clock_get(struct intel_crtc *crtc,
@@ -1138,8 +1136,8 @@ void assert_fdi_rx_pll(struct drm_i915_private *dev_priv,
 	     state_string(state), state_string(cur_state));
 }
 
-static void assert_panel_unlocked(struct drm_i915_private *dev_priv,
-				  enum pipe pipe)
+void assert_panel_unlocked(struct drm_i915_private *dev_priv,
+			   enum pipe pipe)
 {
 	struct drm_device *dev = dev_priv->dev;
 	int pp_reg;
@@ -2631,7 +2629,6 @@ intel_pipe_set_base_atomic(struct drm_crtc *crtc, struct drm_framebuffer *fb,
 
 	if (dev_priv->display.disable_fbc)
 		dev_priv->display.disable_fbc(dev);
-	intel_increase_pllclock(dev, to_intel_crtc(crtc)->pipe);
 
 	dev_priv->display.update_primary_plane(crtc, fb, x, y);
 
@@ -8986,35 +8983,6 @@ struct drm_display_mode *intel_crtc_mode_get(struct drm_device *dev,
 	return mode;
 }
 
-static void intel_increase_pllclock(struct drm_device *dev,
-				    enum pipe pipe)
-{
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	int dpll_reg = DPLL(pipe);
-	int dpll;
-
-	if (!HAS_GMCH_DISPLAY(dev))
-		return;
-
-	if (!dev_priv->lvds_downclock_avail)
-		return;
-
-	dpll = I915_READ(dpll_reg);
-	if (!HAS_PIPE_CXSR(dev) && (dpll & DISPLAY_RATE_SELECT_FPA1)) {
-		DRM_DEBUG_DRIVER("upclocking LVDS\n");
-
-		assert_panel_unlocked(dev_priv, pipe);
-
-		dpll &= ~DISPLAY_RATE_SELECT_FPA1;
-		I915_WRITE(dpll_reg, dpll);
-		intel_wait_for_vblank(dev, pipe);
-
-		dpll = I915_READ(dpll_reg);
-		if (dpll & DISPLAY_RATE_SELECT_FPA1)
-			DRM_DEBUG_DRIVER("failed to upclock LVDS!\n");
-	}
-}
-
 static void intel_decrease_pllclock(struct drm_crtc *crtc)
 {
 	struct drm_device *dev = crtc->dev;
@@ -9090,188 +9058,6 @@ void intel_mark_idle(struct drm_device *dev)
 	intel_runtime_pm_put(dev_priv);
 }
 
