diff --git a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
index 8459aaee8add..9e72133bb64b 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
@@ -233,7 +233,8 @@ static void rcar_du_crtc_update_planes(struct rcar_du_crtc *rcrtc)
 
 	for (i = 0; i < num_planes; ++i) {
 		struct rcar_du_plane *plane = planes[i];
-		unsigned int index = plane->hwindex;
+		struct drm_plane_state *state = plane->plane.state;
+		unsigned int index = to_rcar_du_plane_state(state)->hwindex;
 
 		prio -= 4;
 		dspr |= (index + 1) << prio;
@@ -259,13 +260,13 @@ static void rcar_du_crtc_update_planes(struct rcar_du_crtc *rcrtc)
 		 * split, or through a module parameter). Flicker would then
 		 * occur only if we need to break the pre-association.
 		 */
-		mutex_lock(&rcrtc->group->planes.lock);
+		mutex_lock(&rcrtc->group->lock);
 		if (rcar_du_group_read(rcrtc->group, DPTSR) != dptsr) {
 			rcar_du_group_write(rcrtc->group, DPTSR, dptsr);
 			if (rcrtc->group->used_crtcs)
 				rcar_du_group_restart(rcrtc->group);
 		}
-		mutex_unlock(&rcrtc->group->planes.lock);
+		mutex_unlock(&rcrtc->group->lock);
 	}
 
 	rcar_du_group_write(rcrtc->group, rcrtc->index % 2 ? DS2PR : DS1PR,
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_group.h b/drivers/gpu/drm/rcar-du/rcar_du_group.h
index 0c38cdcda4ca..ed36433fbe84 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_group.h
+++ b/drivers/gpu/drm/rcar-du/rcar_du_group.h
@@ -14,6 +14,8 @@
 #ifndef __RCAR_DU_GROUP_H__
 #define __RCAR_DU_GROUP_H__
 
+#include <linux/mutex.h>
+
 #include "rcar_du_plane.h"
 
 struct rcar_du_device;
@@ -25,6 +27,7 @@ struct rcar_du_device;
  * @index: group index
  * @use_count: number of users of the group (rcar_du_group_(get|put))
  * @used_crtcs: number of CRTCs currently in use
+ * @lock: protects the DPTSR register
  * @planes: planes handled by the group
  */
 struct rcar_du_group {
@@ -35,6 +38,8 @@ struct rcar_du_group {
 	unsigned int use_count;
 	unsigned int used_crtcs;
 
+	struct mutex lock;
+
 	struct rcar_du_planes planes;
 };
 
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_kms.c b/drivers/gpu/drm/rcar-du/rcar_du_kms.c
index 8bc7242ba979..fb052bca574f 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_kms.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_kms.c
@@ -189,9 +189,206 @@ static void rcar_du_output_poll_changed(struct drm_device *dev)
 }
 
 /* -----------------------------------------------------------------------------
- * Atomic Updates
+ * Atomic Check and Update
  */
 
