Nouveau - Nov 2018 - [PATCH v6 3/6] drm/dp_mst: Start tracking per-port VCPI allocations

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.

[sorry for still not adding your R-Bs! I ended up needing to make a
lot of changes to make it so we do actually kref() each port in the
atomic state]
Cc: Daniel Vetter <daniel at ffwll.ch>

Lyude Paul (6):
  drm/dp_mst: Add some atomic state iterator macros
  drm/dp_mst: Return kref_put() result from drm_dp_put_port()
  drm/dp_mst: Start tracking per-port VCPI allocations
  drm/dp_mst: Check payload count in drm_dp_mst_atomic_check()
  drm/nouveau: Stop unsetting mstc->port, check connector registration
  drm/nouveau: Use atomic VCPI helpers for MST

 drivers/gpu/drm/drm_dp_mst_topology.c   | 307 +++++++++++++++++++++---
 drivers/gpu/drm/i915/intel_display.c    |   4 +
 drivers/gpu/drm/i915/intel_dp_mst.c     |  64 +++--
 drivers/gpu/drm/nouveau/dispnv50/disp.c |  67 ++++--
 include/drm/drm_dp_mst_helper.h         | 101 +++++++-
 5 files changed, 459 insertions(+), 84 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

This will let us warn if we end up freeing a port when we're not
expecting to, which will make reporting erroneous usage of the new MST
VCPI helpers a little easier.

Signed-off-by: Lyude Paul <lyude at redhat.com>
Cc: Daniel Vetter <daniel at ffwll.ch>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
b/drivers/gpu/drm/drm_dp_mst_topology.c
index 529414556962..00fbe7a2699d 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -45,7 +45,7 @@ static bool dump_dp_payload_table(struct
drm_dp_mst_topology_mgr *mgr,
 				  char *buf);
 static int test_calc_pbn_mode(void);
 
-static void drm_dp_put_port(struct drm_dp_mst_port *port);
+static int drm_dp_put_port(struct drm_dp_mst_port *port);
 
 static int drm_dp_dpcd_write_payload(struct drm_dp_mst_topology_mgr *mgr,
 				     int id,
@@ -969,9 +969,9 @@ static void drm_dp_destroy_port(struct kref *kref)
 	kfree(port);
 }
 
-static void drm_dp_put_port(struct drm_dp_mst_port *port)
+static int drm_dp_put_port(struct drm_dp_mst_port *port)
 {
-	kref_put(&port->kref, drm_dp_destroy_port);
+	return kref_put(&port->kref, drm_dp_destroy_port);
 }
 
 static struct drm_dp_mst_branch
*drm_dp_mst_get_validated_mstb_ref_locked(struct drm_dp_mst_branch *mstb, struct
drm_dp_mst_branch *to_find)
-- 
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 v6:
 - Keep a kref to all of the ports we have allocations on. This required
   a good bit of changing to when we call drm_dp_find_vcpi_slots(),
   mainly that we need to ensure that we only redo VCPI allocations on
   actual mode or CRTC changes, not crtc_state->active changes.
   Additionally, we no longer take the registration of the DRM connector
   for each port into account because so long as we have a kref to the
   port in the new or previous atomic state, the connector will stay
   registered.
 - Use the small changes to drm_dp_put_port() to add even more error
   checking to make misusage of the helpers more obvious. I added this
   after having to chase down various use-after-free conditions that
   started popping up from the new helpers so no one else has to
   troubleshoot that.
 - Move some accidental DRM_DEBUG_KMS() calls to DRM_DEBUG_ATOMIC()
 - Update documentation again, note that find/release() should both not be
   called on the same port in a single atomic check phase (but multiple
   calls to one or the other is OK)

Changes since v4:
 - Don't skip the atomic checks for VCPI allocations if no new VCPI
   allocations happen in a state. This makes the next change I'm about
   to list here a lot easier to implement.
 - Don't ignore VCPI allocations on destroyed ports, instead ensure that
   when ports are destroyed and still have VCPI allocations in the
   topology state, the only state changes allowed are releasing said
   ports' VCPI. This prevents a state with a mix of VCPI allocations
   from destroyed ports, and allocations from valid ports.

