Gianfar TCP checksumming broken in 2.6.35+

[Matthew L. Creech]

On Thu, Nov 18, 2010 at 12:06 PM, David Miller <davem at davemloft.net> wrote:
>
> Can someone please follow up Matthew to get this bug resolved?  It has
> been sitting around for a long time.
>
> I suspect the gianfar driver, for these chip revisions, will need to
> do a software checksum when the offset matches the criteria mentioned
> in the errata above.
>

I added a patch for this which fixes our affected systems; however, I
don't know if this is a good way to perform checksum offloading, I
just kind of dug around until I found a function that seemed like it
worked.  :)  Patch against 2.6.36 is below for reference.


---
 gianfar.c |   21 +++++++++++++++++++--
 gianfar.h |    1 +
 2 files changed, 20 insertions(+), 2 deletions(-)

diff -purN orig/drivers/net/gianfar.c linux-2.6.36/drivers/net/gianfar.c
--- orig/drivers/net/gianfar.c	2010-11-03 15:10:29.287140651 -0400
+++ linux-2.6.36/drivers/net/gianfar.c	2010-11-03 16:01:03.754321896 -0400
@@ -937,6 +937,10 @@ static void gfar_detect_errata(struct gf
 	unsigned int mod = (svr >> 16) & 0xfff6; /* w/o E suffix */
 	unsigned int rev = svr & 0xffff;

+	/* MPC8313 Rev < 2.0 */
+	if (pvr == 0x80850010 && mod == 0x80b0 && rev < 0x0020)
+		priv->errata |= GFAR_ERRATA_12;
+
 	/* MPC8313 Rev 2.0 and higher; All MPC837x */
 	if ((pvr == 0x80850010 && mod == 0x80b0 && rev >= 0x0020) ||
 			(pvr == 0x80861010 && (mod & 0xfff9) == 0x80c0))
@@ -1984,7 +1988,8 @@ static inline struct txfcb *gfar_add_fcb
 	return fcb;
 }

-static inline void gfar_tx_checksum(struct sk_buff *skb, struct txfcb *fcb)
+static inline void gfar_tx_checksum(struct sk_buff *skb, struct txfcb *fcb,
+				int has_csum_bug)
 {
 	u8 flags = 0;

@@ -1994,6 +1999,17 @@ static inline void gfar_tx_checksum(stru
 	 */
 	flags = TXFCB_DEFAULT;

+	/* If using old-rev silicon, the alignment of the TXFCB may be off,
+	 * causing TCP checksumming to fail (errata eTSEC12).  In that case,
+	 * we compute the checksum manually.
+	 */
+	if (has_csum_bug) {
+		/* Disable handling of TCP/UDP header (checksumming) */
+		flags &= ~TXFCB_TUP;
+		/* Manually add checksum */
+		skb_checksum_help(skb);
+	}
+
 	/* Tell the controller what the protocol is */
 	/* And provide the already calculated phcs */
 	if (ip_hdr(skb)->protocol == IPPROTO_UDP) {
@@ -2159,7 +2175,8 @@ static int gfar_start_xmit(struct sk_buf
 	if (CHECKSUM_PARTIAL == skb->ip_summed) {
 		fcb = gfar_add_fcb(skb);
 		lstatus |= BD_LFLAG(TXBD_TOE);
-		gfar_tx_checksum(skb, fcb);
+		gfar_tx_checksum(skb, fcb,
+				gfar_has_errata(priv, GFAR_ERRATA_12));
 	}

 	if (priv->vlgrp && vlan_tx_tag_present(skb)) {
diff -purN orig/drivers/net/gianfar.h linux-2.6.36/drivers/net/gianfar.h
--- orig/drivers/net/gianfar.h	2010-11-03 15:10:29.257142194 -0400
+++ linux-2.6.36/drivers/net/gianfar.h	2010-11-03 15:48:10.117134959 -0400
@@ -1029,6 +1029,7 @@ enum gfar_errata {
 	GFAR_ERRATA_74		= 0x01,
 	GFAR_ERRATA_76		= 0x02,
 	GFAR_ERRATA_A002	= 0x04,
+	GFAR_ERRATA_12		= 0x08,
 };

 /* Struct stolen almost completely (and shamelessly) from the FCC enet source

-- 
Matthew L. Creech