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Bluetooth: Host: Fix redundant ACL Rx buffer count #99152

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Bluetooth: Host: Fix redundant ACL Rx buffer count #99152

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9d48d51
Bluetooth: Controller: Fix define in HCI Command Tx Count calculation
cvinayak Nov 10, 2025
e85b163
Bluetooth: Host: Fix redundant ACL Rx buffer allocation
cvinayak Nov 10, 2025
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37 changes: 31 additions & 6 deletions include/zephyr/bluetooth/buf.h
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Original file line number Diff line number Diff line change
Expand Up @@ -151,12 +151,25 @@ static inline enum bt_buf_type bt_buf_type_from_h4(uint8_t h4_type, enum bt_buf_
* re-assembly into, and if all links are re-assembling, there will be no buffer
* available for the HCI driver to allocate from.
*/
#define BT_BUF_ACL_RX_COUNT_EXTRA CONFIG_BT_BUF_ACL_RX_COUNT_EXTRA
#define BT_BUF_ACL_RX_COUNT (1 + BT_BUF_ACL_RX_COUNT_EXTRA)
#else
#define BT_BUF_ACL_RX_COUNT_EXTRA 0
#define BT_BUF_ACL_RX_COUNT 0
#endif /* CONFIG_BT_CONN && CONFIG_BT_HCI_HOST */
#define BT_BUF_ACL_RX_COUNT_RESERVED 1

/* Host will block unreferencing one Rx buffer per active ACL connection and generate HCI Host
* Number of Completed packets for the rest. This means new HCI data packets will be generated by
* the Controller minus the minimum number of Rx buffer count blocked unreferencing in the Host.
*/
#define BT_BUF_ACL_RX_COUNT_BLOCKED_MIN 1
#define BT_BUF_ACL_RX_COUNT_BLOCKED_MAX CONFIG_BT_MAX_CONN

/* To avoid deadlock, account for maximum Rx buffers blocked in the Host */
#define BT_BUF_ACL_RX_COUNT_EXTRA MAX(BT_BUF_ACL_RX_COUNT_BLOCKED_MAX, \
CONFIG_BT_BUF_ACL_RX_COUNT_EXTRA)
/* ACL Rx Buffers being processed by the Host */
#define BT_BUF_ACL_RX_COUNT (BT_BUF_ACL_RX_COUNT_RESERVED + BT_BUF_ACL_RX_COUNT_EXTRA)

#else /* !CONFIG_BT_CONN || !CONFIG_BT_HCI_HOST */
#define BT_BUF_ACL_RX_COUNT_EXTRA 0
#define BT_BUF_ACL_RX_COUNT 0
#endif /* !CONFIG_BT_CONN || !CONFIG_BT_HCI_HOST */

BUILD_ASSERT(BT_BUF_ACL_RX_COUNT <= BT_BUF_ACL_RX_COUNT_MAX,
"Maximum number of ACL RX buffer is 65535, reduce CONFIG_BT_BUF_ACL_RX_COUNT_EXTRA");
Expand All @@ -171,9 +184,21 @@ BUILD_ASSERT(BT_BUF_ACL_RX_COUNT <= BT_BUF_ACL_RX_COUNT_MAX,
BUILD_ASSERT(CONFIG_BT_BUF_EVT_RX_COUNT > CONFIG_BT_BUF_ACL_TX_COUNT,
"Increase Event RX buffer count to be greater than ACL TX buffer count");

#if defined(CONFIG_BT_HCI_ACL_FLOW_CONTROL)
/* TODO: Introduce Kconfig option to replace BT_BUF_HCI_ACL_RX_COUNT. For now, lets use minimum one
* Rx buffer for each active ACL connection in addition to one each blocked unreferencing in the
* Host per active ACL connection.
*
* We do not want the use of CONFIG_BT_BUF_EVT_RX_COUNT in the derivation of
* BT_BUF_HCI_ACL_RX_COUNT.
*/
#define BT_BUF_RX_COUNT ((CONFIG_BT_MAX_CONN + 1U) + BT_BUF_ACL_RX_COUNT)

#else /* !CONFIG_BT_HCI_ACL_FLOW_CONTROL */
/** Buffer count needed for HCI ACL or HCI ISO plus Event RX buffers */
#define BT_BUF_RX_COUNT (CONFIG_BT_BUF_EVT_RX_COUNT + \
MAX(BT_BUF_ACL_RX_COUNT, BT_BUF_ISO_RX_COUNT))
#endif /* CONFIG_BT_HCI_ACL_FLOW_CONTROL */