Changes since v3:
 - Don't release VCPI allocations in the topology state immediately in
   drm_dp_atomic_release_vcpi_slots(), instead mark them as 0 and skip
   over them in drm_dp_mst_duplicate_state(). This makes it so
   drm_dp_atomic_release_vcpi_slots() is still idempotent while also
   throwing warnings if the driver messes up it's book keeping and tries
   to release VCPI slots on a port that doesn't have any pre-existing
   VCPI allocation - danvet
 - Change mst_state/state in some debugging messages to "mst state"

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 | 294 +++++++++++++++++++++++---
 drivers/gpu/drm/i915/intel_display.c  |   4 +
 drivers/gpu/drm/i915/intel_dp_mst.c   |  64 +++---
 include/drm/drm_dp_mst_helper.h       |  24 ++-
 4 files changed, 319 insertions(+), 67 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
b/drivers/gpu/drm/drm_dp_mst_topology.c
index 00fbe7a2699d..183d0e832ced 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2617,21 +2617,42 @@ 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, but only when
+ * &drm_crtc_state.mode_changed or &drm_crtc_state.connectors_changed
is set
+ * to ensure compatibility with userspace applications that still use the
+ * legacy modesetting UAPI.
+ *
+ * Allocations set by this function are not checked against the bandwidth
+ * restraints of @mgr until the driver calls drm_dp_mst_atomic_check().
+ *
+ * Additionally, it is OK to call this function multiple times on the same
+ * @port as needed. It is not OK however, to call this function and
+ * drm_dp_atomic_release_vcpi_slots() in the same atomic check phase.
+ *
+ * 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))
@@ -2640,20 +2661,60 @@ 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;
+	topology_state->vcpi_allocated = true;
+
+	/* 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;
+
+			/*
+			 * This should never happen, unless the driver tries
+			 * releasing and allocating the same VCPI allocation,
+			 * which is an error
+			 */
+			if (WARN_ON(!prev_slots)) {
+				DRM_ERROR("cannot allocate and release VCPI on [MST PORT:%p] in the
same state\n",
+					  port);
+				return -EINVAL;
+			}
+
+			break;
+		}
 	}
+	if (!vcpi)
+		prev_slots = 0;
 
-	topology_state->avail_slots -= req_slots;
-	DRM_DEBUG_KMS("vcpi slots avail=%d",
topology_state->avail_slots);
+	req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
+
+	DRM_DEBUG_ATOMIC("[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 = drm_dp_get_validated_port_ref(mgr, port);
+		if (!vcpi->port) {
+			ret = -EINVAL;
+			kfree(vcpi);
+			goto out;
+		}
+		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);
 
@@ -2661,31 +2722,66 @@ 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) when it had VCPI allocated in the previous atomic state.
+ *
+ * It is OK to call this even if @port has been removed from the system.
+ * Additionally, it is OK to call this function multiple times on the same
+ * @port as needed. It is not OK however, to call this function and
+ * drm_dp_atomic_find_vcpi_slots() on the same @port in a single atomic check
+ * phase.
+ *
+ * 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 *pos;
+	bool found = false;
 
 	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(pos, &topology_state->vcpis, next) {
+		if (pos->port == port) {
+			found = true;
+			break;
+		}
+	}
+	if (WARN_ON(!found)) {
+		DRM_ERROR("no VCPI for [MST PORT:%p] found in mst state %p\n",
+			  port, &topology_state->base);
+		return -EINVAL;
+	}
+
+	DRM_DEBUG_ATOMIC("[MST PORT:%p] VCPI %d -> 0\n", port,
pos->vcpi);
+	if (pos->vcpi) {
+		/*
+		 * This should be safe-as the previous state will still hold a
+		 * reference to this port until we swap states. If it's not,
+		 * the driver has a bookkeeping error
+		 */
+		if (WARN_ON(drm_dp_put_port(port))) {
+			DRM_ERROR("cannot allocate and release VCPI on [MST PORT:%p] in the
same state\n",
+				  port);
+			return -EINVAL;
+		}
+		pos->vcpi = 0;
+	}
 
