Nouveau - Nov 2018 - [PATCH v3 0/5] drm/dp_mst: Add some atomic state iterator macros

This patchset does some cleaning up of the atomic VCPI helpers for MST,
and converts nouveau over to using them. I would have included amdgpu in
this patch as well, but at the moment moving them over to the atomic
helpers is nontrivial.

Cc: Daniel Vetter <daniel at ffwll.ch>

Lyude Paul (5):
  drm/dp_mst: Add some atomic state iterator macros
  drm/dp_mst: Start tracking per-port VCPI allocations
  drm/dp_mst: Check payload count in drm_dp_mst_atomic_check()
  drm/nouveau: Use atomic VCPI helpers for MST
  drm/dp_mst: Stop unsetting mstc->port, check connector registration

 drivers/gpu/drm/drm_dp_mst_topology.c   | 229 ++++++++++++++++++++----
 drivers/gpu/drm/i915/intel_display.c    |   4 +
 drivers/gpu/drm/i915/intel_dp_mst.c     |  31 ++--
 drivers/gpu/drm/nouveau/dispnv50/disp.c |  65 +++++--
 include/drm/drm_dp_mst_helper.h         | 100 ++++++++++-
 5 files changed, 359 insertions(+), 70 deletions(-)

-- 
2.19.1

Signed-off-by: Lyude Paul <lyude at redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 include/drm/drm_dp_mst_helper.h | 77 +++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)

diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
index 59f005b419cf..3faceb66f5cb 100644
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -628,4 +628,81 @@ int drm_dp_atomic_release_vcpi_slots(struct
drm_atomic_state *state,
 int drm_dp_send_power_updown_phy(struct drm_dp_mst_topology_mgr *mgr,
 				 struct drm_dp_mst_port *port, bool power_up);
 
+extern const struct drm_private_state_funcs drm_dp_mst_topology_state_funcs;
+
+static inline bool
+__drm_dp_mst_state_iter_get(struct drm_atomic_state *state,
+			    struct drm_dp_mst_topology_mgr **mgr,
+			    struct drm_dp_mst_topology_state **old_state,
+			    struct drm_dp_mst_topology_state **new_state,
+			    int i)
+{
+	struct __drm_private_objs_state *objs_state = &state->private_objs[i];
+
+	if (objs_state->ptr->funcs != &drm_dp_mst_topology_state_funcs)
+		return false;
+
+	*mgr = to_dp_mst_topology_mgr(objs_state->ptr);
+	if (old_state)
+		*old_state = to_dp_mst_topology_state(objs_state->old_state);
+	if (new_state)
+		*new_state = to_dp_mst_topology_state(objs_state->new_state);
+
+	return true;
+}
+
+/**
+ * for_each_oldnew_mst_mgr_in_state - iterate over all DP MST topology
+ * managers in an atomic update
+ * @__state: &struct drm_atomic_state pointer
+ * @mgr: &struct drm_dp_mst_topology_mgr iteration cursor
+ * @old_state: &struct drm_dp_mst_topology_state iteration cursor for the
old
+ * state
+ * @new_state: &struct drm_dp_mst_topology_state iteration cursor for the
new
+ * state
+ * @__i: int iteration cursor, for macro-internal use
+ *
+ * This iterates over all DRM DP MST topology managers in an atomic update,
+ * tracking both old and new state. This is useful in places where the state
+ * delta needs to be considered, for example in atomic check functions.
+ */
+#define for_each_oldnew_mst_mgr_in_state(__state, mgr, old_state, new_state,
__i) \
+	for ((__i) = 0; (__i) < (__state)->num_private_objs; (__i)++) \
+		for_each_if(__drm_dp_mst_state_iter_get((__state), &(mgr),
&(old_state), &(new_state), (__i)))
+
+/**
+ * for_each_old_mst_mgr_in_state - iterate over all DP MST topology managers
+ * in an atomic update
+ * @__state: &struct drm_atomic_state pointer
+ * @mgr: &struct drm_dp_mst_topology_mgr iteration cursor
+ * @old_state: &struct drm_dp_mst_topology_state iteration cursor for the
old
+ * state
+ * @__i: int iteration cursor, for macro-internal use
+ *
+ * This iterates over all DRM DP MST topology managers in an atomic update,
+ * tracking only the old state. This is useful in disable functions, where we
+ * need the old state the hardware is still in.
+ */
+#define for_each_old_mst_mgr_in_state(__state, mgr, old_state, __i) \
+	for ((__i) = 0; (__i) < (__state)->num_private_objs; (__i)++) \
+		for_each_if(__drm_dp_mst_state_iter_get((__state), &(mgr),
&(old_state), NULL, (__i)))
+
+/**
+ * for_each_new_mst_mgr_in_state - iterate over all DP MST topology managers
+ * in an atomic update
+ * @__state: &struct drm_atomic_state pointer
+ * @mgr: &struct drm_dp_mst_topology_mgr iteration cursor
+ * @new_state: &struct drm_dp_mst_topology_state iteration cursor for the
new
+ * state
+ * @__i: int iteration cursor, for macro-internal use
+ *
+ * This iterates over all DRM DP MST topology managers in an atomic update,
+ * tracking only the new state. This is useful in enable functions, where we
+ * need the new state the hardware should be in when the atomic commit
+ * operation has completed.
+ */
+#define for_each_new_mst_mgr_in_state(__state, mgr, new_state, __i) \
+	for ((__i) = 0; (__i) < (__state)->num_private_objs; (__i)++) \
+		for_each_if(__drm_dp_mst_state_iter_get((__state), &(mgr), NULL,
&(new_state), (__i)))
+
 #endif
-- 
2.19.1

There has been a TODO waiting for quite a long time in
drm_dp_mst_topology.c:

	/* We cannot rely on port->vcpi.num_slots to update
	 * topology_state->avail_slots as the port may not exist if the parent
	 * branch device was unplugged. This should be fixed by tracking
	 * per-port slot allocation in drm_dp_mst_topology_state instead of
	 * depending on the caller to tell us how many slots to release.
	 */

That's not the only reason we should fix this: forcing the driver to
track the VCPI allocations throughout a state's atomic check is
error prone, because it means that extra care has to be taken with the
order that drm_dp_atomic_find_vcpi_slots() and
drm_dp_atomic_release_vcpi_slots() are called in in order to ensure
idempotency. Currently the only driver actually using these helpers,
i915, doesn't even do this correctly: multiple ->best_encoder() checks
with i915's current implementation would not be idempotent and would
over-allocate VCPI slots, something I learned trying to implement
fallback retraining in MST.

So: simplify this whole mess, and teach drm_dp_atomic_find_vcpi_slots()
and drm_dp_atomic_release_vcpi_slots() to track the VCPI allocations for
each port. This allows us to ensure idempotency without having to rely
on the driver as much. Additionally: the driver doesn't need to do any
kind of VCPI slot tracking anymore if it doesn't need it for it's own
internal state.

Additionally; this adds a new drm_dp_mst_atomic_check() helper which
must be used by atomic drivers to perform validity checks for the new
VCPI allocations incurred by a state.

Also: update the documentation and make it more obvious that these
/must/ be called by /all/ atomic drivers supporting MST.

