Bluetooth: Add CONFIG_BT_LE_L2CAP_ECRED

This adds CONFIG_BT_LE_L2CAP_ECRED which can be used to enable L2CAP
Enhanced Credit Flow Control Mode by default, previously it was only
possible to set it via module parameter (e.g. bluetooth.enable_ecred=1).

Since L2CAP ECRED mode is required by the likes of EATT which is
recommended for LE Audio this enables it by default.
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Tested-By: Tedd Ho-Jeong An <tedd.an@intel.com>

net/bluetooth/Kconfig

@@ -78,6 +78,17 @@ config BT_LE
 	  Bluetooth Low Energy includes support low-energy physical
 	  layer available with Bluetooth version 4.0 or later.
 
+config BT_LE_L2CAP_ECRED
+	bool "Bluetooth L2CAP Enhanced Credit Flow Control"
+	depends on BT_LE
+	default y
+	help
+	  Bluetooth Low Energy L2CAP Enhanced Credit Flow Control available with
+	  Bluetooth version 5.2 or later.
+
+	  This can be overridden by passing bluetooth.enable_ecred=[1|0]
+	  on the kernel commandline.
+
 config BT_6LOWPAN
 	tristate "Bluetooth 6LoWPAN support"
 	depends on BT_LE && 6LOWPAN

net/bluetooth/l2cap_core.c

@@ -45,7 +45,7 @@
 #define LE_FLOWCTL_MAX_CREDITS 65535
 
 bool disable_ertm;
-bool enable_ecred;
+bool enable_ecred = IS_ENABLED(CONFIG_BT_LE_L2CAP_ECRED);
 
 static u32 l2cap_feat_mask = L2CAP_FEAT_FIXED_CHAN | L2CAP_FEAT_UCD;