The previous value of 672 for L2CAP_DEFAULT_MAX_PDU_SIZE is based on the default L2CAP MTU. That default MTU is calculated from the size of two DH5 packets, minus ACL and L2CAP b-frame header overhead.
ERTM is used with newer basebands that typically support larger 3-DH5 packets, and i-frames and s-frames have more header overhead. With clean RF conditions, basebands will typically attempt to use 1021-byte 3-DH5 packets for maximum throughput. Adjusting for 2 bytes of ACL headers plus 10 bytes of worst-case L2CAP headers yields 1009 bytes of payload. This PDU size imposes less overhead for header bytes and gives the baseband the option to choose 3-DH5 packets, but is small enough for ERTM traffic to interleave well with other L2CAP or SCO data. 672-byte payloads do not allow the most efficient over-the-air packet choice, and cannot achieve maximum throughput over BR/EDR. Signed-off-by: Mat Martineau <[email protected]> --- include/net/bluetooth/l2cap.h | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h index 16e412f..6c24144 100644 --- a/include/net/bluetooth/l2cap.h +++ b/include/net/bluetooth/l2cap.h @@ -35,7 +35,7 @@ #define L2CAP_DEFAULT_MAX_TX 3 #define L2CAP_DEFAULT_RETRANS_TO 2000 /* 2 seconds */ #define L2CAP_DEFAULT_MONITOR_TO 12000 /* 12 seconds */ -#define L2CAP_DEFAULT_MAX_PDU_SIZE 672 +#define L2CAP_DEFAULT_MAX_PDU_SIZE 1009 /* Sized for 3-DH5 packet */ #define L2CAP_DEFAULT_ACK_TO 200 #define L2CAP_LOCAL_BUSY_TRIES 12 -- 1.7.1 -- Mat Martineau Employee of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
