Bluetooth: Controller: Kconfig: Allow limiting max tx octets below 27

Define BT_CTLR_MIN_VAL_OF_MAX_ACL_TX_PAYLOAD_DEFAULT to allow setting the maximum number of tx octets to a value lower than 27 bytes. We only allow using this with devices supporting ISO as there is a risk of not being interoperable with older devices. Signed-off-by: Rubin Gerritsen <[email protected]>
DatGizmo · Nov 23, 2023 · 2cd0e2a · 2cd0e2a
1 parent 4ca4e9f
commit 2cd0e2a
Show file tree

Hide file tree

Showing 2 changed files with 34 additions and 0 deletions.
diff --git a/subsys/bluetooth/controller/Kconfig b/subsys/bluetooth/controller/Kconfig
@@ -154,6 +154,26 @@ config BT_CTLR_SDC_CENTRAL_ACL_EVENT_SPACING_DEFAULT
 	  timeline if the connection interval is longer than the ACL event spacing.
 	  This gap can be used for other scheduling activites like isochronous streams.
 
+config BT_CTLR_MIN_VAL_OF_MAX_ACL_TX_PAYLOAD_DEFAULT
+	int "Default minimum value that will be used as maximum Tx octets for ACL connections"
+	default 27
+	range 10 27
+	depends on BT_ISO && BT_CONN
+	help
+	  This configuration sets the minimum value of maximum ACL payload length that can be sent
+	  in each packet. If the configured event length is shorter than what is required to
+	  send a packet pair of 27 bytes in each direction, the controller will use this value to
+	  determine how much it can reduce the payload size to satisfy the event length requirements.
+	  LL Control PDUs are not affected by this API.
+	  Together with BT_CTLR_SDC_MAX_CONN_EVENT_LEN_DEFAULT this allows the controller to schedule
+	  ACLs events closer together with other activities.
+	  Setting this parameter to a lower value will result in more link layer fragmentation,
+	  reducing the maximum throughput.
+	  Setting this parameter to a value lower than 27 bytes may result in interoperability
+	  issues with older Bluetooth products. It is therefore not recommended to use this API
+	  for applications interacting with devices qualified for Bluetooth Specification 5.1 or
+	  older.
+
 config BT_CTLR_SDC_PERIODIC_ADV_EVENT_LEN_DEFAULT_OVERRIDE
 	bool "Override periodic adv event length default"
 

diff --git a/subsys/bluetooth/controller/hci_driver.c b/subsys/bluetooth/controller/hci_driver.c
@@ -1238,6 +1238,20 @@ static int hci_driver_open(void)
 		}
 	}
 
+#if defined(BT_CTLR_MIN_VAL_OF_MAX_ACL_TX_PAYLOAD_DEFAULT)
+	if (CONFIG_BT_CTLR_MIN_VAL_OF_MAX_ACL_TX_PAYLOAD_DEFAULT != 27) {
+		sdc_hci_cmd_vs_min_val_of_max_acl_tx_payload_set_t params = {
+			.min_val_of_max_acl_tx_payload =
+				CONFIG_config BT_CTLR_MIN_VAL_OF_MAX_ACL_TX_PAYLOAD_DEFAULT
+		};
+		err = sdc_hci_cmd_vs_min_val_of_max_acl_tx_payload_set(&params);
+		if (err) {
+			MULTITHREADING_LOCK_RELEASE();
+			return -ENOTSUP;
+		}
+	}
+#endif
+
 	MULTITHREADING_LOCK_RELEASE();
 
 	return 0;