[RFC] mac80211: Fix MAX MTU Calculation

[Chaitanya <chaitanyatk@posedge.com>]

Fix the MTU calculation, we should check for data_len+ mesh hdr len
and shouldn't include any header lengths.

ToDo: Get the MAX_DATA_LEN based on driver's AMSDU capability.

Signed-off-by: T Krishna Chaitanya <chaitanyatk@posedge.com>

---

 net/mac80211/iface.c |   17 ++++++++++++++++-
 1 files changed, 16 insertions(+), 1 deletions(-)

diff --git a/net/mac80211/iface.c b/net/mac80211/iface.c
index 54fb7f9..da74ef9 100644
--- a/net/mac80211/iface.c
+++ b/net/mac80211/iface.c
@@ -214,8 +214,23 @@ static int ieee80211_change_mtu(struct net_device *dev, int new_mtu)
 
 	/* FIX: what would be proper limits for MTU?
 	 * This interface uses 802.3 frames. */
+	/* Fixed: MTU needn't worry about headers*/
+
+	/* 802.11-2012: 8.2.3: The maximum frame body size is determined by
+	1. The maximum MSDU size (2304 octets),
+	2. plus the length of the Mesh Control field (6, 12, or 18 octets)
+		if present,
+	3. the maximum unencrypted MMPDU size excluding the MAC header and
+		FCS (2304 octets) or
+	4. the maximum A- MSDU size (3839 or 7935 octets),
+		plus any overhead from security encapsulation.
+	Note1: IEEE80211_MAX_DATA_LEN doesnt include any headers (2304),
+		so it can be used directly+ Mesh HDR Len
+	Note2: In Other places (like skb_alloc) its handled properly.
+	 */
+
 	if (new_mtu < 256 ||
-	    new_mtu > IEEE80211_MAX_DATA_LEN - 24 - 6 - meshhdrlen) {
+	    new_mtu > IEEE80211_MAX_DATA_LEN + meshhdrlen) {
 		return -EINVAL;
 	}