-
-/**
- * intel_mark_fb_busy - mark given planes as busy
- * @dev: DRM device
- * @frontbuffer_bits: bits for the affected planes
- * @ring: optional ring for asynchronous commands
- *
- * This function gets called every time the screen contents change. It can be
- * used to keep e.g. the update rate at the nominal refresh rate with DRRS.
- */
-static void intel_mark_fb_busy(struct drm_device *dev,
-			       unsigned frontbuffer_bits,
-			       struct intel_engine_cs *ring)
-{
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	enum pipe pipe;
-
-	if (!i915.powersave)
-		return;
-
-	for_each_pipe(dev_priv, pipe) {
-		if (!(frontbuffer_bits & INTEL_FRONTBUFFER_ALL_MASK(pipe)))
-			continue;
-
-		intel_increase_pllclock(dev, pipe);
-		if (ring && intel_fbc_enabled(dev))
-			ring->fbc_dirty = true;
-	}
-}
-
-/**
- * intel_fb_obj_invalidate - invalidate frontbuffer object
- * @obj: GEM object to invalidate
- * @ring: set for asynchronous rendering
- *
- * This function gets called every time rendering on the given object starts and
- * frontbuffer caching (fbc, low refresh rate for DRRS, panel self refresh) must
- * be invalidated. If @ring is non-NULL any subsequent invalidation will be delayed
- * until the rendering completes or a flip on this frontbuffer plane is
- * scheduled.
- */
-void intel_fb_obj_invalidate(struct drm_i915_gem_object *obj,
-			     struct intel_engine_cs *ring)
-{
-	struct drm_device *dev = obj->base.dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-
-	WARN_ON(!mutex_is_locked(&dev->struct_mutex));
-
-	if (!obj->frontbuffer_bits)
-		return;
-
-	if (ring) {
-		mutex_lock(&dev_priv->fb_tracking.lock);
-		dev_priv->fb_tracking.busy_bits
-			|= obj->frontbuffer_bits;
-		dev_priv->fb_tracking.flip_bits
-			&= ~obj->frontbuffer_bits;
-		mutex_unlock(&dev_priv->fb_tracking.lock);
-	}
-
-	intel_mark_fb_busy(dev, obj->frontbuffer_bits, ring);
-
-	intel_edp_psr_invalidate(dev, obj->frontbuffer_bits);
-}
-
-/**
- * intel_frontbuffer_flush - flush frontbuffer
- * @dev: DRM device
- * @frontbuffer_bits: frontbuffer plane tracking bits
- *
- * This function gets called every time rendering on the given planes has
- * completed and frontbuffer caching can be started again. Flushes will get
- * delayed if they're blocked by some oustanding asynchronous rendering.
- *
- * Can be called without any locks held.
- */
-void intel_frontbuffer_flush(struct drm_device *dev,
-			     unsigned frontbuffer_bits)
-{
-	struct drm_i915_private *dev_priv = dev->dev_private;
-
-	/* Delay flushing when rings are still busy.*/
-	mutex_lock(&dev_priv->fb_tracking.lock);
-	frontbuffer_bits &= ~dev_priv->fb_tracking.busy_bits;
-	mutex_unlock(&dev_priv->fb_tracking.lock);
-
-	intel_mark_fb_busy(dev, frontbuffer_bits, NULL);
-
-	intel_edp_psr_flush(dev, frontbuffer_bits);
-
-	/*
-	 * FIXME: Unconditional fbc flushing here is a rather gross hack and
-	 * needs to be reworked into a proper frontbuffer tracking scheme like
-	 * psr employs.
-	 */
-	if (IS_BROADWELL(dev))
-		gen8_fbc_sw_flush(dev, FBC_REND_CACHE_CLEAN);
-}
-
-/**
- * intel_fb_obj_flush - flush frontbuffer object
- * @obj: GEM object to flush
- * @retire: set when retiring asynchronous rendering
- *
- * This function gets called every time rendering on the given object has
- * completed and frontbuffer caching can be started again. If @retire is true
- * then any delayed flushes will be unblocked.
- */
-void intel_fb_obj_flush(struct drm_i915_gem_object *obj,
-			bool retire)
-{
-	struct drm_device *dev = obj->base.dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	unsigned frontbuffer_bits;
-
-	WARN_ON(!mutex_is_locked(&dev->struct_mutex));
-
-	if (!obj->frontbuffer_bits)
-		return;
-
-	frontbuffer_bits = obj->frontbuffer_bits;
-
-	if (retire) {
-		mutex_lock(&dev_priv->fb_tracking.lock);
-		/* Filter out new bits since rendering started. */
-		frontbuffer_bits &= dev_priv->fb_tracking.busy_bits;
-
-		dev_priv->fb_tracking.busy_bits &= ~frontbuffer_bits;
-		mutex_unlock(&dev_priv->fb_tracking.lock);
-	}
-
-	intel_frontbuffer_flush(dev, frontbuffer_bits);
-}
-
-/**
- * intel_frontbuffer_flip_prepare - prepare asnychronous frontbuffer flip
- * @dev: DRM device
- * @frontbuffer_bits: frontbuffer plane tracking bits
- *
- * This function gets called after scheduling a flip on @obj. The actual
- * frontbuffer flushing will be delayed until completion is signalled with
- * intel_frontbuffer_flip_complete. If an invalidate happens in between this
- * flush will be cancelled.
- *
- * Can be called without any locks held.
- */
-void intel_frontbuffer_flip_prepare(struct drm_device *dev,
-				    unsigned frontbuffer_bits)
-{
-	struct drm_i915_private *dev_priv = dev->dev_private;
-
-	mutex_lock(&dev_priv->fb_tracking.lock);
-	dev_priv->fb_tracking.flip_bits
-		|= frontbuffer_bits;
-	mutex_unlock(&dev_priv->fb_tracking.lock);
-}
-
-/**
- * intel_frontbuffer_flip_complete - complete asynchronous frontbuffer flush
- * @dev: DRM device
- * @frontbuffer_bits: frontbuffer plane tracking bits
- *
- * This function gets called after the flip has been latched and will complete
- * on the next vblank. It will execute the fush if it hasn't been cancalled yet.
- *
- * Can be called without any locks held.
- */
-void intel_frontbuffer_flip_complete(struct drm_device *dev,
-				     unsigned frontbuffer_bits)
-{
-	struct drm_i915_private *dev_priv = dev->dev_private;
-
-	mutex_lock(&dev_priv->fb_tracking.lock);
-	/* Mask any cancelled flips. */
-	frontbuffer_bits &= dev_priv->fb_tracking.flip_bits;
-	dev_priv->fb_tracking.flip_bits &= ~frontbuffer_bits;
-	mutex_unlock(&dev_priv->fb_tracking.lock);
-
-	intel_frontbuffer_flush(dev, frontbuffer_bits);
-}
-
 static void intel_crtc_destroy(struct drm_crtc *crtc)
 {
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);