+/*
+ * Atomic hardware plane allocator
+ *
+ * The hardware plane allocator is solely based on the atomic plane states
+ * without keeping any external state to avoid races between .atomic_check()
+ * and .atomic_commit().
+ *
+ * The core idea is to avoid using a free planes bitmask that would need to be
+ * shared between check and commit handlers with a collective knowledge based on
+ * the allocated hardware plane(s) for each KMS plane. The allocator then loops
+ * over all plane states to compute the free planes bitmask, allocates hardware
+ * planes based on that bitmask, and stores the result back in the plane states.
+ *
+ * For this to work we need to access the current state of planes not touched by
+ * the atomic update. To ensure that it won't be modified, we need to lock all
+ * planes using drm_atomic_get_plane_state(). This effectively serializes atomic
+ * updates from .atomic_check() up to completion (when swapping the states if
+ * the check step has succeeded) or rollback (when freeing the states if the
+ * check step has failed).
+ *
+ * Allocation is performed in the .atomic_check() handler and applied
+ * automatically when the core swaps the old and new states.
+ */
+
+static bool rcar_du_plane_needs_realloc(struct rcar_du_plane *plane,
+					struct rcar_du_plane_state *state)
+{
+	const struct rcar_du_format_info *cur_format;
+
+	cur_format = to_rcar_du_plane_state(plane->plane.state)->format;
+
+	/* Lowering the number of planes doesn't strictly require reallocation
+	 * as the extra hardware plane will be freed when committing, but doing
+	 * so could lead to more fragmentation.
+	 */
+	return !cur_format || cur_format->planes != state->format->planes;
+}
+
+static unsigned int rcar_du_plane_hwmask(struct rcar_du_plane_state *state)
+{
+	unsigned int mask;
+
+	if (state->hwindex == -1)
+		return 0;
+
+	mask = 1 << state->hwindex;
+	if (state->format->planes == 2)
+		mask |= 1 << ((state->hwindex + 1) % 8);
+
+	return mask;
+}
+
+static int rcar_du_plane_hwalloc(unsigned int num_planes, unsigned int free)
+{
+	unsigned int i;
+
+	for (i = 0; i < RCAR_DU_NUM_HW_PLANES; ++i) {
+		if (!(free & (1 << i)))
+			continue;
+
+		if (num_planes == 1 || free & (1 << ((i + 1) % 8)))
+			break;
+	}
+
+	return i == RCAR_DU_NUM_HW_PLANES ? -EBUSY : i;
+}
+
+static int rcar_du_atomic_check(struct drm_device *dev,
+				struct drm_atomic_state *state)
+{
+	struct rcar_du_device *rcdu = dev->dev_private;
+	unsigned int group_freed_planes[RCAR_DU_MAX_GROUPS] = { 0, };
+	unsigned int group_free_planes[RCAR_DU_MAX_GROUPS] = { 0, };
+	bool needs_realloc = false;
+	unsigned int groups = 0;
+	unsigned int i;
+	int ret;
+
+	ret = drm_atomic_helper_check(dev, state);
+	if (ret < 0)
+		return ret;
+
+	/* Check if hardware planes need to be reallocated. */
+	for (i = 0; i < dev->mode_config.num_total_plane; ++i) {
+		struct rcar_du_plane_state *plane_state;
+		struct rcar_du_plane *plane;
+		unsigned int index;
+
+		if (!state->planes[i])
+			continue;
+
+		plane = to_rcar_plane(state->planes[i]);
+		plane_state = to_rcar_du_plane_state(state->plane_states[i]);
+
+		/* If the plane is being disabled we don't need to go through
+		 * the full reallocation procedure. Just mark the hardware
+		 * plane(s) as freed.
+		 */
+		if (!plane_state->format) {
+			index = plane - plane->group->planes.planes;