 	return 0;
 }
@@ -3115,15 +3211,45 @@ 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);
+	state->vcpi_allocated = false;
+
+	list_for_each_entry(pos, &old_state->vcpis, next) {
+		/* Prune leftover freed VCPI allocations */
+		if (!pos->vcpi)
+			continue;
+
+		vcpi = kmemdup(pos, sizeof(*vcpi), GFP_KERNEL);
+		if (!vcpi)
+			goto fail;
+
+		/* Take a plain old kref here and don't validate the port, as
+		 * it's topology might not even exist anymore
+		 */
+		kref_get(&vcpi->port->kref);
+		list_add(&vcpi->next, &state->vcpis);
+	}
+
 	return &state->base;
+
+fail:
+	list_for_each_entry_safe(pos, vcpi, &state->vcpis, next) {
+		drm_dp_put_port(pos->port);
+		kfree(pos);
+	}
+	kfree(state);
+
+	return NULL;
 }
 
 static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
@@ -3131,14 +3257,116 @@ 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) {
+		/* We only keep references to ports with non-zero VCPIs */
+		if (pos->vcpi)
+			drm_dp_put_port(pos->port);
+		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;
+
+	/* There's no possible scenario where releasing VCPI or keeping it the
+	 * same would make the state invalid
+	 */
+	if (!mst_state->vcpi_allocated) {
+		DRM_DEBUG_ATOMIC("[MST MGR:%p] state %p allocates no VCPI, check
skipped\n",
+				 mgr, &mst_state->base);
+		return 0;
+	}
+
+	list_for_each_entry(vcpi, &mst_state->vcpis, next) {
+		/* Releasing VCPI is always OK-even if the port is gone */
+		if (!vcpi->vcpi) {
+			DRM_DEBUG_ATOMIC("[MST PORT:%p] releases all VCPI slots\n",
+					 vcpi->port);
+			continue;
+		}
+
+		port = drm_dp_get_validated_port_ref(mgr, vcpi->port);
+		if (!port) {
+			DRM_DEBUG_ATOMIC("[MST PORT:%p] is gone but still has VCPI, cannot add
new VCPI\n",
+					 vcpi->port);
+			return -EINVAL;
+		}
+
+		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
@@ -3216,13 +3444,11 @@ 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 132e978227fb..8e85e04a5948 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -12592,6 +12592,10 @@ 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 4de247ddf05f..be2d1ac7d87d 100644
--- a/drivers/gpu/drm/i915/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/intel_dp_mst.c
@@ -41,8 +41,13 @@ static bool intel_dp_mst_compute_config(struct intel_encoder
*encoder,
 	struct drm_connector *connector = conn_state->connector;
 	void *port = to_intel_connector(connector)->port;
 	struct drm_atomic_state *state = pipe_config->base.state;
+	struct drm_crtc *crtc = pipe_config->base.crtc;
+	struct drm_crtc_state *old_crtc_state +		drm_atomic_get_old_crtc_state(state,
crtc);
+	struct drm_crtc_state *new_crtc_state = &pipe_config->base;
 	int bpp;
-	int lane_count, slots = 0;
+	int lane_count, slots +		to_intel_crtc_state(old_crtc_state)->dp_m_n.tu;
 	const struct drm_display_mode *adjusted_mode =
&pipe_config->base.adjusted_mode;
 	int mst_pbn;
 	bool constant_n = drm_dp_has_quirk(&intel_dp->desc,
@@ -77,8 +82,12 @@ static bool intel_dp_mst_compute_config(struct intel_encoder
*encoder,
 	mst_pbn = drm_dp_calc_pbn_mode(adjusted_mode->crtc_clock, bpp);
 	pipe_config->pbn = mst_pbn;
 
-	/* Zombie connectors can't have VCPI slots */
-	if (!drm_connector_is_unregistered(connector)) {
+	/* Only change VCPI allocation on actual mode changes, to prevent us
+	 * from trying to allocate VCPI to ports that no longer exist when we
+	 * may just be trying to disable DPMS on them
+	 */
+	if (new_crtc_state->mode_changed ||
+	    new_crtc_state->connectors_changed) {
 		slots = drm_dp_atomic_find_vcpi_slots(state,
 						      &intel_dp->mst_mgr,
 						      port,
@@ -107,36 +116,39 @@ static bool intel_dp_mst_compute_config(struct
intel_encoder *encoder,
 	return true;
 }
 