drivers/gpu/drm/i915/intel_drv.h

@@ -801,11 +801,7 @@ void intel_ddi_clock_get(struct intel_encoder *encoder,
 			 struct intel_crtc_config *pipe_config);
 void intel_ddi_set_vc_payload_alloc(struct drm_crtc *crtc, bool state);
 
-/* intel_display.c */
-const char *intel_output_name(int output);
-bool intel_has_pending_fb_unpin(struct drm_device *dev);
-int intel_pch_rawclk(struct drm_device *dev);
-void intel_mark_busy(struct drm_device *dev);
+/* intel_frontbuffer.c */
 void intel_fb_obj_invalidate(struct drm_i915_gem_object *obj,
 			     struct intel_engine_cs *ring);
 void intel_frontbuffer_flip_prepare(struct drm_device *dev,
@@ -833,6 +829,13 @@ void intel_frontbuffer_flip(struct drm_device *dev,
 }
 
 void intel_fb_obj_flush(struct drm_i915_gem_object *obj, bool retire);
+
+
+/* intel_display.c */
+const char *intel_output_name(int output);
+bool intel_has_pending_fb_unpin(struct drm_device *dev);
+int intel_pch_rawclk(struct drm_device *dev);
+void intel_mark_busy(struct drm_device *dev);
 void intel_mark_idle(struct drm_device *dev);
 void intel_crtc_restore_mode(struct drm_crtc *crtc);
 void intel_crtc_control(struct drm_crtc *crtc, bool enable);
@@ -891,6 +894,8 @@ struct intel_shared_dpll *intel_get_shared_dpll(struct intel_crtc *crtc);
 void intel_put_shared_dpll(struct intel_crtc *crtc);
 
 /* modesetting asserts */
+void assert_panel_unlocked(struct drm_i915_private *dev_priv,
+			   enum pipe pipe);
 void assert_pll(struct drm_i915_private *dev_priv,
 		enum pipe pipe, bool state);
 #define assert_pll_enabled(d, p) assert_pll(d, p, true)