+			group_freed_planes[plane->group->index] |= 1 << index;
+			plane_state->hwindex = -1;
+			continue;
+		}
+
+		/* If the plane needs to be reallocated mark it as such, and
+		 * mark the hardware plane(s) as free.
+		 */
+		if (rcar_du_plane_needs_realloc(plane, plane_state)) {
+			groups |= 1 << plane->group->index;
+			needs_realloc = true;
+
+			index = plane - plane->group->planes.planes;
+			group_freed_planes[plane->group->index] |= 1 << index;
+			plane_state->hwindex = -1;
+		}
+	}
+
+	if (!needs_realloc)
+		return 0;
+
+	/* Grab all plane states for the groups that need reallocation to ensure
+	 * locking and avoid racy updates. This serializes the update operation,
+	 * but there's not much we can do about it as that's the hardware
+	 * design.
+	 *
+	 * Compute the used planes mask for each group at the same time to avoid
+	 * looping over the planes separately later.
+	 */
+	while (groups) {
+		unsigned int index = ffs(groups) - 1;
+		struct rcar_du_group *group = &rcdu->groups[index];
+		unsigned int used_planes = 0;
+
+		for (i = 0; i < RCAR_DU_NUM_KMS_PLANES; ++i) {
+			struct rcar_du_plane *plane = &group->planes.planes[i];
+			struct rcar_du_plane_state *plane_state;
+			struct drm_plane_state *s;
+
+			s = drm_atomic_get_plane_state(state, &plane->plane);
+			if (IS_ERR(s))
+				return PTR_ERR(s);
+
+			/* If the plane has been freed in the above loop its
+			 * hardware planes must not be added to the used planes
+			 * bitmask. However, the current state doesn't reflect
+			 * the free state yet, as we've modified the new state
+			 * above. Use the local freed planes list to check for
+			 * that condition instead.
+			 */
+			if (group_freed_planes[index] & (1 << i))
+				continue;
+
+			plane_state = to_rcar_du_plane_state(plane->plane.state);
+			used_planes |= rcar_du_plane_hwmask(plane_state);
+		}
+
+		group_free_planes[index] = 0xff & ~used_planes;
+		groups &= ~(1 << index);
+	}
+
+	/* Reallocate hardware planes for each plane that needs it. */
+	for (i = 0; i < dev->mode_config.num_total_plane; ++i) {
+		struct rcar_du_plane_state *plane_state;
+		struct rcar_du_plane *plane;
+		int idx;
+
+		if (!state->planes[i])
+			continue;
+
+		plane = to_rcar_plane(state->planes[i]);
+		plane_state = to_rcar_du_plane_state(state->plane_states[i]);
+
+		/* Skip planes that are being disabled or don't need to be
+		 * reallocated.
+		 */
+		if (!plane_state->format ||
+		    !rcar_du_plane_needs_realloc(plane, plane_state))
+			continue;
+
+		idx = rcar_du_plane_hwalloc(plane_state->format->planes,
+					group_free_planes[plane->group->index]);
+		if (idx < 0) {
+			dev_dbg(rcdu->dev, "%s: no available hardware plane\n",
+				__func__);
+			return idx;
+		}
+
+		plane_state->hwindex = idx;
+
+		group_free_planes[plane->group->index] &=
+			~rcar_du_plane_hwmask(plane_state);
+	}
+
+	return 0;
+}
+
 struct rcar_du_commit {
 	struct work_struct work;
 	struct drm_device *dev;
@@ -292,7 +489,7 @@ static int rcar_du_atomic_commit(struct drm_device *dev,
 static const struct drm_mode_config_funcs rcar_du_mode_config_funcs = {
 	.fb_create = rcar_du_fb_create,
 	.output_poll_changed = rcar_du_output_poll_changed,
-	.atomic_check = drm_atomic_helper_check,
+	.atomic_check = rcar_du_atomic_check,
 	.atomic_commit = rcar_du_atomic_commit,
 };
 