Changes since v2:
 - Use kmemdup() for duplicating MST state - danvet
 - Move port validation out of duplicate state callback - danvet
 - Handle looping through MST topology states in
   drm_dp_mst_atomic_check() so the driver doesn't have to do it
 - Fix documentation in drm_dp_atomic_find_vcpi_slots()
 - Move the atomic check for each individual topology state into it's
   own function, reduces indenting
 - Don't consider "stale" MST ports when calculating the bandwidth
   requirements. This is needed because originally we relied on the
   state duplication functions to prune any stale ports from the new
   state, which would prevent us from incorrectly considering their
   bandwidth requirements alongside legitimate new payloads.
 - Add function references in drm_dp_atomic_release_vcpi_slots() - danvet
 - Annotate atomic VCPI and atomic check functions with __must_check
   - danvet

Changes since v1:
 - Don't use the now-removed ->atomic_check() for private objects hook,
   just give drivers a function to call themselves

Signed-off-by: Lyude Paul <lyude at redhat.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 222 ++++++++++++++++++++++----
 drivers/gpu/drm/i915/intel_display.c  |   4 +
 drivers/gpu/drm/i915/intel_dp_mst.c   |  31 ++--
 include/drm/drm_dp_mst_helper.h       |  23 ++-
 4 files changed, 225 insertions(+), 55 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
b/drivers/gpu/drm/drm_dp_mst_topology.c
index 8c3cfac437f4..74823afb262e 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2614,21 +2614,34 @@ static int drm_dp_init_vcpi(struct
drm_dp_mst_topology_mgr *mgr,
 }
 
 /**
- * drm_dp_atomic_find_vcpi_slots() - Find and add vcpi slots to the state
+ * drm_dp_atomic_find_vcpi_slots() - Find and add VCPI slots to the state
  * @state: global atomic state
  * @mgr: MST topology manager for the port
  * @port: port to find vcpi slots for
  * @pbn: bandwidth required for the mode in PBN
  *
- * RETURNS:
- * Total slots in the atomic state assigned for this port or error
+ * Allocates VCPI slots to @port, replacing any previous VCPI allocations it
+ * may have had. Any atomic drivers which support MST must call this function
+ * in their &drm_encoder_helper_funcs.atomic_check() callback to change the
+ * current VCPI allocation for the new state. The allocations are not checked
+ * against the bandwidth restraints of @mgr until the driver calls
+ * drm_dp_mst_atomic_check().
+ *
+ * See also:
+ * drm_dp_atomic_release_vcpi_slots()
+ * drm_dp_mst_atomic_check()
+ *
+ * Returns:
+ * Total slots in the atomic state assigned for this port, or a negative error
+ * code if the port no longer exists
  */
 int drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
 				  struct drm_dp_mst_topology_mgr *mgr,
 				  struct drm_dp_mst_port *port, int pbn)
 {
 	struct drm_dp_mst_topology_state *topology_state;
-	int req_slots;
+	struct drm_dp_vcpi_allocation *pos, *vcpi = NULL;
+	int prev_slots, req_slots, ret;
 
 	topology_state = drm_atomic_get_mst_topology_state(state, mgr);
 	if (IS_ERR(topology_state))
@@ -2637,20 +2650,41 @@ int drm_dp_atomic_find_vcpi_slots(struct
drm_atomic_state *state,
 	port = drm_dp_get_validated_port_ref(mgr, port);
 	if (port == NULL)
 		return -EINVAL;
-	req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
-	DRM_DEBUG_KMS("vcpi slots req=%d, avail=%d\n",
-			req_slots, topology_state->avail_slots);
 
-	if (req_slots > topology_state->avail_slots) {
-		drm_dp_put_port(port);
-		return -ENOSPC;
+	/* Find the current allocation for this port, if any */
+	list_for_each_entry(pos, &topology_state->vcpis, next) {
+		if (pos->port == port) {
+			vcpi = pos;
+			prev_slots = vcpi->vcpi;
+			break;
+		}
 	}
+	if (!vcpi)
+		prev_slots = 0;
+
+	req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
 
-	topology_state->avail_slots -= req_slots;
-	DRM_DEBUG_KMS("vcpi slots avail=%d",
topology_state->avail_slots);
+	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] [MST PORT:%p] vcpi %d -> %d\n",
+		      port->connector->base.id, port->connector->name, port,
+		      prev_slots, req_slots);
 
+	/* Add the new allocation to the state */
+	if (!vcpi) {
+		vcpi = kzalloc(sizeof(*vcpi), GFP_KERNEL);
+		if (!vcpi) {
+			ret = -ENOMEM;
+			goto out;
+		}
+
+		vcpi->port = port;
+		list_add(&vcpi->next, &topology_state->vcpis);
+	}
+	vcpi->vcpi = req_slots;
+
+	ret = req_slots;
+out:
 	drm_dp_put_port(port);
-	return req_slots;
+	return ret;
 }
 EXPORT_SYMBOL(drm_dp_atomic_find_vcpi_slots);
 
@@ -2658,32 +2692,50 @@ EXPORT_SYMBOL(drm_dp_atomic_find_vcpi_slots);
  * drm_dp_atomic_release_vcpi_slots() - Release allocated vcpi slots
  * @state: global atomic state
  * @mgr: MST topology manager for the port
- * @slots: number of vcpi slots to release
+ * @port: The port to release the VCPI slots from
  *
- * RETURNS:
- * 0 if @slots were added back to
&drm_dp_mst_topology_state->avail_slots or
- * negative error code
+ * Releases any VCPI slots that have been allocated to a port in the atomic
+ * state. Any atomic drivers which support MST must call this function in
+ * their &drm_connector_helper_funcs.atomic_check() callback when the
+ * connector will no longer have VCPI allocated (e.g. because it's CRTC was
+ * removed).
+ *
+ * It is OK to call this even if @port has been removed from the system, in
+ * which case it will just amount to a no-op.
+ *
+ * See also:
+ * drm_dp_atomic_find_vcpi_slots()
+ * drm_dp_mst_atomic_check()
+ *
+ * Returns:
+ * 0 if all slots for this port were added back to
+ * &drm_dp_mst_topology_state.avail_slots or negative error code
  */
 int drm_dp_atomic_release_vcpi_slots(struct drm_atomic_state *state,
 				     struct drm_dp_mst_topology_mgr *mgr,
-				     int slots)
+				     struct drm_dp_mst_port *port)
 {
 	struct drm_dp_mst_topology_state *topology_state;
+	struct drm_dp_vcpi_allocation *tmp, *pos;
 
 	topology_state = drm_atomic_get_mst_topology_state(state, mgr);
 	if (IS_ERR(topology_state))
 		return PTR_ERR(topology_state);
 
-	/* We cannot rely on port->vcpi.num_slots to update
-	 * topology_state->avail_slots as the port may not exist if the parent
-	 * branch device was unplugged. This should be fixed by tracking
-	 * per-port slot allocation in drm_dp_mst_topology_state instead of
-	 * depending on the caller to tell us how many slots to release.
-	 */
-	topology_state->avail_slots += slots;
-	DRM_DEBUG_KMS("vcpi slots released=%d, avail=%d\n",
-			slots, topology_state->avail_slots);
+	list_for_each_entry_safe(pos, tmp, &topology_state->vcpis, next) {
+		if (pos->port == port) {
+			list_del(&pos->next);
+			DRM_DEBUG_KMS("[MST PORT:%p] vcpi %d -> 0\n",
+				      port, pos->vcpi);
 