drivers/gpu/drm/i915/intel_frontbuffer.c

+/*
+ * Copyright © 2014 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ *
+ * Authors:
+ *	Daniel Vetter <daniel.vetter@ffwll.ch>
+ */
+
+/**
+ * DOC: frontbuffer tracking
+ *
+ * Many features require us to track changes to the currently active
+ * frontbuffer, especially rendering targetted at the frontbuffer.
+ *
+ * To be able to do so GEM tracks frontbuffers using a bitmask for all possible
+ * frontbuffer slots through i915_gem_track_fb(). The function in this file are
+ * then called when the contents of the frontbuffer are invalidated, when
+ * frontbuffer rendering has stopped again to flush out all the changes and when
+ * the frontbuffer is exchanged with a flip. Subsystems interested in
+ * frontbuffer changes (e.g. PSR, FBC, DRRS) should directly put their callbacks
+ * into the relevant places and filter for the frontbuffer slots that they are
+ * interested int.
+ *
+ * On a high level there are two types of powersaving features. The first one
+ * work like a special cache (FBC and PSR) and are interested when they should
+ * stop caching and when to restart caching. This is done by placing callbacks
+ * into the invalidate and the flush functions: At invalidate the caching must
+ * be stopped and at flush time it can be restarted. And maybe they need to know
+ * when the frontbuffer changes (e.g. when the hw doesn't initiate an invalidate
+ * and flush on its own) which can be achieved with placing callbacks into the
+ * flip functions.
+ *
+ * The other type of display power saving feature only cares about busyness
+ * (e.g. DRRS). In that case all three (invalidate, flush and flip) indicate
+ * busyness. There is no direct way to detect idleness. Instead an idle timer
+ * work delayed work should be started from the flush and flip functions and
+ * cancelled as soon as busyness is detected.
+ *
+ * Note that there's also an older frontbuffer activity tracking scheme which
+ * just trackings general activity. This is done by the various mark_busy and
+ * mark_idle functions. For display power management features using these
+ * functions is deprecated and should be avoided.
+ */
+
+#include <drm/drmP.h>
+
+#include "intel_drv.h"
+#include "i915_drv.h"
+
+static void intel_increase_pllclock(struct drm_device *dev,
+				    enum pipe pipe)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	int dpll_reg = DPLL(pipe);
+	int dpll;
+
+	if (!HAS_GMCH_DISPLAY(dev))
+		return;
+
+	if (!dev_priv->lvds_downclock_avail)
+		return;
+
+	dpll = I915_READ(dpll_reg);
+	if (!HAS_PIPE_CXSR(dev) && (dpll & DISPLAY_RATE_SELECT_FPA1)) {
+		DRM_DEBUG_DRIVER("upclocking LVDS\n");
+
+		assert_panel_unlocked(dev_priv, pipe);
+
+		dpll &= ~DISPLAY_RATE_SELECT_FPA1;
+		I915_WRITE(dpll_reg, dpll);
+		intel_wait_for_vblank(dev, pipe);
+
+		dpll = I915_READ(dpll_reg);
+		if (dpll & DISPLAY_RATE_SELECT_FPA1)
+			DRM_DEBUG_DRIVER("failed to upclock LVDS!\n");
+	}
+}
+
+/**
+ * intel_mark_fb_busy - mark given planes as busy
+ * @dev: DRM device
+ * @frontbuffer_bits: bits for the affected planes
+ * @ring: optional ring for asynchronous commands
+ *
+ * This function gets called every time the screen contents change. It can be
+ * used to keep e.g. the update rate at the nominal refresh rate with DRRS.
+ */
+static void intel_mark_fb_busy(struct drm_device *dev,
+			       unsigned frontbuffer_bits,
+			       struct intel_engine_cs *ring)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	enum pipe pipe;
+
+	if (!i915.powersave)
+		return;
+
+	for_each_pipe(dev_priv, pipe) {
+		if (!(frontbuffer_bits & INTEL_FRONTBUFFER_ALL_MASK(pipe)))
+			continue;
+
+		intel_increase_pllclock(dev, pipe);
+		if (ring && intel_fbc_enabled(dev))
+			ring->fbc_dirty = true;
+	}
+}
+
+/**
+ * intel_fb_obj_invalidate - invalidate frontbuffer object
+ * @obj: GEM object to invalidate
+ * @ring: set for asynchronous rendering
+ *
+ * This function gets called every time rendering on the given object starts and
+ * frontbuffer caching (fbc, low refresh rate for DRRS, panel self refresh) must
+ * be invalidated. If @ring is non-NULL any subsequent invalidation will be delayed
+ * until the rendering completes or a flip on this frontbuffer plane is
+ * scheduled.
+ */
+void intel_fb_obj_invalidate(struct drm_i915_gem_object *obj,