@@ -498,6 +695,8 @@ int rcar_du_modeset_init(struct rcar_du_device *rcdu)
 	for (i = 0; i < num_groups; ++i) {
 		struct rcar_du_group *rgrp = &rcdu->groups[i];
 
+		mutex_init(&rgrp->lock);
+
 		rgrp->dev = rcdu;
 		rgrp->mmio_offset = mmio_offsets[i];
 		rgrp->index = i;
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_plane.c b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
index 58b9e02e6910..35a2f04ab799 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_plane.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
@@ -28,11 +28,6 @@
 #define RCAR_DU_COLORKEY_SOURCE		(1 << 24)
 #define RCAR_DU_COLORKEY_MASK		(1 << 24)
 
-static inline struct rcar_du_plane *to_rcar_plane(struct drm_plane *plane)
-{
-	return container_of(plane, struct rcar_du_plane, plane);
-}
-
 static u32 rcar_du_plane_read(struct rcar_du_group *rgrp,
 			      unsigned int index, u32 reg)
 {
@@ -47,90 +42,6 @@ static void rcar_du_plane_write(struct rcar_du_group *rgrp,
 		      data);
 }
 
-static int rcar_du_plane_reserve_check(struct rcar_du_plane *plane,
-		const struct rcar_du_format_info *cur_format,
-		const struct rcar_du_format_info *new_format)
-{
-	struct rcar_du_group *rgrp = plane->group;
-	unsigned int free;
-	unsigned int i;
-	int ret;
-
-	mutex_lock(&rgrp->planes.lock);
-
-	free = rgrp->planes.free;
-
-	if (plane->hwindex != -1) {
-		free |= 1 << plane->hwindex;
-		if (cur_format->planes == 2)
-			free |= 1 << ((plane->hwindex + 1) % 8);
-	}
-
-	for (i = 0; i < ARRAY_SIZE(rgrp->planes.planes); ++i) {
-		if (!(free & (1 << i)))
-			continue;
-
-		if (new_format->planes == 1 || free & (1 << ((i + 1) % 8)))
-			break;
-	}
-
-	ret = i == ARRAY_SIZE(rgrp->planes.planes) ? -EBUSY : 0;
-
-	mutex_unlock(&rgrp->planes.lock);
-	return ret;
-}
-
-static int rcar_du_plane_reserve(struct rcar_du_plane *plane,
-				 const struct rcar_du_format_info *format)
-{
-	struct rcar_du_group *rgrp = plane->group;
-	unsigned int i;
-	int ret = -EBUSY;
-
-	mutex_lock(&rgrp->planes.lock);
-
-	for (i = 0; i < RCAR_DU_NUM_HW_PLANES; ++i) {
-		if (!(rgrp->planes.free & (1 << i)))
-			continue;
-
-		if (format->planes == 1 ||
-		    rgrp->planes.free & (1 << ((i + 1) % 8)))
-			break;
-	}
-
-	if (i == RCAR_DU_NUM_HW_PLANES)
-		goto done;
-
-	rgrp->planes.free &= ~(1 << i);
-	if (format->planes == 2)
-		rgrp->planes.free &= ~(1 << ((i + 1) % 8));
-
-	plane->hwindex = i;
-
-	ret = 0;
-
-done:
-	mutex_unlock(&rgrp->planes.lock);
-	return ret;
-}
-
-static void rcar_du_plane_release(struct rcar_du_plane *plane,
-				  const struct rcar_du_format_info *format)
-{
-	struct rcar_du_group *rgrp = plane->group;
-
-	if (plane->hwindex == -1)
-		return;
-
-	mutex_lock(&rgrp->planes.lock);
-	rgrp->planes.free |= 1 << plane->hwindex;
-	if (format->planes == 2)
-		rgrp->planes.free |= 1 << ((plane->hwindex + 1) % 8);
-	mutex_unlock(&rgrp->planes.lock);
-
-	plane->hwindex = -1;
-}
-
 static void rcar_du_plane_setup_fb(struct rcar_du_plane *plane)
 {
 	struct rcar_du_plane_state *state =
@@ -139,7 +50,7 @@ static void rcar_du_plane_setup_fb(struct rcar_du_plane *plane)
 	struct rcar_du_group *rgrp = plane->group;
 	unsigned int src_x = state->state.src_x >> 16;
 	unsigned int src_y = state->state.src_y >> 16;
-	unsigned int index = plane->hwindex;
+	unsigned int index = state->hwindex;
 	struct drm_gem_cma_object *gem;
 	bool interlaced;
 	u32 mwr;
@@ -278,7 +189,7 @@ static void __rcar_du_plane_setup(struct rcar_du_plane *plane,
 	rcar_du_plane_setup_mode(plane, index);
 
 	if (state->format->planes == 2) {
-		if (plane->hwindex != index) {
+		if (state->hwindex != index) {
 			if (state->format->fourcc == DRM_FORMAT_NV12 ||
 			    state->format->fourcc == DRM_FORMAT_NV21)
 				ddcr2 |= PnDDCR2_Y420;
@@ -313,9 +224,9 @@ void rcar_du_plane_setup(struct rcar_du_plane *plane)
 	struct rcar_du_plane_state *state =
 		to_rcar_du_plane_state(plane->plane.state);
 
-	__rcar_du_plane_setup(plane, plane->hwindex);
+	__rcar_du_plane_setup(plane, state->hwindex);
 	if (state->format->planes == 2)
-		__rcar_du_plane_setup(plane, (plane->hwindex + 1) % 8);
+		__rcar_du_plane_setup(plane, (state->hwindex + 1) % 8);
 
 	rcar_du_plane_setup_fb(plane);
 }
@@ -326,12 +237,11 @@ static int rcar_du_plane_atomic_check(struct drm_plane *plane,
 	struct rcar_du_plane_state *rstate = to_rcar_du_plane_state(state);
 	struct rcar_du_plane *rplane = to_rcar_plane(plane);
 	struct rcar_du_device *rcdu = rplane->group->dev;
-	const struct rcar_du_format_info *cur_format;
-	const struct rcar_du_format_info *new_format;
-	int ret;
 
-	if (!state->fb || !state->crtc)
+	if (!state->fb || !state->crtc) {
+		rstate->format = NULL;
 		return 0;
+	}
 
 	if (state->src_w >> 16 != state->crtc_w ||
 	    state->src_h >> 16 != state->crtc_h) {
@@ -339,72 +249,23 @@ static int rcar_du_plane_atomic_check(struct drm_plane *plane,
 		return -EINVAL;
 	}
 
-	cur_format = to_rcar_du_plane_state(plane->state)->format;
-	new_format = rcar_du_format_info(state->fb->pixel_format);
-	if (new_format == NULL) {
+	rstate->format = rcar_du_format_info(state->fb->pixel_format);
+	if (rstate->format == NULL) {
 		dev_dbg(rcdu->dev, "%s: unsupported format %08x\n", __func__,
 			state->fb->pixel_format);
 		return -EINVAL;
 	}
 
-	/* If the number of required planes has changed we will need to
-	 * reallocate hardware planes. Ensure free planes are available.
-	 */
-	if (!cur_format || new_format->planes != cur_format->planes) {
-		ret = rcar_du_plane_reserve_check(rplane, cur_format,
-						  new_format);
-		if (ret < 0) {
-			dev_dbg(rcdu->dev, "%s: no available hardware plane\n",
-				__func__);
-			return ret;
-		}
-	}
-
-	rstate->format = new_format;
-
 	return 0;
 }
 
