From 4b6e228e297b73451f3a4b12fb7d0b24d9d32e6f Mon Sep 17 00:00:00 2001
From: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Date: Thu, 2 Jan 2020 15:00:57 -0800
Subject: [PATCH] Bluetooth: Auto tune if input MTU is set to 0
Git-commit: 4b6e228e297b73451f3a4b12fb7d0b24d9d32e6f
Patch-mainline: v5.6-rc1
References: jsc#SLE-13430

This enables the code to set the input MTU using the underline link
packet types when set to 0, previously this would likely be rejected by
the remote peer since it would be bellow the minimal of 48 for BR/EDR
or 23 for LE, that way it shall be safe to use 0 without causing any
side effects.

This is convenient for the likes of A2DP transport, see:

https://habr.com/en/post/456182/

Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 net/bluetooth/l2cap_core.c | 54 ++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 52 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index a845786258a0..1bca608e0170 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -1289,6 +1289,9 @@ static void l2cap_le_connect(struct l2cap_chan *chan)
 	if (test_and_set_bit(FLAG_LE_CONN_REQ_SENT, &chan->flags))
 		return;
 
+	if (!chan->imtu)
+		chan->imtu = chan->conn->mtu;
+
 	l2cap_le_flowctl_init(chan, 0);
 
 	req.psm     = chan->psm;
@@ -3226,6 +3229,49 @@ static inline void l2cap_txwin_setup(struct l2cap_chan *chan)
 	chan->ack_win = chan->tx_win;
 }
 
+static void l2cap_mtu_auto(struct l2cap_chan *chan)
+{
+	struct hci_conn *conn = chan->conn->hcon;
+
+	chan->imtu = L2CAP_DEFAULT_MIN_MTU;
+
+	/* The 2-DH1 packet has between 2 and 56 information bytes
+	 * (including the 2-byte payload header)
+	 */
+	if (!(conn->pkt_type & HCI_2DH1))
+		chan->imtu = 54;
+
+	/* The 3-DH1 packet has between 2 and 85 information bytes
+	 * (including the 2-byte payload header)
+	 */
+	if (!(conn->pkt_type & HCI_3DH1))
+		chan->imtu = 83;
+
+	/* The 2-DH3 packet has between 2 and 369 information bytes
+	 * (including the 2-byte payload header)
+	 */
+	if (!(conn->pkt_type & HCI_2DH3))
+		chan->imtu = 367;
+
+	/* The 3-DH3 packet has between 2 and 554 information bytes
+	 * (including the 2-byte payload header)
+	 */
+	if (!(conn->pkt_type & HCI_3DH3))
+		chan->imtu = 552;
+
+	/* The 2-DH5 packet has between 2 and 681 information bytes
+	 * (including the 2-byte payload header)
+	 */
+	if (!(conn->pkt_type & HCI_2DH5))
+		chan->imtu = 679;
+
+	/* The 3-DH5 packet has between 2 and 1023 information bytes
+	 * (including the 2-byte payload header)
+	 */
+	if (!(conn->pkt_type & HCI_3DH5))
+		chan->imtu = 1021;
+}
+
 static int l2cap_build_conf_req(struct l2cap_chan *chan, void *data, size_t data_size)
 {
 	struct l2cap_conf_req *req = data;
@@ -3255,8 +3301,12 @@ static int l2cap_build_conf_req(struct l2cap_chan *chan, void *data, size_t data
 	}
 
 done:
-	if (chan->imtu != L2CAP_DEFAULT_MTU)
-		l2cap_add_conf_opt(&ptr, L2CAP_CONF_MTU, 2, chan->imtu, endptr - ptr);
+	if (chan->imtu != L2CAP_DEFAULT_MTU) {
+		if (!chan->imtu)
+			l2cap_mtu_auto(chan);
+		l2cap_add_conf_opt(&ptr, L2CAP_CONF_MTU, 2, chan->imtu,
+				   endptr - ptr);
+	}
 
 	switch (chan->mode) {
 	case L2CAP_MODE_BASIC:
-- 
2.16.4