-static int intel_dp_mst_atomic_check(struct drm_connector *connector,
-		struct drm_connector_state *new_conn_state)
+static int
+intel_dp_mst_atomic_check(struct drm_connector *connector,
+			  struct drm_connector_state *new_conn_state)
 {
+	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;
 	struct drm_atomic_state *state = new_conn_state->state;
-	struct drm_connector_state *old_conn_state;
-	struct drm_crtc *old_crtc;
-	struct drm_crtc_state *crtc_state;
-	int slots, ret = 0;
+	struct drm_connector_state *old_conn_state +	
drm_atomic_get_old_connector_state(state, connector);
+	struct drm_crtc *old_crtc = old_conn_state->crtc,
+			*new_crtc = new_conn_state->crtc;
+	struct drm_crtc_state *old_crtc_state, *new_crtc_state;
 
-	old_conn_state = drm_atomic_get_old_connector_state(state, connector);
-	old_crtc = old_conn_state->crtc;
 	if (!old_crtc)
-		return ret;
+		return 0;
 
-	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;
+	old_crtc_state = drm_atomic_get_old_crtc_state(state, old_crtc);
+	if (!old_crtc_state ||
+	    !to_intel_crtc_state(old_crtc_state)->dp_m_n.tu)
+		return 0;
 
-		old_encoder = old_conn_state->best_encoder;
-		mgr = &enc_to_mst(old_encoder)->primary->dp.mst_mgr;
+	/* If we switched CRTCs, clear the previous one's allocation */
+	new_crtc_state = drm_atomic_get_new_crtc_state(state, old_crtc);
+	if (new_crtc_state->connectors_changed &&
!new_crtc_state->enable)
+		to_intel_crtc_state(new_crtc_state)->dp_m_n.tu = 0;
 
-		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;
-	}
-	return ret;
+	if (new_crtc)
+		return 0;
+
+	return drm_dp_atomic_release_vcpi_slots(state, mgr, port);
 }
 
 static void intel_mst_disable_dp(struct intel_encoder *encoder,
diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
index 3faceb66f5cb..2392e12b6bce 100644
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -406,9 +406,16 @@ 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;
+	u8 vcpi_allocated;
 	struct drm_dp_mst_topology_mgr *mgr;
 };
 
@@ -619,14 +626,17 @@ 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 183d0e832ced..38654a449b82 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -3275,7 +3275,7 @@ 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;
 
 	/* There's no possible scenario where releasing VCPI or keeping it the
 	 * same would make the state invalid
@@ -3313,6 +3313,13 @@ 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

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 6cbbae3f438b..f216fd4207c9 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;
@@ -822,7 +825,7 @@ 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);
@@ -935,7 +938,7 @@ 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);
@@ -1073,10 +1076,6 @@ 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

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.

Changes since v5:
 - Update nv50_msto_atomic_check() and nv50_mstc_atomic_check() to the
   new requirements for drm_dp_atomic_find_vcpi_slots() and
   drm_dp_atomic_release_vcpi_slots()

Signed-off-by: Lyude Paul <lyude at redhat.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 drivers/gpu/drm/nouveau/dispnv50/disp.c | 52 ++++++++++++++++++++++---
 1 file changed, 46 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c
b/drivers/gpu/drm/nouveau/dispnv50/disp.c
index f216fd4207c9..83cb1afb94ed 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -750,16 +750,22 @@ 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);
+	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;
+	if (crtc_state->connectors_changed || crtc_state->mode_changed) {
+		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);
@@ -923,12 +929,42 @@ 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 +	
drm_atomic_get_old_connector_state(state, connector);
+	struct drm_crtc_state *old_crtc_state;
+	struct drm_crtc *new_crtc = new_conn_state->crtc,
+			*old_crtc = old_conn_state->crtc;
+
+	if (!old_crtc)
+		return 0;
+
+	old_crtc_state = drm_atomic_get_old_crtc_state(state, old_crtc);
+	if (!old_crtc_state || !old_crtc_state->enable)
+		return 0;
+
+	if (new_crtc)
+		return 0;
+
+	/* This connector will be left without an enabled CRTC, so its VCPI
+	 * must be released here
+	 */
+	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
@@ -2108,6 +2144,10 @@ 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

