The smsc911x.c driver can't receive packets of the maximum MTU if they have a 802.1q tag. Testing with ping -s 1500 shows that the frame with the first IP segment is dropped. The source of the problem is this line at smsc911x.c:1023 (smsc911x_poll): if (unlikely(rxstat & RX_STS_ES_)) { The datasheet at http://www.smsc.com/media/Downloads_Public/Data_Sheets/9221.pdf describes this bit as a logical OR of bits 11, 7, 6 and 1. The problem is that bit 7 is set if the packet is longer than 1518 bytes, which is true for the 802.1q tagged packets. As a quick and dirty solution, I replaced RX_STS_ES_ with (1<<11|1<<6|1<<1), and now 802.1q tagged packets are received just fine. This was tested on an IGEPv2, which has a SMSC LAN9221i.
(switched to email. Please respond via emailed reply-to-all, not via the bugzilla web interface). On Mon, 28 Feb 2011 15:57:14 GMT bugzilla-daemon@bugzilla.kernel.org wrote: > https://bugzilla.kernel.org/show_bug.cgi?id=30092 > > Summary: smsc911x.c drops long packets with VLAN tags > Product: Drivers > Version: 2.5 > Kernel Version: 2.6.36.4 > Platform: All > OS/Version: Linux > Tree: Mainline > Status: NEW > Severity: normal > Priority: P1 > Component: Network > AssignedTo: drivers_network@kernel-bugs.osdl.org > ReportedBy: weinholt@csbnet.se > Regression: No > > > The smsc911x.c driver can't receive packets of the maximum MTU if they have a > 802.1q tag. Testing with ping -s 1500 shows that the frame with the first IP > segment is dropped. > > The source of the problem is this line at smsc911x.c:1023 (smsc911x_poll): > > if (unlikely(rxstat & RX_STS_ES_)) { > > The datasheet at > http://www.smsc.com/media/Downloads_Public/Data_Sheets/9221.pdf describes > this > bit as a logical OR of bits 11, 7, 6 and 1. The problem is that bit 7 is set > if > the packet is longer than 1518 bytes, which is true for the 802.1q tagged > packets. As a quick and dirty solution, I replaced RX_STS_ES_ with > (1<<11|1<<6|1<<1), and now 802.1q tagged packets are received just fine. > > This was tested on an IGEPv2, which has a SMSC LAN9221i. > Thanks. Become famous, get more girls: send us a patch as per Documentation/SubmittingPatches :)
Andrew Morton <akpm@linux-foundation.org> writes: > (switched to email. Please respond via emailed reply-to-all, not via the > bugzilla web interface). > > On Mon, 28 Feb 2011 15:57:14 GMT > bugzilla-daemon@bugzilla.kernel.org wrote: > >> https://bugzilla.kernel.org/show_bug.cgi?id=30092 >> > Thanks. Become famous, get more girls: send us a patch as per > Documentation/SubmittingPatches :) There's a register called VLAN1 that wasn't being configured. Setting it to 0x8100 fixes the problem I reported. There's also a VLAN2 register, possibly meant for stacked VLANs, but the description in the datasheet doesn't make sense to me, and I can't test stacked VLANs, so I'm not going to change it. Subject: [PATCH] net/smsc911x.c: Set the VLAN1 register to fix VLAN MTU problem From: Göran Weinholt <weinholt@csbnet.se> The smsc911x driver would drop frames longer than 1518 bytes, which is a problem for networks with VLAN tagging. The VLAN1 tag register is used to increase the legal frame size to 1522 when a VLAN tag is identified. Signed-off-by: Göran Weinholt <weinholt@csbnet.se> --- diff -uprN linux-2.6.36.4-vanilla/drivers/net/smsc911x.c linux-2.6.36.4/drivers/net/smsc911x.c --- linux-2.6.36.4-vanilla/drivers/net/smsc911x.c 2011-02-18 00:14:38.000000000 +0100 +++ linux-2.6.36.4/drivers/net/smsc911x.c 2011-03-02 14:29:11.884382251 +0100 @@ -1178,6 +1178,11 @@ static int smsc911x_open(struct net_devi smsc911x_reg_write(pdata, HW_CFG, 0x00050000); smsc911x_reg_write(pdata, AFC_CFG, 0x006E3740); + /* Increase the legal frame size of VLAN tagged frames to 1522 bytes */ + spin_lock_irq(&pdata->mac_lock); + smsc911x_mac_write(pdata, VLAN1, ETH_P_8021Q); + spin_unlock_irq(&pdata->mac_lock); + /* Make sure EEPROM has finished loading before setting GPIO_CFG */ timeout = 50; while ((smsc911x_reg_read(pdata, E2P_CMD) & E2P_CMD_EPC_BUSY_) &&
From: weinholt@csbnet.se (Göran Weinholt) Date: Wed, 02 Mar 2011 15:07:21 +0100 > Subject: [PATCH] net/smsc911x.c: Set the VLAN1 register to fix VLAN MTU > problem > From: Göran Weinholt <weinholt@csbnet.se> > > The smsc911x driver would drop frames longer than 1518 bytes, which is a > problem for networks with VLAN tagging. The VLAN1 tag register is used > to increase the legal frame size to 1522 when a VLAN tag is identified. > > Signed-off-by: Göran Weinholt <weinholt@csbnet.se> Applied, thanks.
Reply-To: Steve.Glendinning@smsc.com > > Subject: [PATCH] net/smsc911x.c: Set the VLAN1 register to fix VLAN MTU problem > > From: Göran Weinholt <weinholt@csbnet.se> > > > > The smsc911x driver would drop frames longer than 1518 bytes, which is a > > problem for networks with VLAN tagging. The VLAN1 tag register is used > > to increase the legal frame size to 1522 when a VLAN tag is identified. > > > > Signed-off-by: Göran Weinholt <weinholt@csbnet.se> > > Applied, thanks. Thanks David, I was just about to ack this but you beat me to it :-) As Göran said, the datasheet is a little vague. I've checked here, and there aren't any bad implications of always turning this option on. Acked-by: Steve Glendinning <steve.glendinning@smsc.com>