/** Data size needed for HCI Command buffers. */
#define BT_BUF_CMD_TX_SIZE BT_BUF_CMD_SIZE(CONFIG_BT_BUF_CMD_TX_SIZE)
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29 changes: 19 additions & 10 deletions subsys/bluetooth/common/hci_common_internal.h
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Expand Up @@ -41,15 +41,13 @@ BUILD_ASSERT((CONFIG_BT_BUF_CMD_TX_COUNT == CONFIG_BT_CTLR_HCI_NUM_CMD_PKT_MAX),
*
* Host keeps the first, and subsequent, Rx buffers (that comes from the driver) for each connection
* to do re-assembly into, up to the L2CAP SDU length required number of Rx buffers.
* BT_BUF_ACL_RX_COUNT_EXTRA holds the application configured number of buffers across active
* connections for recombination of HCI data packets to L2CAP SDUs.
*
* BT_BUF_HCI_EVT_RX_COUNT defines the number of available buffers reserved for "synchronous"
* processing of HCI events like Number of Completed Packets, disconnection complete etc.
* BT_BUF_ACL_RX_COUNT_BLOCKED_MAX represents the maximum number of buffers that can be blocked
* across active connections for recombination of HCI data packets to L2CAP SDUs.
*
* BT_BUF_HCI_ACL_RX_COUNT defines the number of available buffers for Controller to Host data
* flow control; keeping the application configured BT_BUF_ACL_RX_COUNT_EXTRA number of buffers
* available for L2CAP recombination, and a reserved number of buffers for processing HCI events.
* available for L2CAP recombination, and BT_BUF_ACL_RX_COUNT_RESERVED reserved number of buffers
* for processing incoming HCI data packets.
*/

/* FIXME: Calculate the maximum number of HCI events of different types that a connection can
Expand All @@ -67,12 +65,23 @@ BUILD_ASSERT((CONFIG_BT_BUF_CMD_TX_COUNT == CONFIG_BT_CTLR_HCI_NUM_CMD_PKT_MAX),
* control to restrict buffers required on resource constraint devices, i.e. if these events are not
* processed "synchronous".
*/
#define BT_BUF_HCI_EVT_RX_COUNT 1
#define BT_BUF_HCI_ACL_RX_COUNT (BT_BUF_RX_COUNT - BT_BUF_HCI_EVT_RX_COUNT - \
BT_BUF_ACL_RX_COUNT_EXTRA)
#define BT_BUF_HCI_ACL_RX_COUNT (BT_BUF_RX_COUNT - BT_BUF_ACL_RX_COUNT_EXTRA)

/* During L2CAP recombination, maximum one Rx buffer per each active ACL connection can be held or
* blocked unreferencing in the Host, i.e. BT_BUF_ACL_RX_COUNT_BLOCKED_MAX.
*
* But at the instant of generating Host Number of Completed packets events a minimum of one Rx
* buffer is still blocked unreferencing, i.e. BT_BUF_ACL_RX_COUNT_BLOCKED_MIN.
*
* BT_BUF_HCI_ACL_RX_COUNT_EXTRA defines the outstanding number of HCI ACL data packets that the
* Controller can generate.
*/
#define BT_BUF_HCI_ACL_RX_COUNT_EXTRA (BT_BUF_HCI_ACL_RX_COUNT - BT_BUF_ACL_RX_COUNT_RESERVED - \
BT_BUF_ACL_RX_COUNT_BLOCKED_MIN)
#define BT_BUF_CMD_TX_HOST_NUM_CMPLT_PKT (BT_BUF_HCI_ACL_RX_COUNT)

#else /* !CONFIG_BT_HCI_ACL_FLOW_CONTROL */
#define BT_BUF_HCI_ACL_RX_COUNT_EXTRA 0
#define BT_BUF_CMD_TX_HOST_NUM_CMPLT_PKT 0
#endif /* !CONFIG_BT_HCI_ACL_FLOW_CONTROL */

Expand All @@ -97,6 +106,6 @@ BUILD_ASSERT(IS_ENABLED(CONFIG_BT_CTLR_HCI_NUM_CMD_PKT_MAX),
#define BT_BUF_HCI_ACL_RX_COUNT (BT_BUF_RX_COUNT)

/* Controller-only with Controller to Host data flow control */
#define BT_BUF_CMD_TX_COUNT (BT_BUF_RX_COUNT + CONFIG_BT_CTLR_HCI_NUM_CMD_PKT_MAX)
#define BT_BUF_CMD_TX_COUNT (BT_BUF_HCI_ACL_RX_COUNT + CONFIG_BT_CTLR_HCI_NUM_CMD_PKT_MAX)

#endif /* CONFIG_BT_HCI_ACL_FLOW_CONTROL */
10 changes: 7 additions & 3 deletions subsys/bluetooth/host/buf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -83,9 +83,13 @@ static void evt_pool_destroy(struct net_buf *buf)
buf_rx_freed_notify(BT_BUF_EVT);
}

NET_BUF_POOL_DEFINE(acl_in_pool, (BT_BUF_ACL_RX_COUNT_EXTRA + BT_BUF_HCI_ACL_RX_COUNT),
BT_BUF_ACL_SIZE(CONFIG_BT_BUF_ACL_RX_SIZE), sizeof(struct bt_conn_rx),
acl_in_pool_destroy);
/* Allocate Rx buffer count sufficient to block unreferencing one Rx buffer per active ACL
* connection, and additional HCI ACL data packets that the Controller can generate for the
* Host Number of Completed data packets count that the Host has given back to the Controller.
*/
NET_BUF_POOL_DEFINE(acl_in_pool, (BT_BUF_ACL_RX_COUNT_EXTRA + BT_BUF_HCI_ACL_RX_COUNT_EXTRA),
BT_BUF_ACL_SIZE(CONFIG_BT_BUF_ACL_RX_SIZE),
sizeof(struct bt_conn_rx), acl_in_pool_destroy);

NET_BUF_POOL_FIXED_DEFINE(evt_pool, CONFIG_BT_BUF_EVT_RX_COUNT, BT_BUF_EVT_RX_SIZE, 0,
evt_pool_destroy);
Expand Down
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