+			kfree(pos);
+			return 0;
+		}
+	}
+
+	/* If no allocation was found, all that means is that the port was
+	 * destroyed since the last atomic commit. That's OK!
+	 */
 	return 0;
 }
 EXPORT_SYMBOL(drm_dp_atomic_release_vcpi_slots);
@@ -3112,15 +3164,34 @@ static void drm_dp_destroy_connector_work(struct
work_struct *work)
 static struct drm_private_state *
 drm_dp_mst_duplicate_state(struct drm_private_obj *obj)
 {
-	struct drm_dp_mst_topology_state *state;
+	struct drm_dp_mst_topology_state *state, *old_state +	
to_dp_mst_topology_state(obj->state);
+	struct drm_dp_vcpi_allocation *pos, *vcpi;
 
-	state = kmemdup(obj->state, sizeof(*state), GFP_KERNEL);
+	state = kmemdup(old_state, sizeof(*state), GFP_KERNEL);
 	if (!state)
 		return NULL;
 
 	__drm_atomic_helper_private_obj_duplicate_state(obj, &state->base);
 
+	INIT_LIST_HEAD(&state->vcpis);
+
+	list_for_each_entry(pos, &old_state->vcpis, next) {
+		vcpi = kmemdup(pos, sizeof(*vcpi), GFP_KERNEL);
+		if (!vcpi)
+			goto fail_alloc;
+
+		list_add(&vcpi->next, &state->vcpis);
+	}
+
 	return &state->base;
+
+fail_alloc:
+	list_for_each_entry_safe(pos, vcpi, &state->vcpis, next)
+		kfree(pos);
+	kfree(state);
+
+	return NULL;
 }
 
 static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
@@ -3128,14 +3199,99 @@ static void drm_dp_mst_destroy_state(struct
drm_private_obj *obj,
 {
 	struct drm_dp_mst_topology_state *mst_state  	
to_dp_mst_topology_state(state);
+	struct drm_dp_vcpi_allocation *pos, *tmp;
+
+	list_for_each_entry_safe(pos, tmp, &mst_state->vcpis, next)
+		kfree(pos);
 
 	kfree(mst_state);
 }
 
-static const struct drm_private_state_funcs mst_state_funcs = {
+static inline int
+drm_dp_mst_atomic_check_topology_state(struct drm_dp_mst_topology_mgr *mgr,
+				       struct drm_dp_mst_topology_state *mst_state)
+{
+	struct drm_dp_vcpi_allocation *vcpi;
+	struct drm_dp_mst_port *port;
+	int avail_slots = 63, ret;
+
+	list_for_each_entry(vcpi, &mst_state->vcpis, next) {
+		/* Ports that no longer exist shouldn't be counted towards the
+		 * bandwidth requirements for the state, so skip them
+		 */
+		port = drm_dp_get_validated_port_ref(mgr, vcpi->port);
+		if (!port) {
+			DRM_DEBUG_ATOMIC("[MST PORT:%p] is stale, skipping checks\n",
+					 vcpi->port);
+			continue;
+		}
+
+		DRM_DEBUG_ATOMIC("[MST PORT:%p] requires %d vcpi slots\n",
+				 vcpi->port, vcpi->vcpi);
+
+		avail_slots -= vcpi->vcpi;
+		if (avail_slots < 0) {
+			DRM_DEBUG_ATOMIC("[MST PORT:%p] not enough vcpi slots in mst_state %p
(avail=%d)\n",
+					 vcpi->port, mst_state,
+					 avail_slots + vcpi->vcpi);
+			ret = -ENOSPC;
+			goto port_fail;
+		}
+
+		drm_dp_put_port(port);
+	}
+	DRM_DEBUG_ATOMIC("[MST MGR:%p] mst_state %p vcpi avail=%d
used=%d\n",
+			 mgr, mst_state, avail_slots,
+			 63 - avail_slots);
+
+	return 0;
+port_fail:
+	drm_dp_put_port(port);
+	return ret;
+}
+
+/**
+ * drm_dp_mst_atomic_check - Check that the new state of an MST topology in an
+ * atomic update is valid
+ * @state: Pointer to the new &struct drm_dp_mst_topology_state
+ *
+ * Checks the given topology state for an atomic update to ensure that it's
+ * valid. This includes checking whether there's enough bandwidth to
support
+ * the new VCPI allocations in the atomic update.
+ *
+ * Any atomic drivers supporting DP MST must make sure to call this after
+ * checking the rest of their state in their
+ * &drm_mode_config_funcs.atomic_check() callback.
+ *
+ * See also:
+ * drm_dp_atomic_find_vcpi_slots()
+ * drm_dp_atomic_release_vcpi_slots()
+ *
+ * Returns:
+ *
+ * 0 if the new state is valid, negative error code otherwise.
+ */
+int drm_dp_mst_atomic_check(struct drm_atomic_state *state)
+{
+	struct drm_dp_mst_topology_mgr *mgr;
+	struct drm_dp_mst_topology_state *mst_state;
+	int i, ret = 0;
+
+	for_each_new_mst_mgr_in_state(state, mgr, mst_state, i) {
+		ret = drm_dp_mst_atomic_check_topology_state(mgr, mst_state);
+		if (ret)
+			break;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(drm_dp_mst_atomic_check);
+
+const struct drm_private_state_funcs drm_dp_mst_topology_state_funcs = {
 	.atomic_duplicate_state = drm_dp_mst_duplicate_state,
 	.atomic_destroy_state = drm_dp_mst_destroy_state,
 };
+EXPORT_SYMBOL(drm_dp_mst_topology_state_funcs);
 
 /**
  * drm_atomic_get_mst_topology_state: get MST topology state
@@ -3213,13 +3369,11 @@ int drm_dp_mst_topology_mgr_init(struct
drm_dp_mst_topology_mgr *mgr,
 		return -ENOMEM;
 
 	mst_state->mgr = mgr;
-
-	/* max. time slots - one slot for MTP header */
-	mst_state->avail_slots = 63;
+	INIT_LIST_HEAD(&mst_state->vcpis);
 
 	drm_atomic_private_obj_init(&mgr->base,
 				    &mst_state->base,
-				    &mst_state_funcs);
+				    &drm_dp_mst_topology_state_funcs);
 
 	return 0;
 }
diff --git a/drivers/gpu/drm/i915/intel_display.c
b/drivers/gpu/drm/i915/intel_display.c
index bbf8ca21a7a2..8749cf61a6ac 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -12553,6 +12553,10 @@ static int intel_atomic_check(struct drm_device *dev,
 				       "[modeset]" : "[fastset]");
 	}
 
