netdev - [RFC PATCH] drivers/net/tg3.c: Raise Jumbo Frame MTU to 9216?

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Message-ID: <1284572516.10223.12.camel@Joe-Laptop>
Date:	Wed, 15 Sep 2010 10:41:56 -0700
From:	Joe Perches <joe@...ches.com>
To:	Matt Carlson <mcarlson@...adcom.com>,
	Michael Chan <mchan@...adcom.com>,
	Benjamin Li <benli@...adcom.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [RFC PATCH] drivers/net/tg3.c: Raise Jumbo Frame MTU to 9216?

The TG3 apparently supports 9K frame sizes.

http://www.broadcom.com/collateral/pb/5704C-PB05-R.pdf

Is exactly 9000 a hardware limit?

Should the jumbo frame MTU be raised to 9216 or 9216
less the size of MAC, VLAN, IP and TCP headers?

diff --git a/drivers/net/tg3.c b/drivers/net/tg3.c
index 9f6ffff..3727070 100644
--- a/drivers/net/tg3.c
+++ b/drivers/net/tg3.c
@@ -95,7 +95,7 @@
 /* hardware minimum and maximum for a single frame's data payload */
 #define TG3_MIN_MTU			60
 #define TG3_MAX_MTU(tp)	\
-	((tp->tg3_flags & TG3_FLAG_JUMBO_CAPABLE) ? 9000 : 1500)
+	((tp->tg3_flags & TG3_FLAG_JUMBO_CAPABLE) ? 9216 : 1500)
 
 /* These numbers seem to be hard coded in the NIC firmware somehow.
  * You can't change the ring sizes, but you can change where you place


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