gianfar: Enable eTSEC-20 erratum w/a for P2020 Rev1

Enable workaround for P2020/P2010 erratum eTSEC 20,
"Excess delays when transmitting TOE=1 large frames".
The impact is that frames lager than 2500-bytes for which
TOE (i.e. TCP/IP hw accelerations like Tx csum) is enabled
may see excess delay before start of transmission.
This erratum was fixed in Rev 2.0.
Signed-off-by: NClaudiu Manoil <claudiu.manoil@freescale.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/gianfar.c

@@ -968,6 +968,9 @@ static void __gfar_detect_errata_85xx(struct gfar_private *priv)
 
 	if ((SVR_SOC_VER(svr) == SVR_8548) && (SVR_REV(svr) == 0x20))
 		priv->errata |= GFAR_ERRATA_12;
+	if (((SVR_SOC_VER(svr) == SVR_P2020) && (SVR_REV(svr) < 0x20)) ||
+	    ((SVR_SOC_VER(svr) == SVR_P2010) && (SVR_REV(svr) < 0x20)))
+		priv->errata |= GFAR_ERRATA_76; /* aka eTSEC 20 */
 }
 
 static void gfar_detect_errata(struct gfar_private *priv)