+	ret = drm_dp_mst_atomic_check(state);
+	if (ret)
+		return ret;
+
 	if (any_ms) {
 		ret = intel_modeset_checks(state);
 
diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c
b/drivers/gpu/drm/i915/intel_dp_mst.c
index 8b71d64ebd9d..aaf904738b78 100644
--- a/drivers/gpu/drm/i915/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/intel_dp_mst.c
@@ -114,28 +114,31 @@ static int intel_dp_mst_atomic_check(struct drm_connector
*connector,
 	struct drm_connector_state *old_conn_state;
 	struct drm_crtc *old_crtc;
 	struct drm_crtc_state *crtc_state;
-	int slots, ret = 0;
+	struct intel_connector *intel_connector +		to_intel_connector(connector);
+	struct drm_dp_mst_topology_mgr *mgr +	
&intel_connector->mst_port->mst_mgr;
+	struct drm_dp_mst_port *port = intel_connector->port;
+	int ret = 0;
 
 	old_conn_state = drm_atomic_get_old_connector_state(state, connector);
 	old_crtc = old_conn_state->crtc;
 	if (!old_crtc)
 		return ret;
 
-	crtc_state = drm_atomic_get_new_crtc_state(state, old_crtc);
-	slots = to_intel_crtc_state(crtc_state)->dp_m_n.tu;
-	if (drm_atomic_crtc_needs_modeset(crtc_state) && slots > 0) {
-		struct drm_dp_mst_topology_mgr *mgr;
-		struct drm_encoder *old_encoder;
+	/* Free VCPI, since compute_config() won't be run */
+	if (!new_conn_state->crtc) {
+		crtc_state = drm_atomic_get_new_crtc_state(state, old_crtc);
 
-		old_encoder = old_conn_state->best_encoder;
-		mgr = &enc_to_mst(old_encoder)->primary->dp.mst_mgr;
-
-		ret = drm_dp_atomic_release_vcpi_slots(state, mgr, slots);
-		if (ret)
-			DRM_DEBUG_KMS("failed releasing %d vcpi slots:%d\n", slots, ret);
-		else
-			to_intel_crtc_state(crtc_state)->dp_m_n.tu = 0;
+		ret = drm_dp_atomic_release_vcpi_slots(state, mgr, port);
+		if (ret) {
+			DRM_DEBUG_KMS("failed releasing vcpi slots: %d\n",
+				      ret);
+			return ret;
+		}
+		to_intel_crtc_state(crtc_state)->dp_m_n.tu = 0;
 	}
+
 	return ret;
 }
 
diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
index 3faceb66f5cb..08b67948b8f9 100644
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -406,9 +406,15 @@ struct drm_dp_payload {
 
 #define to_dp_mst_topology_state(x) container_of(x, struct
drm_dp_mst_topology_state, base)
 
+struct drm_dp_vcpi_allocation {
+	struct drm_dp_mst_port *port;
+	int vcpi;
+	struct list_head next;
+};
+
 struct drm_dp_mst_topology_state {
 	struct drm_private_state base;
-	int avail_slots;
+	struct list_head vcpis;
 	struct drm_dp_mst_topology_mgr *mgr;
 };
 
@@ -619,14 +625,17 @@ void drm_dp_mst_topology_mgr_suspend(struct
drm_dp_mst_topology_mgr *mgr);
 int drm_dp_mst_topology_mgr_resume(struct drm_dp_mst_topology_mgr *mgr);
 struct drm_dp_mst_topology_state *drm_atomic_get_mst_topology_state(struct
drm_atomic_state *state,
 								    struct drm_dp_mst_topology_mgr *mgr);
-int drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
-				  struct drm_dp_mst_topology_mgr *mgr,
-				  struct drm_dp_mst_port *port, int pbn);
-int drm_dp_atomic_release_vcpi_slots(struct drm_atomic_state *state,
-				     struct drm_dp_mst_topology_mgr *mgr,
-				     int slots);
+int __must_check
+drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
+			      struct drm_dp_mst_topology_mgr *mgr,
+			      struct drm_dp_mst_port *port, int pbn);
+int __must_check
+drm_dp_atomic_release_vcpi_slots(struct drm_atomic_state *state,
+				 struct drm_dp_mst_topology_mgr *mgr,
+				 struct drm_dp_mst_port *port);
 int drm_dp_send_power_updown_phy(struct drm_dp_mst_topology_mgr *mgr,
 				 struct drm_dp_mst_port *port, bool power_up);
+int __must_check drm_dp_mst_atomic_check(struct drm_atomic_state *state);
 
 extern const struct drm_private_state_funcs drm_dp_mst_topology_state_funcs;
 
-- 
2.19.1

It occurred to me that we never actually check this! So let's start
doing that.

Signed-off-by: Lyude Paul <lyude at redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
b/drivers/gpu/drm/drm_dp_mst_topology.c
index 74823afb262e..8ef0c5f5c7cf 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -3213,7 +3213,7 @@ drm_dp_mst_atomic_check_topology_state(struct
drm_dp_mst_topology_mgr *mgr,
 {
 	struct drm_dp_vcpi_allocation *vcpi;
 	struct drm_dp_mst_port *port;
-	int avail_slots = 63, ret;
+	int avail_slots = 63, payload_count = 0, ret;
 
 	list_for_each_entry(vcpi, &mst_state->vcpis, next) {
 		/* Ports that no longer exist shouldn't be counted towards the
@@ -3238,6 +3238,13 @@ drm_dp_mst_atomic_check_topology_state(struct
drm_dp_mst_topology_mgr *mgr,
 			goto port_fail;
 		}
 
+		if (++payload_count > mgr->max_payloads) {
+			DRM_DEBUG_ATOMIC("[MST MGR:%p] state %p has too many payloads
(max=%d)\n",
+					 mgr, mst_state, mgr->max_payloads);
+			ret = -EINVAL;
+			goto port_fail;
+		}
+
 		drm_dp_put_port(port);
 	}
 	DRM_DEBUG_ATOMIC("[MST MGR:%p] mst_state %p vcpi avail=%d
used=%d\n",
-- 
2.19.1

Currently, nouveau uses the yolo method of setting up MST displays: it
uses the old VCPI helpers (drm_dp_find_vcpi_slots()) for computing the
display configuration. These helpers don't take care to make sure they
take a reference to the mstb port that they're checking, and
additionally don't actually check whether or not the topology still has
enough bandwidth to provide the VCPI tokens required.

So, drop usage of the old helpers and move entirely over to the atomic
helpers.

Signed-off-by: Lyude Paul <lyude at redhat.com>
Acked-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 drivers/gpu/drm/nouveau/dispnv50/disp.c | 50 +++++++++++++++++++++----
 1 file changed, 43 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c
b/drivers/gpu/drm/nouveau/dispnv50/disp.c
index 6cbbae3f438b..0469ef9e1a54 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -747,16 +747,22 @@ nv50_msto_atomic_check(struct drm_encoder *encoder,
 		       struct drm_crtc_state *crtc_state,
 		       struct drm_connector_state *conn_state)
 {
-	struct nv50_mstc *mstc = nv50_mstc(conn_state->connector);
+	struct drm_atomic_state *state = crtc_state->state;
+	struct drm_connector *connector = conn_state->connector;
+	struct nv50_mstc *mstc = nv50_mstc(connector);
 	struct nv50_mstm *mstm = mstc->mstm;
-	int bpp = conn_state->connector->display_info.bpc * 3;
+	int bpp = connector->display_info.bpc * 3;
 	int slots;
 