+			     struct intel_engine_cs *ring)
+{
+	struct drm_device *dev = obj->base.dev;
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	WARN_ON(!mutex_is_locked(&dev->struct_mutex));
+
+	if (!obj->frontbuffer_bits)
+		return;
+
+	if (ring) {
+		mutex_lock(&dev_priv->fb_tracking.lock);
+		dev_priv->fb_tracking.busy_bits
+			|= obj->frontbuffer_bits;
+		dev_priv->fb_tracking.flip_bits
+			&= ~obj->frontbuffer_bits;
+		mutex_unlock(&dev_priv->fb_tracking.lock);
+	}
+
+	intel_mark_fb_busy(dev, obj->frontbuffer_bits, ring);
+
+	intel_edp_psr_invalidate(dev, obj->frontbuffer_bits);
+}
+
+/**
+ * intel_frontbuffer_flush - flush frontbuffer
+ * @dev: DRM device
+ * @frontbuffer_bits: frontbuffer plane tracking bits
+ *
+ * This function gets called every time rendering on the given planes has
+ * completed and frontbuffer caching can be started again. Flushes will get
+ * delayed if they're blocked by some oustanding asynchronous rendering.
+ *
+ * Can be called without any locks held.
+ */
+void intel_frontbuffer_flush(struct drm_device *dev,
+			     unsigned frontbuffer_bits)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	/* Delay flushing when rings are still busy.*/
+	mutex_lock(&dev_priv->fb_tracking.lock);
+	frontbuffer_bits &= ~dev_priv->fb_tracking.busy_bits;
+	mutex_unlock(&dev_priv->fb_tracking.lock);
+
+	intel_mark_fb_busy(dev, frontbuffer_bits, NULL);
+
+	intel_edp_psr_flush(dev, frontbuffer_bits);
+
+	/*
+	 * FIXME: Unconditional fbc flushing here is a rather gross hack and
+	 * needs to be reworked into a proper frontbuffer tracking scheme like
+	 * psr employs.
+	 */
+	if (IS_BROADWELL(dev))
+		gen8_fbc_sw_flush(dev, FBC_REND_CACHE_CLEAN);
+}
+
+/**
+ * intel_fb_obj_flush - flush frontbuffer object
+ * @obj: GEM object to flush
+ * @retire: set when retiring asynchronous rendering
+ *
+ * This function gets called every time rendering on the given object has
+ * completed and frontbuffer caching can be started again. If @retire is true
+ * then any delayed flushes will be unblocked.
+ */
+void intel_fb_obj_flush(struct drm_i915_gem_object *obj,
+			bool retire)
+{
+	struct drm_device *dev = obj->base.dev;
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	unsigned frontbuffer_bits;
+
+	WARN_ON(!mutex_is_locked(&dev->struct_mutex));
+
+	if (!obj->frontbuffer_bits)
+		return;
+
+	frontbuffer_bits = obj->frontbuffer_bits;
+
+	if (retire) {
+		mutex_lock(&dev_priv->fb_tracking.lock);
+		/* Filter out new bits since rendering started. */
+		frontbuffer_bits &= dev_priv->fb_tracking.busy_bits;
+
+		dev_priv->fb_tracking.busy_bits &= ~frontbuffer_bits;
+		mutex_unlock(&dev_priv->fb_tracking.lock);
+	}
+
+	intel_frontbuffer_flush(dev, frontbuffer_bits);
+}
+
+/**
+ * intel_frontbuffer_flip_prepare - prepare asnychronous frontbuffer flip
+ * @dev: DRM device
+ * @frontbuffer_bits: frontbuffer plane tracking bits
+ *
+ * This function gets called after scheduling a flip on @obj. The actual
+ * frontbuffer flushing will be delayed until completion is signalled with
+ * intel_frontbuffer_flip_complete. If an invalidate happens in between this
+ * flush will be cancelled.
+ *
+ * Can be called without any locks held.
+ */
+void intel_frontbuffer_flip_prepare(struct drm_device *dev,
+				    unsigned frontbuffer_bits)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	mutex_lock(&dev_priv->fb_tracking.lock);
+	dev_priv->fb_tracking.flip_bits
+		|= frontbuffer_bits;
+	mutex_unlock(&dev_priv->fb_tracking.lock);
+}
+
+/**
+ * intel_frontbuffer_flip_complete - complete asynchronous frontbuffer flush
+ * @dev: DRM device
+ * @frontbuffer_bits: frontbuffer plane tracking bits
+ *
+ * This function gets called after the flip has been latched and will complete
+ * on the next vblank. It will execute the fush if it hasn't been cancalled yet.
+ *
+ * Can be called without any locks held.
+ */
+void intel_frontbuffer_flip_complete(struct drm_device *dev,
+				     unsigned frontbuffer_bits)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	mutex_lock(&dev_priv->fb_tracking.lock);
+	/* Mask any cancelled flips. */
+	frontbuffer_bits &= dev_priv->fb_tracking.flip_bits;
+	dev_priv->fb_tracking.flip_bits &= ~frontbuffer_bits;
+	mutex_unlock(&dev_priv->fb_tracking.lock);
+
+	intel_frontbuffer_flush(dev, frontbuffer_bits);
+}
+