On Thu, Nov 15, 2018 at 07:50:03PM -0500, Lyude Paul
wrote:
> 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)
Just noticed that this patch is missing the EXPORT_SYMBOL, which is
burried in patch 3. Needs to be moved. A tiny bit of kerneldoc along the
lines of "never use this directly" would be good too :-)
-Daniel
> +		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
> 
> _______________________________________________
> Nouveau mailing list
> Nouveau at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/nouveau
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

On Thu, Nov 15, 2018 at 07:50:05PM -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 v6:
>  - Keep a kref to all of the ports we have allocations on. This required
>    a good bit of changing to when we call drm_dp_find_vcpi_slots(),
>    mainly that we need to ensure that we only redo VCPI allocations on
>    actual mode or CRTC changes, not crtc_state->active changes.
>    Additionally, we no longer take the registration of the DRM connector
>    for each port into account because so long as we have a kref to the
>    port in the new or previous atomic state, the connector will stay
>    registered.
I write an entire pile of small nitpits (still included most of them
below), until I realized this here wont work. Delaying the call to destroy
the connector (well, unregister it really) wreaks the design we've come up
with thus far, resulting in most of my comments here.

Instead, all we need to do is delay the kfree(port) at the bottom of
drm_dp_destroy_port(). The vcpi allocation structure _only_ needs the
pointer value to stay valid, as a lookup key. It doesn't care at all about
anything actually stored in there. So the only thing we need to delay is
the kfree. I think the simplest way to achieve this is to add a 2nd kref
(port->kfree_ref or something like that), with on reference held by the
port itself (released in drm_dp_destroy_port), and the other one held
as-needed by the vcpi allocation lists.

I think if we go with this design instead of retrofitting a semantic
change of the port lifetime itself, all the complications I complain about
below should disappear.

Piles of comments below.

Cheers, Daniel
>  - Use the small changes to drm_dp_put_port() to add even more error
>    checking to make misusage of the helpers more obvious. I added this
>    after having to chase down various use-after-free conditions that
>    started popping up from the new helpers so no one else has to
>    troubleshoot that.
>  - Move some accidental DRM_DEBUG_KMS() calls to DRM_DEBUG_ATOMIC()
>  - Update documentation again, note that find/release() should both not be
>    called on the same port in a single atomic check phase (but multiple
>    calls to one or the other is OK)
> 
> Changes since v4:
>  - Don't skip the atomic checks for VCPI allocations if no new VCPI
>    allocations happen in a state. This makes the next change I'm about
>    to list here a lot easier to implement.
>  - Don't ignore VCPI allocations on destroyed ports, instead ensure
that
>    when ports are destroyed and still have VCPI allocations in the
>    topology state, the only state changes allowed are releasing said
>    ports' VCPI. This prevents a state with a mix of VCPI allocations
>    from destroyed ports, and allocations from valid ports.
> 
> Changes since v3:
>  - Don't release VCPI allocations in the topology state immediately in
>    drm_dp_atomic_release_vcpi_slots(), instead mark them as 0 and skip
>    over them in drm_dp_mst_duplicate_state(). This makes it so
>    drm_dp_atomic_release_vcpi_slots() is still idempotent while also
>    throwing warnings if the driver messes up it's book keeping and
tries
>    to release VCPI slots on a port that doesn't have any pre-existing
>    VCPI allocation - danvet
>  - Change mst_state/state in some debugging messages to "mst
state"
> 
> 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 | 294 +++++++++++++++++++++++---
>  drivers/gpu/drm/i915/intel_display.c  |   4 +
>  drivers/gpu/drm/i915/intel_dp_mst.c   |  64 +++---
>  include/drm/drm_dp_mst_helper.h       |  24 ++-
>  4 files changed, 319 insertions(+), 67 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 00fbe7a2699d..183d0e832ced 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -2617,21 +2617,42 @@ 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, but only when
> + * &drm_crtc_state.mode_changed or
&drm_crtc_state.connectors_changed is set
> + * to ensure compatibility with userspace applications that still use the
> + * legacy modesetting UAPI.
> + *
> + * Allocations set by this function are not checked against the bandwidth
> + * restraints of @mgr until the driver calls drm_dp_mst_atomic_check().
> + *
> + * Additionally, it is OK to call this function multiple times on the same
> + * @port as needed. It is not OK however, to call this function and
> + * drm_dp_atomic_release_vcpi_slots() in the same atomic check phase.
> + *
> + * 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))
> @@ -2640,20 +2661,60 @@ 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;
> +	topology_state->vcpi_allocated = true;
> +
> +	/* 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;
> +
> +			/*
> +			 * This should never happen, unless the driver tries
> +			 * releasing and allocating the same VCPI allocation,
> +			 * which is an error
> +			 */
> +			if (WARN_ON(!prev_slots)) {
> +				DRM_ERROR("cannot allocate and release VCPI on [MST PORT:%p] in
the same state\n",
> +					  port);
> +				return -EINVAL;
> +			}
Allowing atomic changes to output state (like disabling it on one crtc,
and then enabling on the other, thus both releasing and re-allocating the
vcpi in one go) is kinda the point of atomic. So definitely can't EINVAL
here.