-	mstc->pbn = drm_dp_calc_pbn_mode(crtc_state->adjusted_mode.clock, bpp);
-
-	slots = drm_dp_find_vcpi_slots(&mstm->mgr, mstc->pbn);
-	if (slots < 0)
-		return slots;
+	mstc->pbn = drm_dp_calc_pbn_mode(crtc_state->adjusted_mode.clock,
+					 bpp);
+	/* Zombies don't need VCPI */
+	if (!drm_connector_is_unregistered(connector)) {
+		slots = drm_dp_atomic_find_vcpi_slots(state, &mstm->mgr,
+						      mstc->port, mstc->pbn);
+		if (slots < 0)
+			return slots;
+	}
 
 	return nv50_outp_atomic_check_view(encoder, crtc_state, conn_state,
 					   mstc->native);
@@ -920,12 +926,38 @@ nv50_mstc_get_modes(struct drm_connector *connector)
 	return ret;
 }
 
+static int
+nv50_mstc_atomic_check(struct drm_connector *connector,
+		       struct drm_connector_state *new_conn_state)
+{
+	struct drm_atomic_state *state = new_conn_state->state;
+	struct nv50_mstc *mstc = nv50_mstc(connector);
+	struct drm_dp_mst_topology_mgr *mgr = &mstc->mstm->mgr;
+	struct drm_connector_state *old_conn_state;
+	struct drm_crtc *old_crtc;
+
+	old_conn_state = drm_atomic_get_old_connector_state(state, connector);
+	old_crtc = old_conn_state->crtc;
+
+	/* We only need to release VCPI here if we're going from having a CRTC
+	 * on this connector, to not having one
+	 */
+	if (!old_crtc || new_conn_state->crtc)
+		return 0;
+
+	/* Release the previous VCPI allocation since the encoder's
+	 * atomic_check() won't be called
+	 */
+	return drm_dp_atomic_release_vcpi_slots(state, mgr, mstc->port);
+}
+
 static const struct drm_connector_helper_funcs
 nv50_mstc_help = {
 	.get_modes = nv50_mstc_get_modes,
 	.mode_valid = nv50_mstc_mode_valid,
 	.best_encoder = nv50_mstc_best_encoder,
 	.atomic_best_encoder = nv50_mstc_atomic_best_encoder,
+	.atomic_check = nv50_mstc_atomic_check,
 };
 
 static enum drm_connector_status
@@ -2109,6 +2141,10 @@ nv50_disp_atomic_check(struct drm_device *dev, struct
drm_atomic_state *state)
 			return ret;
 	}
 
+	ret = drm_dp_mst_atomic_check(state);
+	if (ret)
+		return ret;
+
 	return 0;
 }
 
-- 
2.19.1

Same thing we did in i915, but for nouveau now.

Signed-off-by: Lyude Paul <lyude at redhat.com>
Cc: Daniel Vetter <daniel at ffwll.ch>
---
 drivers/gpu/drm/nouveau/dispnv50/disp.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c
b/drivers/gpu/drm/nouveau/dispnv50/disp.c
index 0469ef9e1a54..ff04a56b5949 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -698,8 +698,10 @@ nv50_msto_cleanup(struct nv50_msto *msto)
 	struct nv50_mstm *mstm = mstc->mstm;
 
 	NV_ATOMIC(drm, "%s: msto cleanup\n", msto->encoder.name);
-	if (mstc->port && mstc->port->vcpi.vcpi > 0 &&
!nv50_msto_payload(msto))
+	if (!drm_connector_is_unregistered(&mstc->connector) &&
+	    mstc->port->vcpi.vcpi > 0 && !nv50_msto_payload(msto))
 		drm_dp_mst_deallocate_vcpi(&mstm->mgr, mstc->port);
+
 	if (msto->disabled) {
 		msto->mstc = NULL;
 		msto->head = NULL;
@@ -725,7 +727,8 @@ nv50_msto_prepare(struct nv50_msto *msto)
 	};
 
 	NV_ATOMIC(drm, "%s: msto prepare\n", msto->encoder.name);
-	if (mstc->port && mstc->port->vcpi.vcpi > 0) {
+	if (!drm_connector_is_unregistered(&mstc->connector) &&
+	    mstc->port->vcpi.vcpi > 0) {
 		struct drm_dp_payload *payload = nv50_msto_payload(msto);
 		if (payload) {
 			args.vcpi.start_slot = payload->start_slot;
@@ -828,7 +831,7 @@ nv50_msto_disable(struct drm_encoder *encoder)
 	struct nv50_mstc *mstc = msto->mstc;
 	struct nv50_mstm *mstm = mstc->mstm;
 
-	if (mstc->port)
+	if (!drm_connector_is_unregistered(&mstc->connector))
 		drm_dp_mst_reset_vcpi_slots(&mstm->mgr, mstc->port);
 
 	mstm->outp->update(mstm->outp, msto->head->base.index, NULL, 0,
0);
@@ -967,7 +970,7 @@ nv50_mstc_detect(struct drm_connector *connector, bool
force)
 	enum drm_connector_status conn_status;
 	int ret;
 
-	if (!mstc->port)
+	if (drm_connector_is_unregistered(&mstc->connector))
 		return connector_status_disconnected;
 
 	ret = pm_runtime_get_sync(connector->dev->dev);
@@ -1105,10 +1108,6 @@ nv50_mstm_destroy_connector(struct
drm_dp_mst_topology_mgr *mgr,
 
 	drm_fb_helper_remove_one_connector(&drm->fbcon->helper,
&mstc->connector);
 
-	drm_modeset_lock(&drm->dev->mode_config.connection_mutex, NULL);
-	mstc->port = NULL;
-	drm_modeset_unlock(&drm->dev->mode_config.connection_mutex);
-
 	drm_connector_put(&mstc->connector);
 }
 