-static void rcar_du_plane_disable(struct rcar_du_plane *rplane,
-				  const struct rcar_du_format_info *cur_format)
-{
-	struct rcar_du_plane_state *rstate =
-		to_rcar_du_plane_state(rplane->plane.state);
-
-	if (!rplane->plane.state->crtc)
-		return;
-
-	rcar_du_plane_release(rplane, cur_format);
-
-	rstate->format = NULL;
-}
-
 static void rcar_du_plane_atomic_update(struct drm_plane *plane,
 					struct drm_plane_state *old_state)
 {
 	struct rcar_du_plane *rplane = to_rcar_plane(plane);
-	struct drm_plane_state *state = plane->state;
-	struct rcar_du_plane_state *rstate = to_rcar_du_plane_state(state);
-	const struct rcar_du_format_info *cur_format;
-	const struct rcar_du_format_info *new_format;
 
-	cur_format = to_rcar_du_plane_state(old_state)->format;
-	new_format = rstate->format;
-
-	if (!state->crtc) {
-		rcar_du_plane_disable(rplane, cur_format);
-		return;
-	}
-
-	/* Reallocate hardware planes if the number of required planes has
-	 * changed.
-	 */
-	if (!cur_format || new_format->planes != cur_format->planes) {
-		rcar_du_plane_release(rplane, cur_format);
-		rcar_du_plane_reserve(rplane, new_format);
-	}
-
-	rcar_du_plane_setup(rplane);
+	if (plane->state->crtc)
+		rcar_du_plane_setup(rplane);
 }
 
 static const struct drm_plane_helper_funcs rcar_du_plane_helper_funcs = {
@@ -426,6 +287,7 @@ static void rcar_du_plane_reset(struct drm_plane *plane)
 	if (state == NULL)
 		return;
 
+	state->hwindex = -1;
 	state->alpha = 255;
 	state->colorkey = RCAR_DU_COLORKEY_NONE;
 	state->zpos = plane->type == DRM_PLANE_TYPE_PRIMARY ? 0 : 1;
@@ -534,9 +396,6 @@ int rcar_du_planes_init(struct rcar_du_group *rgrp)
 	unsigned int i;
 	int ret;
 
-	mutex_init(&planes->lock);
-	planes->free = 0xff;
-
 	planes->alpha =
 		drm_property_create_range(rcdu->ddev, 0, "alpha", 0, 255);
 	if (planes->alpha == NULL)
@@ -572,7 +431,6 @@ int rcar_du_planes_init(struct rcar_du_group *rgrp)
 		struct rcar_du_plane *plane = &planes->planes[i];
 
 		plane->group = rgrp;
-		plane->hwindex = -1;
 
 		ret = drm_universal_plane_init(rcdu->ddev, &plane->plane, crtcs,
 					       &rcar_du_plane_funcs, formats,
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_plane.h b/drivers/gpu/drm/rcar-du/rcar_du_plane.h
index 0941c4830edd..abff0ebeb195 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_plane.h
+++ b/drivers/gpu/drm/rcar-du/rcar_du_plane.h
@@ -14,8 +14,6 @@
 #ifndef __RCAR_DU_PLANE_H__
 #define __RCAR_DU_PLANE_H__
 
-#include <linux/mutex.h>
-
 #include <drm/drmP.h>
 #include <drm/drm_crtc.h>
 
@@ -33,13 +31,15 @@ struct rcar_du_group;
 struct rcar_du_plane {
 	struct drm_plane plane;
 	struct rcar_du_group *group;
-	int hwindex;		/* 0-based, -1 means unused */
 };
 
+static inline struct rcar_du_plane *to_rcar_plane(struct drm_plane *plane)
+{
+	return container_of(plane, struct rcar_du_plane, plane);
+}
+
 struct rcar_du_planes {
 	struct rcar_du_plane planes[RCAR_DU_NUM_KMS_PLANES];
-	unsigned int free;
-	struct mutex lock;
 
 	struct drm_property *alpha;
 	struct drm_property *colorkey;
@@ -50,6 +50,7 @@ struct rcar_du_plane_state {
 	struct drm_plane_state state;
 
 	const struct rcar_du_format_info *format;
+	int hwindex;		/* 0-based, -1 means unused */
 
 	unsigned int alpha;
 	unsigned int colorkey;