From f8f02740acdf4d302d5c2f91ee2e34444d405671 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C5=81ukasz=20Rymanowski?= <lukasz.rymanowski@codecoup.pl>
Date: Tue, 12 Mar 2019 13:13:12 +0100
Subject: [PATCH] nimble/host: Fix credits setting for L2CAP CoC

With current implementation we could end up having credits 0 when
requested L2CAP CoC MTU is much lower than MTU on L2CAP channel.

This patch fixes it.
---
 nimble/host/src/ble_l2cap_coc.c       |  5 ++++-
 nimble/host/test/src/ble_l2cap_test.c | 22 ++++++++++++++++++----
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/nimble/host/src/ble_l2cap_coc.c b/nimble/host/src/ble_l2cap_coc.c
index 4dd2a9356..61345f5af 100644
--- a/nimble/host/src/ble_l2cap_coc.c
+++ b/nimble/host/src/ble_l2cap_coc.c
@@ -255,7 +255,10 @@ ble_l2cap_coc_chan_alloc(uint16_t conn_handle, uint16_t psm, uint16_t mtu,
     /* Number of credits should allow to send full SDU with on given
      * L2CAP MTU
      */
-    chan->coc_rx.credits = (mtu + (chan->my_mtu - 1) / 2) / chan->my_mtu;
+    chan->coc_rx.credits = mtu / chan->my_mtu;
+    if (mtu % chan->my_mtu) {
+        chan->coc_rx.credits++;
+    }
 
     chan->initial_credits = chan->coc_rx.credits;
     return chan;
diff --git a/nimble/host/test/src/ble_l2cap_test.c b/nimble/host/test/src/ble_l2cap_test.c
index e0c537ffc..106b9f68b 100644
--- a/nimble/host/test/src/ble_l2cap_test.c
+++ b/nimble/host/test/src/ble_l2cap_test.c
@@ -719,6 +719,18 @@ ble_l2cap_test_event(struct ble_l2cap_event *event, void *arg)
     }
 }
 
+static uint16_t ble_l2cap_calculate_credits(uint16_t mtu, uint16_t mps)
+{
+    int credits;
+
+    credits = mtu / mps;
+    if (mtu % mps) {
+        credits++;
+    }
+
+    return credits;
+}
+
 static void
 ble_l2cap_test_coc_connect(struct test_data *t)
 {
@@ -747,8 +759,9 @@ ble_l2cap_test_coc_connect(struct test_data *t)
         return;
     }
 
-    req.credits = htole16((t->mtu + (MYNEWT_VAL(BLE_L2CAP_COC_MTU) - 1) / 2) /
-                                                MYNEWT_VAL(BLE_L2CAP_COC_MTU));
+    req.credits = htole16(
+                        ble_l2cap_calculate_credits(t->mtu,
+                                                    MYNEWT_VAL(BLE_L2CAP_COC_MTU)));
     req.mps = htole16(MYNEWT_VAL(BLE_L2CAP_COC_MTU));
     req.mtu = htole16(t->mtu);
     req.psm = htole16(t->psm);
@@ -812,8 +825,9 @@ ble_l2cap_test_coc_connect_by_peer(struct test_data *t)
         rsp.result = htole16(ev->l2cap_status);
     } else {
         /* Receive response from peer.*/
-        rsp.credits = htole16((t->mtu + (MYNEWT_VAL(BLE_L2CAP_COC_MTU) - 1) / 2) /
-                                                MYNEWT_VAL(BLE_L2CAP_COC_MTU));
+        rsp.credits = htole16(
+                            ble_l2cap_calculate_credits(t->mtu,
+                                                        MYNEWT_VAL(BLE_L2CAP_COC_MTU)));
         rsp.dcid = current_cid++;
         rsp.mps = htole16(MYNEWT_VAL(BLE_L2CAP_COC_MTU));
         rsp.mtu = htole16(t->mtu);