-- 
2.19.1

On Tue, Nov 06, 2018 at 08:21:14PM -0500, Lyude Paul
wrote:
> There has been a TODO waiting for quite a long time in
> drm_dp_mst_topology.c:
> 
> 	/* We cannot rely on port->vcpi.num_slots to update
> 	 * topology_state->avail_slots as the port may not exist if the parent
> 	 * branch device was unplugged. This should be fixed by tracking
> 	 * per-port slot allocation in drm_dp_mst_topology_state instead of
> 	 * depending on the caller to tell us how many slots to release.
> 	 */
> 
> That's not the only reason we should fix this: forcing the driver to
> track the VCPI allocations throughout a state's atomic check is
> error prone, because it means that extra care has to be taken with the
> order that drm_dp_atomic_find_vcpi_slots() and
> drm_dp_atomic_release_vcpi_slots() are called in in order to ensure
> idempotency. Currently the only driver actually using these helpers,
> i915, doesn't even do this correctly: multiple ->best_encoder()
checks
> with i915's current implementation would not be idempotent and would
> over-allocate VCPI slots, something I learned trying to implement
> fallback retraining in MST.
> 
> So: simplify this whole mess, and teach drm_dp_atomic_find_vcpi_slots()
> and drm_dp_atomic_release_vcpi_slots() to track the VCPI allocations for
> each port. This allows us to ensure idempotency without having to rely
> on the driver as much. Additionally: the driver doesn't need to do any
> kind of VCPI slot tracking anymore if it doesn't need it for it's
own
> internal state.
> 
> Additionally; this adds a new drm_dp_mst_atomic_check() helper which
> must be used by atomic drivers to perform validity checks for the new
> VCPI allocations incurred by a state.
> 
> Also: update the documentation and make it more obvious that these
> /must/ be called by /all/ atomic drivers supporting MST.
> 
> Changes since v2:
>  - Use kmemdup() for duplicating MST state - danvet
>  - Move port validation out of duplicate state callback - danvet
>  - Handle looping through MST topology states in
>    drm_dp_mst_atomic_check() so the driver doesn't have to do it
>  - Fix documentation in drm_dp_atomic_find_vcpi_slots()
>  - Move the atomic check for each individual topology state into it's
>    own function, reduces indenting
>  - Don't consider "stale" MST ports when calculating the
bandwidth
>    requirements. This is needed because originally we relied on the
>    state duplication functions to prune any stale ports from the new
>    state, which would prevent us from incorrectly considering their
>    bandwidth requirements alongside legitimate new payloads.
>  - Add function references in drm_dp_atomic_release_vcpi_slots() - danvet
>  - Annotate atomic VCPI and atomic check functions with __must_check
>    - danvet
> 
> Changes since v1:
>  - Don't use the now-removed ->atomic_check() for private objects
hook,
>    just give drivers a function to call themselves
> 
> Signed-off-by: Lyude Paul <lyude at redhat.com>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 222 ++++++++++++++++++++++----
>  drivers/gpu/drm/i915/intel_display.c  |   4 +
>  drivers/gpu/drm/i915/intel_dp_mst.c   |  31 ++--
>  include/drm/drm_dp_mst_helper.h       |  23 ++-
>  4 files changed, 225 insertions(+), 55 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 8c3cfac437f4..74823afb262e 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -2614,21 +2614,34 @@ static int drm_dp_init_vcpi(struct
drm_dp_mst_topology_mgr *mgr,
>  }
>  
>  /**
> - * drm_dp_atomic_find_vcpi_slots() - Find and add vcpi slots to the state
> + * drm_dp_atomic_find_vcpi_slots() - Find and add VCPI slots to the state
>   * @state: global atomic state
>   * @mgr: MST topology manager for the port
>   * @port: port to find vcpi slots for
>   * @pbn: bandwidth required for the mode in PBN
>   *
> - * RETURNS:
> - * Total slots in the atomic state assigned for this port or error
> + * Allocates VCPI slots to @port, replacing any previous VCPI allocations
it
> + * may have had. Any atomic drivers which support MST must call this
function
> + * in their &drm_encoder_helper_funcs.atomic_check() callback to
change the
> + * current VCPI allocation for the new state. The allocations are not
checked
> + * against the bandwidth restraints of @mgr until the driver calls
> + * drm_dp_mst_atomic_check().
> + *
> + * See also:
> + * drm_dp_atomic_release_vcpi_slots()
> + * drm_dp_mst_atomic_check()
> + *
> + * Returns:
> + * Total slots in the atomic state assigned for this port, or a negative
error
> + * code if the port no longer exists
>   */
>  int drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
>  				  struct drm_dp_mst_topology_mgr *mgr,
>  				  struct drm_dp_mst_port *port, int pbn)
>  {
>  	struct drm_dp_mst_topology_state *topology_state;
> -	int req_slots;
> +	struct drm_dp_vcpi_allocation *pos, *vcpi = NULL;
> +	int prev_slots, req_slots, ret;
>  
>  	topology_state = drm_atomic_get_mst_topology_state(state, mgr);
>  	if (IS_ERR(topology_state))
> @@ -2637,20 +2650,41 @@ int drm_dp_atomic_find_vcpi_slots(struct
drm_atomic_state *state,
>  	port = drm_dp_get_validated_port_ref(mgr, port);
>  	if (port == NULL)
>  		return -EINVAL;
> -	req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
> -	DRM_DEBUG_KMS("vcpi slots req=%d, avail=%d\n",
> -			req_slots, topology_state->avail_slots);
>  
> -	if (req_slots > topology_state->avail_slots) {
> -		drm_dp_put_port(port);
> -		return -ENOSPC;
> +	/* Find the current allocation for this port, if any */
> +	list_for_each_entry(pos, &topology_state->vcpis, next) {
> +		if (pos->port == port) {
> +			vcpi = pos;
> +			prev_slots = vcpi->vcpi;
> +			break;
> +		}
>  	}
> +	if (!vcpi)
> +		prev_slots = 0;
> +
> +	req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
>  
> -	topology_state->avail_slots -= req_slots;
> -	DRM_DEBUG_KMS("vcpi slots avail=%d",
topology_state->avail_slots);
> +	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] [MST PORT:%p] vcpi %d ->
%d\n",
> +		      port->connector->base.id, port->connector->name, port,
> +		      prev_slots, req_slots);
>  
> +	/* Add the new allocation to the state */
> +	if (!vcpi) {
> +		vcpi = kzalloc(sizeof(*vcpi), GFP_KERNEL);
> +		if (!vcpi) {
> +			ret = -ENOMEM;
> +			goto out;
> +		}
> +
> +		vcpi->port = port;
> +		list_add(&vcpi->next, &topology_state->vcpis);
> +	}
> +	vcpi->vcpi = req_slots;
> +
> +	ret = req_slots;
> +out:
>  	drm_dp_put_port(port);
> -	return req_slots;
> +	return ret;
>  }
>  EXPORT_SYMBOL(drm_dp_atomic_find_vcpi_slots);
>  
> @@ -2658,32 +2692,50 @@ EXPORT_SYMBOL(drm_dp_atomic_find_vcpi_slots);
>   * drm_dp_atomic_release_vcpi_slots() - Release allocated vcpi slots
>   * @state: global atomic state
>   * @mgr: MST topology manager for the port
> - * @slots: number of vcpi slots to release
> + * @port: The port to release the VCPI slots from
>   *
> - * RETURNS:
> - * 0 if @slots were added back to
&drm_dp_mst_topology_state->avail_slots or
> - * negative error code
> + * Releases any VCPI slots that have been allocated to a port in the
atomic
> + * state. Any atomic drivers which support MST must call this function in
> + * their &drm_connector_helper_funcs.atomic_check() callback when the
> + * connector will no longer have VCPI allocated (e.g. because it's
CRTC was
> + * removed).
> + *
> + * It is OK to call this even if @port has been removed from the system,
in
> + * which case it will just amount to a no-op.
> + *
> + * See also:
> + * drm_dp_atomic_find_vcpi_slots()
> + * drm_dp_mst_atomic_check()
> + *
> + * Returns:
> + * 0 if all slots for this port were added back to
> + * &drm_dp_mst_topology_state.avail_slots or negative error code
>   */
>  int drm_dp_atomic_release_vcpi_slots(struct drm_atomic_state *state,
>  				     struct drm_dp_mst_topology_mgr *mgr,
> -				     int slots)
> +				     struct drm_dp_mst_port *port)
>  {
>  	struct drm_dp_mst_topology_state *topology_state;
> +	struct drm_dp_vcpi_allocation *tmp, *pos;
>  
>  	topology_state = drm_atomic_get_mst_topology_state(state, mgr);
>  	if (IS_ERR(topology_state))
>  		return PTR_ERR(topology_state);
>  
> -	/* We cannot rely on port->vcpi.num_slots to update
> -	 * topology_state->avail_slots as the port may not exist if the parent
> -	 * branch device was unplugged. This should be fixed by tracking
> -	 * per-port slot allocation in drm_dp_mst_topology_state instead of
> -	 * depending on the caller to tell us how many slots to release.
> -	 */
> -	topology_state->avail_slots += slots;
> -	DRM_DEBUG_KMS("vcpi slots released=%d, avail=%d\n",
> -			slots, topology_state->avail_slots);
> +	list_for_each_entry_safe(pos, tmp, &topology_state->vcpis, next) {
> +		if (pos->port == port) {
> +			list_del(&pos->next);
> +			DRM_DEBUG_KMS("[MST PORT:%p] vcpi %d -> 0\n",
> +				      port, pos->vcpi);
>  
> +			kfree(pos);
> +			return 0;
> +		}
> +	}
> +
> +	/* If no allocation was found, all that means is that the port was
> +	 * destroyed since the last atomic commit. That's OK!
> +	 */
This case here has me a bit worried. I thought with your changes we'll
always have the port pointer still around, to be able to clean things up
properly. If this is not the case then we'd potentially leak the vcpi
allocation for an unplugged port.

