Re: [Bugme-new] [Bug 30092] New: smsc911x.c drops long packets with VLAN tags

[Andrew Morton <akpm@linux-foundation.org>]

(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.
> 

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