Bluetooth: ATT: Internalize ATT PDU TX pool

Why?
- metadata is easier to manage as an array + index
  - less error-prone -> less memory-management bugs
- we can. because of the previous refactor
- PDU allocations are more predictable
- ATT buffer size can be optimized by app
- isolates ATT from the rest of the ACL users
  - decouples ATT PDU size from e.g. SMP w/ LESC

Drawbacks:
- higher memory usage
- kconfig change

The higher memory use is only temporary, as this will be followed-up
with more refactors that should bring it back down.

Signed-off-by: Jonathan Rico <[email protected]>
Co-authored-by: Aleksander Wasaznik <[email protected]>

doc/releases/migration-guide-3.6.rst

@@ -185,6 +185,9 @@ Bootloader
 Bluetooth
 =========
 
+* ATT now has its own TX buffer pool.
+  If extra ATT buffers were configured using :kconfig:option:`CONFIG_BT_L2CAP_TX_BUF_COUNT`,
+  they now instead should be configured through :kconfig:option:`CONFIG_BT_ATT_TX_COUNT`.
 * The HCI implementation for both the Host and the Controller sides has been
   renamed for the IPC transport. The ``CONFIG_BT_RPMSG`` Kconfig option is now
   :kconfig:option:`CONFIG_BT_HCI_IPC`, and the ``zephyr,bt-hci-rpmsg-ipc``

include/zephyr/bluetooth/gatt.h

@@ -1336,7 +1336,7 @@ struct bt_gatt_exchange_params {
  *  @retval -ENOMEM ATT request queue is full and blocking would cause deadlock.
  *  Allow a pending request to resolve before retrying, or call this function
  *  outside the BT RX thread to get blocking behavior. Queue size is controlled
- *  by @kconfig{CONFIG_BT_L2CAP_TX_BUF_COUNT}.
+ *  by @kconfig{CONFIG_BT_ATT_TX_COUNT}.
  *
  *  @retval -EALREADY The MTU exchange procedure has been already performed.
  */
@@ -1502,7 +1502,7 @@ struct bt_gatt_discover_params {
  *  @retval -ENOMEM ATT request queue is full and blocking would cause deadlock.
  *  Allow a pending request to resolve before retrying, or call this function
  *  outside the BT RX thread to get blocking behavior. Queue size is controlled
- *  by @kconfig{CONFIG_BT_L2CAP_TX_BUF_COUNT}.
+ *  by @kconfig{CONFIG_BT_ATT_TX_COUNT}.
  */
 int bt_gatt_discover(struct bt_conn *conn,
 		     struct bt_gatt_discover_params *params);
@@ -1617,7 +1617,7 @@ struct bt_gatt_read_params {
  *  @retval -ENOMEM ATT request queue is full and blocking would cause deadlock.
  *  Allow a pending request to resolve before retrying, or call this function
  *  outside the BT RX thread to get blocking behavior. Queue size is controlled
- *  by @kconfig{CONFIG_BT_L2CAP_TX_BUF_COUNT}.
+ *  by @kconfig{CONFIG_BT_ATT_TX_COUNT}.
  */
 int bt_gatt_read(struct bt_conn *conn, struct bt_gatt_read_params *params);
 
@@ -1670,7 +1670,7 @@ struct bt_gatt_write_params {
  *  @retval -ENOMEM ATT request queue is full and blocking would cause deadlock.
  *  Allow a pending request to resolve before retrying, or call this function
  *  outside Bluetooth event context to get blocking behavior. Queue size is
- *  controlled by @kconfig{CONFIG_BT_L2CAP_TX_BUF_COUNT}.
+ *  controlled by @kconfig{CONFIG_BT_ATT_TX_COUNT}.
  */
 int bt_gatt_write(struct bt_conn *conn, struct bt_gatt_write_params *params);
 