Otoh if the driver releases the allocation for a port twice it's probably
mixed up it's own book-keeping. We should WARN about that case.

This is kinda fallout from your change to not prune allocations on
duplicate, and I think will further clean up how this is handled.

So with the comment removed and replaced by a WARNING(1,"no vcpi
allocation found for port %p\n", port) or something like that this should
be solid.

>  	return 0;
>  }
>  EXPORT_SYMBOL(drm_dp_atomic_release_vcpi_slots);
> @@ -3112,15 +3164,34 @@ static void drm_dp_destroy_connector_work(struct
work_struct *work)
>  static struct drm_private_state *
>  drm_dp_mst_duplicate_state(struct drm_private_obj *obj)
>  {
> -	struct drm_dp_mst_topology_state *state;
> +	struct drm_dp_mst_topology_state *state, *old_state > +	
to_dp_mst_topology_state(obj->state);
> +	struct drm_dp_vcpi_allocation *pos, *vcpi;
>  
> -	state = kmemdup(obj->state, sizeof(*state), GFP_KERNEL);
> +	state = kmemdup(old_state, sizeof(*state), GFP_KERNEL);
>  	if (!state)
>  		return NULL;
>  
>  	__drm_atomic_helper_private_obj_duplicate_state(obj,
&state->base);
>  
> +	INIT_LIST_HEAD(&state->vcpis);
> +
> +	list_for_each_entry(pos, &old_state->vcpis, next) {
> +		vcpi = kmemdup(pos, sizeof(*vcpi), GFP_KERNEL);
> +		if (!vcpi)
> +			goto fail_alloc;
> +
> +		list_add(&vcpi->next, &state->vcpis);
> +	}
> +
>  	return &state->base;
> +
> +fail_alloc:
> +	list_for_each_entry_safe(pos, vcpi, &state->vcpis, next)
> +		kfree(pos);
> +	kfree(state);
> +
> +	return NULL;
>  }
>  
>  static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
> @@ -3128,14 +3199,99 @@ static void drm_dp_mst_destroy_state(struct
drm_private_obj *obj,
>  {
>  	struct drm_dp_mst_topology_state *mst_state >  	
to_dp_mst_topology_state(state);
> +	struct drm_dp_vcpi_allocation *pos, *tmp;
> +
> +	list_for_each_entry_safe(pos, tmp, &mst_state->vcpis, next)
> +		kfree(pos);
>  
>  	kfree(mst_state);
>  }
>  
> -static const struct drm_private_state_funcs mst_state_funcs = {
> +static inline int
> +drm_dp_mst_atomic_check_topology_state(struct drm_dp_mst_topology_mgr
*mgr,
> +				       struct drm_dp_mst_topology_state *mst_state)
> +{
> +	struct drm_dp_vcpi_allocation *vcpi;
> +	struct drm_dp_mst_port *port;
> +	int avail_slots = 63, ret;
> +
> +	list_for_each_entry(vcpi, &mst_state->vcpis, next) {
> +		/* Ports that no longer exist shouldn't be counted towards the
> +		 * bandwidth requirements for the state, so skip them
> +		 */
Scenario:
- 2 mst sinks on a single host side port.
- 1st connector is active, 2nd connector is off.
- 1st connector is hot-unplugged, but userspace hasn't realized this yet,
  so not yet come around to do the disabling modeset.
- At the same time userspace decides to enable the 2nd output, which
  forces a modeset and pulls the topology state in.
- This function here decides to only look at the vcpi allocation for the
  2nd connector because the first one is gone already.
- Unfortunately lighting up both connectors at the same time isn't
  possible, because too many vcpi. But since userspace didn't ask for a
  modeset on the now unplugged first connector.
-> Modeset goes boom because we enable too many vcpi.

But with the change in how we release vcpi allocations there's no need to
ignore disconnected stuff here, and we should be able to check vcpi limits
by just checking all of them.

I didn't see anything else serious, so with the above two things resolved
this has my Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

