Subject: [PATCH] gianfar: Fall back to software tcp/udp checksum on older controllers

From: Alex Dubov <[email-masked]>
Date: Thu, 27 Jan 2011 00:14:21 -0800 (PST)

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 <[email-masked]>
---
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))
+		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
-- 
1.7.3.2