@@ -1707,7 +1707,7 @@ int bt_gatt_write(struct bt_conn *conn, struct bt_gatt_write_params *params);
  *  @retval -ENOMEM ATT request queue is full and blocking would cause deadlock.
  *  Allow a pending request to resolve before retrying, or call this function
  *  outside the BT RX thread to get blocking behavior. Queue size is controlled
- *  by @kconfig{CONFIG_BT_L2CAP_TX_BUF_COUNT}.
+ *  by @kconfig{CONFIG_BT_ATT_TX_COUNT}.
  */
 int bt_gatt_write_without_response_cb(struct bt_conn *conn, uint16_t handle,
 				      const void *data, uint16_t length,
@@ -1733,7 +1733,7 @@ int bt_gatt_write_without_response_cb(struct bt_conn *conn, uint16_t handle,
  *  @retval -ENOMEM ATT request queue is full and blocking would cause deadlock.
  *  Allow a pending request to resolve before retrying, or call this function
  *  outside the BT RX thread to get blocking behavior. Queue size is controlled
- *  by @kconfig{CONFIG_BT_L2CAP_TX_BUF_COUNT}.
+ *  by @kconfig{CONFIG_BT_ATT_TX_COUNT}.
  */
 static inline int bt_gatt_write_without_response(struct bt_conn *conn,
 						 uint16_t handle, const void *data,
@@ -1895,7 +1895,7 @@ struct bt_gatt_subscribe_params {
  *  @retval -ENOMEM ATT request queue is full and blocking would cause deadlock.
  *  Allow a pending request to resolve before retrying, or call this function
  *  outside the BT RX thread to get blocking behavior. Queue size is controlled
- *  by @kconfig{CONFIG_BT_L2CAP_TX_BUF_COUNT}.
+ *  by @kconfig{CONFIG_BT_ATT_TX_COUNT}.
  */
 int bt_gatt_subscribe(struct bt_conn *conn,
 		      struct bt_gatt_subscribe_params *params);
@@ -1941,7 +1941,7 @@ int bt_gatt_resubscribe(uint8_t id, const bt_addr_le_t *peer,
  *  @retval -ENOMEM ATT request queue is full and blocking would cause deadlock.
  *  Allow a pending request to resolve before retrying, or call this function
  *  outside the BT RX thread to get blocking behavior. Queue size is controlled
- *  by @kconfig{CONFIG_BT_L2CAP_TX_BUF_COUNT}.
+ *  by @kconfig{CONFIG_BT_ATT_TX_COUNT}.
  */
 int bt_gatt_unsubscribe(struct bt_conn *conn,
 			struct bt_gatt_subscribe_params *params);

samples/bluetooth/tmap_bmr/prj.conf

@@ -8,7 +8,7 @@ CONFIG_UTF8=y
 
 CONFIG_BT_SMP=y
 CONFIG_BT_KEYS_OVERWRITE_OLDEST=y
-CONFIG_BT_L2CAP_TX_BUF_COUNT=20
+CONFIG_BT_ATT_TX_COUNT=20
 
 # TMAP support
 CONFIG_BT_TMAP=y

samples/bluetooth/tmap_peripheral/prj.conf

@@ -7,7 +7,7 @@ CONFIG_UTF8=y
 
 CONFIG_BT_SMP=y
 CONFIG_BT_KEYS_OVERWRITE_OLDEST=y
-CONFIG_BT_L2CAP_TX_BUF_COUNT=20
+CONFIG_BT_ATT_TX_COUNT=20
 
 # TMAP support
 CONFIG_BT_TMAP=y

subsys/bluetooth/audio/tbs_client.c

@@ -41,7 +41,7 @@ LOG_MODULE_REGISTER(bt_tbs_client, CONFIG_BT_TBS_CLIENT_LOG_LEVEL);
 	 IS_ENABLED(CONFIG_BT_TBS_CLIENT_CALL_FRIENDLY_NAME) +                                     \
 	 IS_ENABLED(CONFIG_BT_TBS_CLIENT_INCOMING_CALL))
 
-BUILD_ASSERT(CONFIG_BT_L2CAP_TX_BUF_COUNT >= TBS_CLIENT_BUF_COUNT, "Too few L2CAP buffers");
+BUILD_ASSERT(CONFIG_BT_ATT_TX_COUNT >= TBS_CLIENT_BUF_COUNT, "Too few ATT buffers");
 
 #include "common/bt_str.h"
 

subsys/bluetooth/host/Kconfig.gatt

@@ -5,6 +5,15 @@
 
 menu "ATT and GATT Options"
 
+config BT_ATT_TX_COUNT
+	int "Number of ATT buffers"
+	default BT_BUF_ACL_TX_COUNT
+	default 3
+	range 1 255
+	help
+	  These buffers are only used for sending anything over ATT.
+	  Requests, responses, indications, confirmations, notifications.
+
 config BT_ATT_PREPARE_COUNT
 	int "Number of ATT prepare write buffers"
 	default 0