Patchwork gianfar: Fall back to software tcp/udp checksum on older controllers

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Submitter Alex Dubov
Date Jan. 27, 2011, 8:14 a.m.
Message ID <468529.34173.qm@web37605.mail.mud.yahoo.com>
Download mbox | patch
Permalink /patch/80607/
State Not Applicable
Headers show

Comments

Alex Dubov - Jan. 27, 2011, 8:14 a.m.
As specified by errata eTSEC49 of MPC8548 and errata eTSEC12 of MPC83xx,
older revisions of gianfar controllers will be unable to calculate a TCP/UDP
packet checksum for some aligments of the appropriate FCB. This patch checks
for FCB alignment on such controllers and falls back to software checksumming
if the aligment is known to be bad.

Signed-off-by: Alex Dubov <oakad@yahoo.com>
---
This is my, somewhat different approach to Matthew Creech proposed solution.

 drivers/net/gianfar.c |   21 +++++++++++++++++++--
 drivers/net/gianfar.h |    1 +
 2 files changed, 20 insertions(+), 2 deletions(-)
Anton Vorontsov - Jan. 27, 2011, 9:51 a.m.
Hello Alex,

On Thu, Jan 27, 2011 at 12:14:21AM -0800, Alex Dubov wrote:
> As specified by errata eTSEC49 of MPC8548 and errata eTSEC12 of MPC83xx,
> older revisions of gianfar controllers will be unable to calculate a TCP/UDP
> packet checksum for some aligments of the appropriate FCB. This patch checks
> for FCB alignment on such controllers and falls back to software checksumming
> if the aligment is known to be bad.
> 
> Signed-off-by: Alex Dubov <oakad@yahoo.com>
> ---
> This is my, somewhat different approach to Matthew Creech proposed solution.
> 
>  drivers/net/gianfar.c |   21 +++++++++++++++++++--
>  drivers/net/gianfar.h |    1 +
>  2 files changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/gianfar.c b/drivers/net/gianfar.c
> index 5ed8f9f..b4f0e99 100644
> --- a/drivers/net/gianfar.c
> +++ b/drivers/net/gianfar.c
> @@ -950,6 +950,11 @@ static void gfar_detect_errata(struct gfar_private *priv)
>  			(pvr == 0x80861010 && (mod & 0xfff9) == 0x80c0))
>  		priv->errata |= GFAR_ERRATA_A002;
>  
> +	/* MPC8313 Rev < 2.0, MPC8548 rev 2.0 */
> +	if ((pvr == 0x80850010 && mod == 0x80b0 && rev < 0x0020)
> +	    || (pvr == 0x80210020 && mod == 0x8030 && rev == 0x0020))

Please indent it like the above: with two tabs. This is
to keep things consistent.

> +		priv->errata |= GFAR_ERRATA_12;
> +
>  	if (priv->errata)
>  		dev_info(dev, "enabled errata workarounds, flags: 0x%x\n",
>  			 priv->errata);
> @@ -2156,8 +2161,20 @@ static int gfar_start_xmit(struct sk_buff *skb, struct net_device *dev)
>  	/* Set up checksumming */
>  	if (CHECKSUM_PARTIAL == skb->ip_summed) {
>  		fcb = gfar_add_fcb(skb);
> -		lstatus |= BD_LFLAG(TXBD_TOE);
> -		gfar_tx_checksum(skb, fcb);
> +		switch (unlikely(gfar_has_errata(priv, GFAR_ERRATA_12))
> +			? 1 : 0) {

The switch construction is quite bizarre. ;-) Why not

if (gfar_has_errata() && (ulong)fcb % 0x20 > 18) {
	csum_help();
} else {
	lstatus |=...
	tx_csum();
}

?

Thanks,

> +		case 1:
> +			/* as specified by errata */
> +			if (((unsigned long)fcb % 0x20) > 0x18) { 
> +				__skb_pull(skb, GMAC_FCB_LEN);
> +				skb_checksum_help(skb);
> +				break;
> +			}
> +			/* otherwise, fall through */
> +		default:
> +			lstatus |= BD_LFLAG(TXBD_TOE);
> +			gfar_tx_checksum(skb, fcb);
> +		}
>  	}
David Miller - Jan. 27, 2011, 10:23 p.m.
Please CC: netdev on future submissions of this patch, otherwise I
won't see it in my queue.
Alex Dubov - Jan. 28, 2011, 2:43 a.m.
> > -       
> gfar_tx_checksum(skb, fcb);
> > +        switch
> (unlikely(gfar_has_errata(priv, GFAR_ERRATA_12))
> > +       
>     ? 1 : 0) {
> 
> The switch construction is quite bizarre. ;-) Why not
> 

My testing shows that even on broken chips unaligned packets are quite rare
(only some SYN packets seem to be affected). So I tried to leave the
checksum offload path as the most preferred one.

Patch

diff --git a/drivers/net/gianfar.c b/drivers/net/gianfar.c
index 5ed8f9f..b4f0e99 100644
--- a/drivers/net/gianfar.c
+++ b/drivers/net/gianfar.c
@@ -950,6 +950,11 @@  static void gfar_detect_errata(struct gfar_private *priv)
 			(pvr == 0x80861010 && (mod & 0xfff9) == 0x80c0))
 		priv->errata |= GFAR_ERRATA_A002;
 
+	/* MPC8313 Rev < 2.0, MPC8548 rev 2.0 */
+	if ((pvr == 0x80850010 && mod == 0x80b0 && rev < 0x0020)
+	    || (pvr == 0x80210020 && mod == 0x8030 && rev == 0x0020))
+		priv->errata |= GFAR_ERRATA_12;
+
 	if (priv->errata)
 		dev_info(dev, "enabled errata workarounds, flags: 0x%x\n",
 			 priv->errata);
@@ -2156,8 +2161,20 @@  static int gfar_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	/* Set up checksumming */
 	if (CHECKSUM_PARTIAL == skb->ip_summed) {
 		fcb = gfar_add_fcb(skb);
-		lstatus |= BD_LFLAG(TXBD_TOE);
-		gfar_tx_checksum(skb, fcb);
+		switch (unlikely(gfar_has_errata(priv, GFAR_ERRATA_12))
+			? 1 : 0) {
+		case 1:
+			/* as specified by errata */
+			if (((unsigned long)fcb % 0x20) > 0x18) { 
+				__skb_pull(skb, GMAC_FCB_LEN);
+				skb_checksum_help(skb);
+				break;
+			}
+			/* otherwise, fall through */
+		default:
+			lstatus |= BD_LFLAG(TXBD_TOE);
+			gfar_tx_checksum(skb, fcb);
+		}
 	}
 
 	if (vlan_tx_tag_present(skb)) {
diff --git a/drivers/net/gianfar.h b/drivers/net/gianfar.h
index 54de413..ec5d595 100644
--- a/drivers/net/gianfar.h
+++ b/drivers/net/gianfar.h
@@ -1039,6 +1039,7 @@  enum gfar_errata {
 	GFAR_ERRATA_74		= 0x01,
 	GFAR_ERRATA_76		= 0x02,
 	GFAR_ERRATA_A002	= 0x04,
+	GFAR_ERRATA_12		= 0x08, /* a.k.a errata eTSEC49 */
 };
 
 /* Struct stolen almost completely (and shamelessly) from the FCC enet source