Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 887f61a8 authored by Jakub Pawlowski's avatar Jakub Pawlowski
Browse files

Minimize amount of Flow Control packets for L2CAP CoC 

In order to not waste bandwidth on Flow Control packets with credits:
1. Set Initial Credits in the connect request/response to the maximum value
2. Send credits only when the remote has less than 64 of them left,
   increasing the value back to maximum.

Bug: 68359837
Test: observe data flow in btsnoop log
Change-Id: I34e1fecc55422b34df0b1e82bb2b402eb06620bd
parent 507f0d2f

system/stack/gap/gap_conn.cc

+5 −1
Original line number Diff line number Diff line
@@ -210,7 +210,7 @@ uint16_t GAP_ConnOpen(const char* p_serv_name, uint8_t service_id, 


  /* Configure L2CAP COC, if transport is LE */

  if (transport == BT_TRANSPORT_LE) {

    p_ccb->local_coc_cfg.credits = L2CAP_LE_DEFAULT_CREDIT;

    p_ccb->local_coc_cfg.credits = L2CAP_LE_CREDIT_DEFAULT;

    p_ccb->local_coc_cfg.mtu = p_cfg->mtu;



    uint16_t max_mps = controller_get_interface()->get_acl_data_size_ble();
@@ -219,6 +219,10 @@ uint16_t GAP_ConnOpen(const char* p_serv_name, uint8_t service_id, 
      le_mps = max_mps;

    }

    p_ccb->local_coc_cfg.mps = le_mps;



    VLOG(2) << __func__ << ": credits=" << p_ccb->local_coc_cfg.credits

            << ", mps=" << p_ccb->local_coc_cfg.mps

            << ", mtu=" << p_ccb->local_coc_cfg.mtu;

  }



  p_ccb->p_callback = p_cb;

system/stack/l2cap/l2c_api.cc

+8 −2
Original line number Diff line number Diff line
@@ -555,7 +555,10 @@ uint16_t L2CA_ConnectLECocReq(uint16_t psm, const RawAddress& p_bd_addr, 
  p_ccb->p_rcb = p_rcb;



  /* Save the configuration */

  if (p_cfg) memcpy(&p_ccb->local_conn_cfg, p_cfg, sizeof(tL2CAP_LE_CFG_INFO));

  if (p_cfg) {

    memcpy(&p_ccb->local_conn_cfg, p_cfg, sizeof(tL2CAP_LE_CFG_INFO));

    p_ccb->remote_credit_count = p_cfg->credits;

  }



  /* If link is up, start the L2CAP connection */

  if (p_lcb->link_state == LST_CONNECTED) {
@@ -625,7 +628,10 @@ bool L2CA_ConnectLECocRsp(const RawAddress& p_bd_addr, uint8_t id, 
    return false;

  }



  if (p_cfg) memcpy(&p_ccb->local_conn_cfg, p_cfg, sizeof(tL2CAP_LE_CFG_INFO));

  if (p_cfg) {

    memcpy(&p_ccb->local_conn_cfg, p_cfg, sizeof(tL2CAP_LE_CFG_INFO));

    p_ccb->remote_credit_count = p_cfg->credits;

  }



  if (result == L2CAP_CONN_OK)

    l2c_csm_execute(p_ccb, L2CEVT_L2CA_CONNECT_RSP, NULL);

system/stack/l2cap/l2c_csm.cc

+1 −1
Original line number Diff line number Diff line
@@ -1105,7 +1105,7 @@ static void l2c_csm_open(tL2C_CCB* p_ccb, uint16_t event, void* p_data) { 
    case L2CEVT_L2CAP_RECV_FLOW_CONTROL_CREDIT:

      credit = (uint16_t*)p_data;

      L2CAP_TRACE_DEBUG("%s Credits received %d", __func__, *credit);

      if ((p_ccb->peer_conn_cfg.credits + *credit) > L2CAP_LE_MAX_CREDIT) {

      if ((p_ccb->peer_conn_cfg.credits + *credit) > L2CAP_LE_CREDIT_MAX) {

        /* we have received credits more than max coc credits,

         * so disconnecting the Le Coc Channel

         */

system/stack/l2cap/l2c_int.h

+19 −6
Original line number Diff line number Diff line
@@ -37,12 +37,21 @@ 
#define L2CAP_MIN_MTU 48 /* Minimum acceptable MTU is 48 bytes */



/* LE credit based L2CAP connection parameters */

#define L2CAP_LE_MIN_MTU 23

#define L2CAP_LE_MIN_MPS 23

#define L2CAP_LE_MAX_MPS 65533

#define L2CAP_LE_MIN_CREDIT 0

#define L2CAP_LE_MAX_CREDIT 65535

#define L2CAP_LE_DEFAULT_CREDIT 1

constexpr uint16_t L2CAP_LE_MIN_MTU = 23;  // Minimum SDU size

constexpr uint16_t L2CAP_LE_MIN_MPS = 23;

constexpr uint16_t L2CAP_LE_MAX_MPS = 65533;

constexpr uint16_t L2CAP_LE_CREDIT_MAX = 65535;



// This is initial amout of credits we send, and amount to which we increase

// credits once they fall below threshold

constexpr uint16_t L2CAP_LE_CREDIT_DEFAULT = 0xffff;



// If credit count on remote fall below this value, we send back credits to

// reach default value.

constexpr uint16_t L2CAP_LE_CREDIT_THRESHOLD = 0x0040;



static_assert(L2CAP_LE_CREDIT_THRESHOLD < L2CAP_LE_CREDIT_DEFAULT,

              "Threshold must be smaller then default credits");



/*

 * Timeout values (in milliseconds).
@@ -327,6 +336,10 @@ typedef struct t_l2c_ccb { 
  uint16_t fixed_chnl_idle_tout; /* Idle timeout to use for the fixed channel */

#endif

  uint16_t tx_data_len;



  /* Number of LE frames that the remote can send to us (credit count in

   * remote). Valid only for LE CoC */

  uint16_t remote_credit_count;

} tL2C_CCB;



/***********************************************************************

system/stack/l2cap/l2c_main.cc

+12 −3
Original line number Diff line number Diff line
@@ -215,9 +215,18 @@ void l2c_rcv_acl_data(BT_HDR* p_msg) { 


  if (p_lcb->transport == BT_TRANSPORT_LE) {

    l2c_lcc_proc_pdu(p_ccb, p_msg);

    // Got a pkt, valid send out credits to the peer device

    uint16_t credit = L2CAP_LE_DEFAULT_CREDIT;

    l2c_csm_execute(p_ccb, L2CEVT_L2CA_SEND_FLOW_CONTROL_CREDIT, &credit);



    /* The remote device has one less credit left */

    --p_ccb->remote_credit_count;



    /* If the credits left on the remote device are getting low, send some */

    if (p_ccb->remote_credit_count <= L2CAP_LE_CREDIT_THRESHOLD) {

      uint16_t credits = L2CAP_LE_CREDIT_DEFAULT - p_ccb->remote_credit_count;

      p_ccb->remote_credit_count = L2CAP_LE_CREDIT_DEFAULT;



      /* Return back credits */

      l2c_csm_execute(p_ccb, L2CEVT_L2CA_SEND_FLOW_CONTROL_CREDIT, &credits);

    }

  } else {

    /* Basic mode packets go straight to the state machine */

    if (p_ccb->peer_cfg.fcr.mode == L2CAP_FCR_BASIC_MODE)