tg3: Add workaround to restrict 5762 MRRS to 2048

One of AMD based server with 5762 hangs with jumbo frame traffic.
This AMD platform has southbridge limitation which is restricting MRRS
to 4000. As a work around, driver to restricts the MRRS to 2048 for
this particular 5762 NX1 card.
Signed-off-by: Siva Reddy Kallam <siva.kallam@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/tg3.c

@@ -10054,6 +10054,16 @@ static int tg3_reset_hw(struct tg3 *tp, bool reset_phy)
 
 	tw32(GRC_MODE, tp->grc_mode | val);
 
+	/* On one of the AMD platform, MRRS is restricted to 4000 because of
+	 * south bridge limitation. As a workaround, Driver is setting MRRS
+	 * to 2048 instead of default 4096.
+	 */
+	if (tp->pdev->subsystem_vendor == PCI_VENDOR_ID_DELL &&
+	    tp->pdev->subsystem_device == TG3PCI_SUBDEVICE_ID_DELL_5762) {
+		val = tr32(TG3PCI_DEV_STATUS_CTRL) & ~MAX_READ_REQ_MASK;
+		tw32(TG3PCI_DEV_STATUS_CTRL, val | MAX_READ_REQ_SIZE_2048);
+	}
+
 	/* Setup the timer prescalar register.  Clock is always 66Mhz. */
 	val = tr32(GRC_MISC_CFG);
 	val &= ~0xff;

drivers/net/ethernet/broadcom/tg3.h

@@ -97,6 +97,7 @@
 #define TG3PCI_SUBDEVICE_ID_DELL_JAGUAR		0x0106
 #define TG3PCI_SUBDEVICE_ID_DELL_MERLOT		0x0109
 #define TG3PCI_SUBDEVICE_ID_DELL_SLIM_MERLOT	0x010a
+#define TG3PCI_SUBDEVICE_ID_DELL_5762		0x07f0
 #define TG3PCI_SUBVENDOR_ID_COMPAQ		PCI_VENDOR_ID_COMPAQ
 #define TG3PCI_SUBDEVICE_ID_COMPAQ_BANSHEE	0x007c
 #define TG3PCI_SUBDEVICE_ID_COMPAQ_BANSHEE_2	0x009a
@@ -282,6 +283,9 @@
 #define TG3PCI_STD_RING_PROD_IDX	0x00000098 /* 64-bit */
 #define TG3PCI_RCV_RET_RING_CON_IDX	0x000000a0 /* 64-bit */
 /* 0xa8 --> 0xb8 unused */
+#define TG3PCI_DEV_STATUS_CTRL		0x000000b4
+#define  MAX_READ_REQ_SIZE_2048		 0x00004000
+#define  MAX_READ_REQ_MASK		 0x00007000
 #define TG3PCI_DUAL_MAC_CTRL		0x000000b8
 #define  DUAL_MAC_CTRL_CH_MASK		 0x00000003
 #define  DUAL_MAC_CTRL_ID		 0x00000004