gianfar.c: Unwanted VLAN tagging on TX frames

gianfar.c: Unwanted VLAN tagging on TX frames

[Torsten Fleischer]

Hello everyone,

I have the Freescale's MPC8313erdb eval board and run the latest stable linux
kernel version (linux-2.6.30.5).

After creating a VLAN device (e.g. eth0.2) a VLAN tag is also inserted into 
frames that don't relate to a VLAN device. This is the case for frames that 
are directly sent through a standard ethernet interface (e.g. eth0).

When creating a VLAN device the gianfar driver enables the  hardware supported 
VLAN tagging on TX frames. This is done by setting the VLINS bit of the TCTRL 
register inside the function gianfar_vlan_rx_register().
The problem is that every outgoing frame will be tagged.  For frames from an 
interface like eth0 the VLN bit of the FCB isn't set. Therefore the eTSEC uses 
the content of the Default VLAN control word register (DFVLAN) to tag the 
frame. As long as this register will not be modified after a reset of the 
controller the outgoing frames will be tagged with VID = 0 (priority tagged 
frames). 

The following patch solves this problem.

diff -uprN linux-2.6.30.5_orig//drivers/net/gianfar.c linux-2.6.30.5/drivers/net/gianfar.c
--- linux-2.6.30.5_orig//drivers/net/gianfar.c	2009-08-16 23:19:38.000000000 +0200
+++ linux-2.6.30.5/drivers/net/gianfar.c	2009-08-22 10:38:28.000000000 +0200
@@ -1309,6 +1309,7 @@ static int gfar_start_xmit(struct sk_buf
 	u32 bufaddr;
 	unsigned long flags;
 	unsigned int nr_frags, length;
+	u32 tempval;
 
 	base = priv->tx_bd_base;
 
@@ -1385,13 +1386,30 @@ static int gfar_start_xmit(struct sk_buf
 		gfar_tx_checksum(skb, fcb);
 	}
 
-	if (priv->vlgrp && vlan_tx_tag_present(skb)) {
-		if (unlikely(NULL == fcb)) {
-			fcb = gfar_add_fcb(skb);
-			lstatus |= BD_LFLAG(TXBD_TOE);
-		}
+	if (priv->vlgrp) {
+		if (vlan_tx_tag_present(skb)) {
+			if (unlikely(NULL == fcb)) {
+				fcb = gfar_add_fcb(skb);
+				lstatus |= BD_LFLAG(TXBD_TOE);
+			}
+
+			/* Enable VLAN tag insertion for frames from VLAN devices */
+			tempval = gfar_read(&priv->regs->tctrl);
+			if ( !(tempval & TCTRL_VLINS) ) {
+				tempval |= TCTRL_VLINS;
+				gfar_write(&priv->regs->tctrl, tempval);
+			}
 
-		gfar_tx_vlan(skb, fcb);
+			gfar_tx_vlan(skb, fcb);
+		}
+		else {
+			/* Disable VLAN tag insertion for frames that are not from a VLAN device */
+			tempval = gfar_read(&priv->regs->tctrl);
+			if ( tempval & TCTRL_VLINS ) {
+				tempval &= ~TCTRL_VLINS;
+				gfar_write(&priv->regs->tctrl, tempval);
+			}
+		}
 	}
 
 	/* setup the TxBD length and buffer pointer for the first BD */
@@ -1484,23 +1502,11 @@ static void gfar_vlan_rx_register(struct
 	priv->vlgrp = grp;
 
 	if (grp) {
-		/* Enable VLAN tag insertion */
-		tempval = gfar_read(&priv->regs->tctrl);
-		tempval |= TCTRL_VLINS;
-
-		gfar_write(&priv->regs->tctrl, tempval);
-
 		/* Enable VLAN tag extraction */
 		tempval = gfar_read(&priv->regs->rctrl);
-		tempval |= RCTRL_VLEX;
 		tempval |= (RCTRL_VLEX | RCTRL_PRSDEP_INIT);
 		gfar_write(&priv->regs->rctrl, tempval);
 	} else {
-		/* Disable VLAN tag insertion */
-		tempval = gfar_read(&priv->regs->tctrl);
-		tempval &= ~TCTRL_VLINS;
-		gfar_write(&priv->regs->tctrl, tempval);
-
 		/* Disable VLAN tag extraction */
 		tempval = gfar_read(&priv->regs->rctrl);
 		tempval &= ~RCTRL_VLEX;

Re: gianfar.c: Unwanted VLAN tagging on TX frames

[Andy Fleming]

[-- Attachment #1: Type: text/plain, Size: 3643 bytes --]

On Mon, Aug 24, 2009 at 11:10 AM, Torsten Fleischer <
to-fleischer@t-online.de> wrote:

> Hello everyone,
>
> I have the Freescale's MPC8313erdb eval board and run the latest stable
> linux
> kernel version (linux-2.6.30.5).
>
> After creating a VLAN device (e.g. eth0.2) a VLAN tag is also inserted into
> frames that don't relate to a VLAN device. This is the case for frames that
> are directly sent through a standard ethernet interface (e.g. eth0).
>
> When creating a VLAN device the gianfar driver enables the  hardware
> supported
> VLAN tagging on TX frames. This is done by setting the VLINS bit of the
> TCTRL
> register inside the function gianfar_vlan_rx_register().
> The problem is that every outgoing frame will be tagged.  For frames from
> an
> interface like eth0 the VLN bit of the FCB isn't set. Therefore the eTSEC
> uses
> the content of the Default VLAN control word register (DFVLAN) to tag the
> frame. As long as this register will not be modified after a reset of the
> controller the outgoing frames will be tagged with VID = 0 (priority tagged
> frames).
>
> The following patch solves this problem.
>
> diff -uprN linux-2.6.30.5_orig//drivers/net/gianfar.c
> linux-2.6.30.5/drivers/net/gianfar.c
> --- linux-2.6.30.5_orig//drivers/net/gianfar.c  2009-08-16
> 23:19:38.000000000 +0200
> +++ linux-2.6.30.5/drivers/net/gianfar.c        2009-08-22
> 10:38:28.000000000 +0200
> @@ -1309,6 +1309,7 @@ static int gfar_start_xmit(struct sk_buf
>        u32 bufaddr;
>        unsigned long flags;
>        unsigned int nr_frags, length;
> +       u32 tempval;
>
>        base = priv->tx_bd_base;
>
> @@ -1385,13 +1386,30 @@ static int gfar_start_xmit(struct sk_buf
>                gfar_tx_checksum(skb, fcb);
>        }
>
> -       if (priv->vlgrp && vlan_tx_tag_present(skb)) {
> -               if (unlikely(NULL == fcb)) {
> -                       fcb = gfar_add_fcb(skb);
> -                       lstatus |= BD_LFLAG(TXBD_TOE);
> -               }
> +       if (priv->vlgrp) {
> +               if (vlan_tx_tag_present(skb)) {
> +                       if (unlikely(NULL == fcb)) {
> +                               fcb = gfar_add_fcb(skb);
> +                               lstatus |= BD_LFLAG(TXBD_TOE);
> +                       }
> +
> +                       /* Enable VLAN tag insertion for frames from VLAN
> devices */
> +                       tempval = gfar_read(&priv->regs->tctrl);
> +                       if ( !(tempval & TCTRL_VLINS) ) {
> +                               tempval |= TCTRL_VLINS;
> +                               gfar_write(&priv->regs->tctrl, tempval);
> +                       }
>
> -               gfar_tx_vlan(skb, fcb);
> +                       gfar_tx_vlan(skb, fcb);
> +               }
> +               else {
> +                       /* Disable VLAN tag insertion for frames that are
> not from a VLAN device */
> +                       tempval = gfar_read(&priv->regs->tctrl);
> +                       if ( tempval & TCTRL_VLINS ) {
> +                               tempval &= ~TCTRL_VLINS;
> +                               gfar_write(&priv->regs->tctrl, tempval);
> +                       }
> +               }
>        }



Hmmm....how have you tested this?  This looks like it has a bad race
condition.  The TCTRL register applies to all packets, which means if you
send a packet with VLAN tags, followed by one without, or visa versa,
there's a reasonable chance that the second packet's VLAN tags (or lack
thereof) will take precedence.

Without speaking for the company, I suspect that this is just how the eTSEC
works with VLAN -- all, or nothing.

Andy

[-- Attachment #2: Type: text/html, Size: 4250 bytes --]

Re: gianfar.c: Unwanted VLAN tagging on TX frames

[Torsten Fleischer]

On Tuesday 25 August 2009 at 01:32:18, Andy Fleming wrote:

>
> Hmmm....how have you tested this?  This looks like it has a bad race
> condition.  The TCTRL register applies to all packets, which means if you
> send a packet with VLAN tags, followed by one without, or visa versa,
> there's a reasonable chance that the second packet's VLAN tags (or lack
> thereof) will take precedence.
>
> Without speaking for the company, I suspect that this is just how the eTSEC
> works with VLAN -- all, or nothing.
>
> Andy

Hi Andy,

I have tested it by sending a single ping to a station within the VLAN 
followed by a ping to a station thats not in a VLAN.
OK, thats not really a significant test, because I did not send a VLAN tagged 
frame immediately followed by one without a tag.
You are right, this code can enable/disable VLAN  tagging before the previous 
packet is processed.

Torsten