Sounds like we need more testcases in igt?
> +
> +			break;
> +		}
>  	}
> +	if (!vcpi)
> +		prev_slots = 0;
>  
> -	topology_state->avail_slots -= req_slots;
> -	DRM_DEBUG_KMS("vcpi slots avail=%d",
topology_state->avail_slots);
> +	req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
> +
> +	DRM_DEBUG_ATOMIC("[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 = drm_dp_get_validated_port_ref(mgr, port);
> +		if (!vcpi->port) {
> +			ret = -EINVAL;
> +			kfree(vcpi);
> +			goto out;
> +		}
> +		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);
>  
> @@ -2661,31 +2722,66 @@ 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) when it had VCPI allocated in the previous atomic state.
> + *
> + * It is OK to call this even if @port has been removed from the system.
> + * Additionally, it is OK to call this function multiple times on the same
> + * @port as needed. It is not OK however, to call this function and
> + * drm_dp_atomic_find_vcpi_slots() on the same @port in a single atomic
check
> + * phase.
> + *
> + * 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 *pos;
> +	bool found = false;
>  
>  	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(pos, &topology_state->vcpis, next) {
> +		if (pos->port == port) {
> +			found = true;
> +			break;
> +		}
> +	}
> +	if (WARN_ON(!found)) {
> +		DRM_ERROR("no VCPI for [MST PORT:%p] found in mst state %p\n",
> +			  port, &topology_state->base);
> +		return -EINVAL;
> +	}
> +
> +	DRM_DEBUG_ATOMIC("[MST PORT:%p] VCPI %d -> 0\n", port,
pos->vcpi);
> +	if (pos->vcpi) {
> +		/*
> +		 * This should be safe-as the previous state will still hold a
> +		 * reference to this port until we swap states. If it's not,
> +		 * the driver has a bookkeeping error
> +		 */
> +		if (WARN_ON(drm_dp_put_port(port))) {
The usual way to do this (instead of adding a return value to the normal
_put function) is something like

	kref_put(port, function_that_with_just_a_WARNING_DRM_ERROR)

avoids the need for patch 2.
> +			DRM_ERROR("cannot allocate and release VCPI on [MST PORT:%p] in
the same state\n",
> +				  port);
> +			return -EINVAL;
> +		}
> +		pos->vcpi = 0;
> +	}
>  
>  	return 0;
>  }
> @@ -3115,15 +3211,45 @@ 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);
> +	state->vcpi_allocated = false;
> +
> +	list_for_each_entry(pos, &old_state->vcpis, next) {
> +		/* Prune leftover freed VCPI allocations */
> +		if (!pos->vcpi)
> +			continue;
> +
> +		vcpi = kmemdup(pos, sizeof(*vcpi), GFP_KERNEL);
> +		if (!vcpi)
> +			goto fail;
> +
> +		/* Take a plain old kref here and don't validate the port, as
> +		 * it's topology might not even exist anymore
> +		 */
> +		kref_get(&vcpi->port->kref);
> +		list_add(&vcpi->next, &state->vcpis);
> +	}
> +
>  	return &state->base;
> +
> +fail:
> +	list_for_each_entry_safe(pos, vcpi, &state->vcpis, next) {
> +		drm_dp_put_port(pos->port);
> +		kfree(pos);
> +	}
> +	kfree(state);
> +
> +	return NULL;
>  }
>  
>  static void drm_dp_mst_destroy_state(struct drm_private_obj *obj,
> @@ -3131,14 +3257,116 @@ 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) {
> +		/* We only keep references to ports with non-zero VCPIs */
> +		if (pos->vcpi)
> +			drm_dp_put_port(pos->port);
> +		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;
> +
> +	/* There's no possible scenario where releasing VCPI or keeping it
the
> +	 * same would make the state invalid
> +	 */
> +	if (!mst_state->vcpi_allocated) {
Do we need this? If not I'm always in favour of removing code if it's
not
needed :-)
> +		DRM_DEBUG_ATOMIC("[MST MGR:%p] state %p allocates no VCPI, check
skipped\n",
> +				 mgr, &mst_state->base);
> +		return 0;
> +	}
> +
> +	list_for_each_entry(vcpi, &mst_state->vcpis, next) {
> +		/* Releasing VCPI is always OK-even if the port is gone */
> +		if (!vcpi->vcpi) {
> +			DRM_DEBUG_ATOMIC("[MST PORT:%p] releases all VCPI slots\n",
> +					 vcpi->port);
> +			continue;
> +		}
> +
> +		port = drm_dp_get_validated_port_ref(mgr, vcpi->port);
> +		if (!port) {
> +			DRM_DEBUG_ATOMIC("[MST PORT:%p] is gone but still has VCPI, cannot
add new VCPI\n",
> +					 vcpi->port);
> +			return -EINVAL;
> +		}
For find_vcpi we've already done this. For unplugged vcpi, we can't do
this here I think - otherwise if you enable 2 mst outputs on the same
branch, and unplug both, old non-atomic userspace can never ever again
disable them because it can't disable both. The check (to skip already
deallocated ports) above isn't enough to handle that.
> +
> +		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
> @@ -3216,13 +3444,11 @@ 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 132e978227fb..8e85e04a5948 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -12592,6 +12592,10 @@ 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 4de247ddf05f..be2d1ac7d87d 100644
> --- a/drivers/gpu/drm/i915/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/intel_dp_mst.c
> @@ -41,8 +41,13 @@ static bool intel_dp_mst_compute_config(struct
intel_encoder *encoder,
>  	struct drm_connector *connector = conn_state->connector;
>  	void *port = to_intel_connector(connector)->port;
>  	struct drm_atomic_state *state = pipe_config->base.state;
> +	struct drm_crtc *crtc = pipe_config->base.crtc;
> +	struct drm_crtc_state *old_crtc_state > +	
drm_atomic_get_old_crtc_state(state, crtc);
> +	struct drm_crtc_state *new_crtc_state = &pipe_config->base;
>  	int bpp;
> -	int lane_count, slots = 0;
> +	int lane_count, slots > +	
to_intel_crtc_state(old_crtc_state)->dp_m_n.tu;
>  	const struct drm_display_mode *adjusted_mode =
&pipe_config->base.adjusted_mode;
>  	int mst_pbn;
>  	bool constant_n = drm_dp_has_quirk(&intel_dp->desc,
> @@ -77,8 +82,12 @@ static bool intel_dp_mst_compute_config(struct
intel_encoder *encoder,
>  	mst_pbn = drm_dp_calc_pbn_mode(adjusted_mode->crtc_clock, bpp);
>  	pipe_config->pbn = mst_pbn;
>  
> -	/* Zombie connectors can't have VCPI slots */
> -	if (!drm_connector_is_unregistered(connector)) {
> +	/* Only change VCPI allocation on actual mode changes, to prevent us
> +	 * from trying to allocate VCPI to ports that no longer exist when we
> +	 * may just be trying to disable DPMS on them
> +	 */
> +	if (new_crtc_state->mode_changed ||
> +	    new_crtc_state->connectors_changed) {
Why exactly is this needed? We only call compute_config on the enocoder
when enabling an output. Not when disabling one. Similar for the atomic
helpers and the various encoder callbacks (you have the same change in the
nouveau code). Did this actually blow up while testing?
>  		slots = drm_dp_atomic_find_vcpi_slots(state,
>  						      &intel_dp->mst_mgr,
>  						      port,
> @@ -107,36 +116,39 @@ static bool intel_dp_mst_compute_config(struct
intel_encoder *encoder,
>  	return true;
>  }
>  
> -static int intel_dp_mst_atomic_check(struct drm_connector *connector,
> -		struct drm_connector_state *new_conn_state)
> +static int
> +intel_dp_mst_atomic_check(struct drm_connector *connector,
> +			  struct drm_connector_state *new_conn_state)
>  {
> +	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;
>  	struct drm_atomic_state *state = new_conn_state->state;
> -	struct drm_connector_state *old_conn_state;
> -	struct drm_crtc *old_crtc;
> -	struct drm_crtc_state *crtc_state;
> -	int slots, ret = 0;
> +	struct drm_connector_state *old_conn_state > +	
drm_atomic_get_old_connector_state(state, connector);
> +	struct drm_crtc *old_crtc = old_conn_state->crtc,
> +			*new_crtc = new_conn_state->crtc;
> +	struct drm_crtc_state *old_crtc_state, *new_crtc_state;
>  
> -	old_conn_state = drm_atomic_get_old_connector_state(state, connector);
> -	old_crtc = old_conn_state->crtc;
Bikeshed: Reworking all the above hides the real changes quite a bit.
>  	if (!old_crtc)
> -		return ret;
> +		return 0;
>  
> -	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;
> +	old_crtc_state = drm_atomic_get_old_crtc_state(state, old_crtc);
> +	if (!old_crtc_state ||
!old_crtc_state would be a framework bug. Just remove that check.
> +	    !to_intel_crtc_state(old_crtc_state)->dp_m_n.tu)
> +		return 0;
Hm, why do we need this? Having a DP port previously enabled with a 0 tu
sounds like a pretty big driver bug.
>  
> -		old_encoder = old_conn_state->best_encoder;
> -		mgr = &enc_to_mst(old_encoder)->primary->dp.mst_mgr;
> +	/* If we switched CRTCs, clear the previous one's allocation */
> +	new_crtc_state = drm_atomic_get_new_crtc_state(state, old_crtc);
> +	if (new_crtc_state->connectors_changed &&
!new_crtc_state->enable)
> +		to_intel_crtc_state(new_crtc_state)->dp_m_n.tu = 0;
No idea why we need to clear this here? Shouldn't we just clear this
unconditionally if we release the allocation.

Also naming convention, I'd call this old_crtc_new_state, and maybe
old_crtc_old_state. To make it clear these are the old/new states for
old_crtc. Instead of old/new state for the new crtc.
>  
> -		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;
> -	}
> -	return ret;
> +	if (new_crtc)
> +		return 0;
Not sure why we shouldn't release this? If we handle this in helpers, it
would remove piles of special casing code here I think. Plus remove
special code in the hlpers.

> +
> +	return drm_dp_atomic_release_vcpi_slots(state, mgr, port);
>  }
>  
>  static void intel_mst_disable_dp(struct intel_encoder *encoder,
> diff --git a/include/drm/drm_dp_mst_helper.h
b/include/drm/drm_dp_mst_helper.h
> index 3faceb66f5cb..2392e12b6bce 100644
> --- a/include/drm/drm_dp_mst_helper.h
> +++ b/include/drm/drm_dp_mst_helper.h
> @@ -406,9 +406,16 @@ 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 {
I think a comment here that this pointer holds a full reference (even past
when the connector is unplugged) would be good. Otherwise the loop in
release_vcpi would be buggy.
> +	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;
> +	u8 vcpi_allocated;
>  	struct drm_dp_mst_topology_mgr *mgr;
>  };
>  
> @@ -619,14 +626,17 @@ 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