One bikeshed below, because I need to prove I scrolled to the end :-)
> +		port = drm_dp_get_validated_port_ref(mgr, vcpi->port);
> +		if (!port) {
> +			DRM_DEBUG_ATOMIC("[MST PORT:%p] is stale, skipping checks\n",
> +					 vcpi->port);
> +			continue;
> +		}
> +
> +		DRM_DEBUG_ATOMIC("[MST PORT:%p] requires %d vcpi slots\n",
> +				 vcpi->port, vcpi->vcpi);
> +
> +		avail_slots -= vcpi->vcpi;
> +		if (avail_slots < 0) {
> +			DRM_DEBUG_ATOMIC("[MST PORT:%p] not enough vcpi slots in mst_state
%p (avail=%d)\n",
> +					 vcpi->port, mst_state,
> +					 avail_slots + vcpi->vcpi);
> +			ret = -ENOSPC;
> +			goto port_fail;
> +		}
> +
> +		drm_dp_put_port(port);
> +	}
> +	DRM_DEBUG_ATOMIC("[MST MGR:%p] mst_state %p vcpi avail=%d
used=%d\n",
> +			 mgr, mst_state, avail_slots,
> +			 63 - avail_slots);
> +
> +	return 0;
> +port_fail:
> +	drm_dp_put_port(port);
> +	return ret;
> +}
> +
> +/**
> + * drm_dp_mst_atomic_check - Check that the new state of an MST topology
in an
> + * atomic update is valid
> + * @state: Pointer to the new &struct drm_dp_mst_topology_state
> + *
> + * Checks the given topology state for an atomic update to ensure that
it's
> + * valid. This includes checking whether there's enough bandwidth to
support
> + * the new VCPI allocations in the atomic update.
> + *
> + * Any atomic drivers supporting DP MST must make sure to call this after
> + * checking the rest of their state in their
> + * &drm_mode_config_funcs.atomic_check() callback.
> + *
> + * See also:
> + * drm_dp_atomic_find_vcpi_slots()
> + * drm_dp_atomic_release_vcpi_slots()
> + *
> + * Returns:
> + *
> + * 0 if the new state is valid, negative error code otherwise.
> + */
> +int drm_dp_mst_atomic_check(struct drm_atomic_state *state)
> +{
> +	struct drm_dp_mst_topology_mgr *mgr;
> +	struct drm_dp_mst_topology_state *mst_state;
> +	int i, ret = 0;
> +
> +	for_each_new_mst_mgr_in_state(state, mgr, mst_state, i) {
> +		ret = drm_dp_mst_atomic_check_topology_state(mgr, mst_state);
> +		if (ret)
> +			break;
> +	}
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(drm_dp_mst_atomic_check);
> +
> +const struct drm_private_state_funcs drm_dp_mst_topology_state_funcs = {
>  	.atomic_duplicate_state = drm_dp_mst_duplicate_state,
>  	.atomic_destroy_state = drm_dp_mst_destroy_state,
>  };
> +EXPORT_SYMBOL(drm_dp_mst_topology_state_funcs);
>  
>  /**
>   * drm_atomic_get_mst_topology_state: get MST topology state
> @@ -3213,13 +3369,11 @@ int drm_dp_mst_topology_mgr_init(struct
drm_dp_mst_topology_mgr *mgr,
>  		return -ENOMEM;
>  
>  	mst_state->mgr = mgr;
> -
> -	/* max. time slots - one slot for MTP header */
> -	mst_state->avail_slots = 63;
> +	INIT_LIST_HEAD(&mst_state->vcpis);
>  
>  	drm_atomic_private_obj_init(&mgr->base,
>  				    &mst_state->base,
> -				    &mst_state_funcs);
> +				    &drm_dp_mst_topology_state_funcs);
>  
>  	return 0;
>  }
> diff --git a/drivers/gpu/drm/i915/intel_display.c
b/drivers/gpu/drm/i915/intel_display.c
> index bbf8ca21a7a2..8749cf61a6ac 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -12553,6 +12553,10 @@ static int intel_atomic_check(struct drm_device
*dev,
>  				       "[modeset]" : "[fastset]");
>  	}
>  
> +	ret = drm_dp_mst_atomic_check(state);
> +	if (ret)
> +		return ret;
Complete bikeshed, so feel free to ignore: I'd stuff this into
intel_modeset_checks(). Feel free to ignore.

Cheers, Daniel
> +
>  	if (any_ms) {
>  		ret = intel_modeset_checks(state);
>  
> diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c
b/drivers/gpu/drm/i915/intel_dp_mst.c
> index 8b71d64ebd9d..aaf904738b78 100644
> --- a/drivers/gpu/drm/i915/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/intel_dp_mst.c
> @@ -114,28 +114,31 @@ static int intel_dp_mst_atomic_check(struct
drm_connector *connector,
>  	struct drm_connector_state *old_conn_state;
>  	struct drm_crtc *old_crtc;
>  	struct drm_crtc_state *crtc_state;
> -	int slots, ret = 0;
> +	struct intel_connector *intel_connector > +	
to_intel_connector(connector);
> +	struct drm_dp_mst_topology_mgr *mgr > +	
&intel_connector->mst_port->mst_mgr;
> +	struct drm_dp_mst_port *port = intel_connector->port;
> +	int ret = 0;
>  
>  	old_conn_state = drm_atomic_get_old_connector_state(state, connector);
>  	old_crtc = old_conn_state->crtc;
>  	if (!old_crtc)
>  		return ret;
>  
> -	crtc_state = drm_atomic_get_new_crtc_state(state, old_crtc);
> -	slots = to_intel_crtc_state(crtc_state)->dp_m_n.tu;
> -	if (drm_atomic_crtc_needs_modeset(crtc_state) && slots > 0) {
> -		struct drm_dp_mst_topology_mgr *mgr;
> -		struct drm_encoder *old_encoder;
> +	/* Free VCPI, since compute_config() won't be run */
> +	if (!new_conn_state->crtc) {
> +		crtc_state = drm_atomic_get_new_crtc_state(state, old_crtc);
>  
> -		old_encoder = old_conn_state->best_encoder;
> -		mgr = &enc_to_mst(old_encoder)->primary->dp.mst_mgr;
> -
> -		ret = drm_dp_atomic_release_vcpi_slots(state, mgr, slots);
> -		if (ret)
> -			DRM_DEBUG_KMS("failed releasing %d vcpi slots:%d\n", slots,
ret);
> -		else
> -			to_intel_crtc_state(crtc_state)->dp_m_n.tu = 0;
> +		ret = drm_dp_atomic_release_vcpi_slots(state, mgr, port);
> +		if (ret) {
> +			DRM_DEBUG_KMS("failed releasing vcpi slots: %d\n",
> +				      ret);
> +			return ret;
> +		}
> +		to_intel_crtc_state(crtc_state)->dp_m_n.tu = 0;
>  	}
> +
>  	return ret;
>  }
>  
> diff --git a/include/drm/drm_dp_mst_helper.h
b/include/drm/drm_dp_mst_helper.h
> index 3faceb66f5cb..08b67948b8f9 100644
> --- a/include/drm/drm_dp_mst_helper.h
> +++ b/include/drm/drm_dp_mst_helper.h
> @@ -406,9 +406,15 @@ struct drm_dp_payload {
>  
>  #define to_dp_mst_topology_state(x) container_of(x, struct
drm_dp_mst_topology_state, base)
>  
> +struct drm_dp_vcpi_allocation {
> +	struct drm_dp_mst_port *port;
> +	int vcpi;
> +	struct list_head next;
> +};
> +
>  struct drm_dp_mst_topology_state {
>  	struct drm_private_state base;
> -	int avail_slots;
> +	struct list_head vcpis;
>  	struct drm_dp_mst_topology_mgr *mgr;
>  };
>  
> @@ -619,14 +625,17 @@ void drm_dp_mst_topology_mgr_suspend(struct
drm_dp_mst_topology_mgr *mgr);
>  int drm_dp_mst_topology_mgr_resume(struct drm_dp_mst_topology_mgr *mgr);
>  struct drm_dp_mst_topology_state *drm_atomic_get_mst_topology_state(struct
drm_atomic_state *state,
>  								    struct drm_dp_mst_topology_mgr *mgr);
> -int drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
> -				  struct drm_dp_mst_topology_mgr *mgr,
> -				  struct drm_dp_mst_port *port, int pbn);
> -int drm_dp_atomic_release_vcpi_slots(struct drm_atomic_state *state,
> -				     struct drm_dp_mst_topology_mgr *mgr,
> -				     int slots);
> +int __must_check
> +drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
> +			      struct drm_dp_mst_topology_mgr *mgr,
> +			      struct drm_dp_mst_port *port, int pbn);
> +int __must_check
> +drm_dp_atomic_release_vcpi_slots(struct drm_atomic_state *state,
> +				 struct drm_dp_mst_topology_mgr *mgr,
> +				 struct drm_dp_mst_port *port);
>  int drm_dp_send_power_updown_phy(struct drm_dp_mst_topology_mgr *mgr,
>  				 struct drm_dp_mst_port *port, bool power_up);
> +int __must_check drm_dp_mst_atomic_check(struct drm_atomic_state *state);
>  
>  extern const struct drm_private_state_funcs
drm_dp_mst_topology_state_funcs;
>  
> -- 
> 2.19.1
> 
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch