[IM] Update GetMinSubscriptionsPerFabric (#20207)

src/app/InteractionModelEngine.cpp

@@ -28,6 +28,7 @@
 #include <cinttypes>
 
 #include <lib/core/CHIPTLVUtilities.hpp>
+#include <lib/support/CodeUtils.h>
 
 extern bool emberAfContainsAttribute(chip::EndpointId endpoint, chip::ClusterId clusterId, chip::AttributeId attributeId);
 
@@ -1370,19 +1371,14 @@ bool InteractionModelEngine::HasActiveRead()
  }) == Loop::Break));
 }
 
-uint16_t InteractionModelEngine::GetMinSubscriptionsPerFabric() const
+uint16_t InteractionModelEngine::GetMinGuaranteedSubscriptionsPerFabric() const
 {
- uint8_t fabricCount = mpFabricTable->FabricCount();
- const size_t readHandlerPoolCapacity = GetReadHandlerPoolCapacityForSubscriptions();
-
- if (fabricCount == 0)
- {
- return kMinSupportedSubscriptionsPerFabric;
- }
-
- size_t perFabricSubscriptionCapacity = readHandlerPoolCapacity / fabricCount;
-
- return static_cast<uint16_t>(perFabricSubscriptionCapacity);
+#if CHIP_SYSTEM_CONFIG_POOL_USE_HEAP
+ return UINT16_MAX;
+#else
+ return static_cast<uint16_t>(
+ min(GetReadHandlerPoolCapacityForSubscriptions() / GetConfigMaxFabrics(), static_cast<size_t>(UINT16_MAX)));
+#endif
 }
 
 size_t InteractionModelEngine::GetNumDirtySubscriptions() const

src/app/InteractionModelEngine.h

@@ -87,8 +87,8 @@ class InteractionModelEngine : public Messaging::UnsolicitedMessageHandler,
  * Spec 8.5.1 A publisher SHALL always ensure that every fabric the node is commissioned into can create at least three
  * subscriptions to the publisher and that each subscription SHALL support at least 3 attribute/event paths.
  */
- static constexpr size_t kMinSupportedSubscriptionsPerFabric = 2;
- static constexpr size_t kMinSupportedPathsPerSubscription = 2;
+ static constexpr size_t kMinSupportedSubscriptionsPerFabric = 3;
+ static constexpr size_t kMinSupportedPathsPerSubscription = 3;
  static constexpr size_t kMinSupportedPathsPerReadRequest = 9;
  static constexpr size_t kMinSupportedReadRequestsPerFabric = 1;
  static constexpr size_t kReadHandlerPoolSize = CHIP_IM_MAX_NUM_SUBSCRIPTIONS + CHIP_IM_MAX_NUM_READS;
@@ -260,7 +260,13 @@ class InteractionModelEngine : public Messaging::UnsolicitedMessageHandler,
  */
  bool TrimFabricForRead(FabricIndex aFabricIndex);
 
- uint16_t GetMinSubscriptionsPerFabric() const;
+ /**
+ * Returns the minimal value of guaranteed subscriptions per fabic. UINT16_MAX will be returned if current app is configured to
+ * use heap for the object pools used by interaction model engine.
+ *
+ * @retval the minimal value of guaranteed subscriptions per fabic.
+ */
+ uint16_t GetMinGuaranteedSubscriptionsPerFabric() const;
 
 #if CONFIG_BUILD_FOR_HOST_UNIT_TEST
  //

src/app/clusters/basic/basic.cpp

@@ -275,7 +275,7 @@ CHIP_ERROR BasicAttrAccess::Read(const ConcreteReadAttributePath & aPath, Attrib
  constexpr uint16_t kMinCaseSessionsPerFabricMandatedBySpec = 3;
 
  capabilityMinima.caseSessionsPerFabric = kMinCaseSessionsPerFabricMandatedBySpec;
- capabilityMinima.subscriptionsPerFabric = InteractionModelEngine::GetInstance()->GetMinSubscriptionsPerFabric();
+ capabilityMinima.subscriptionsPerFabric = InteractionModelEngine::GetInstance()->GetMinGuaranteedSubscriptionsPerFabric();
 
  status = aEncoder.Encode(capabilityMinima);
  break;