tg3: Skip powering down function 0 on certain serdes devices

On the 5718, 5719 and 5720 serdes devices, powering down function 0
results in all the other ports being powered down. Add code to skip
function 0 power down.

v2:
 - Modify tg3_phy_power_bug() function to use a switch instead of a
   complicated if statement. Suggested by Joe Perches.

Cc: <stable@vger.kernel.org>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: Nithin Nayak Sujir <nsujir@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/tg3.c

@@ -2957,6 +2957,31 @@ static int tg3_5700_link_polarity(struct tg3 *tp, u32 speed)
 	return 0;
 }
 
+static bool tg3_phy_power_bug(struct tg3 *tp)
+{
+	switch (tg3_asic_rev(tp)) {
+	case ASIC_REV_5700:
+	case ASIC_REV_5704:
+		return true;
+	case ASIC_REV_5780:
+		if (tp->phy_flags & TG3_PHYFLG_MII_SERDES)
+			return true;
+		return false;
+	case ASIC_REV_5717:
+		if (!tp->pci_fn)
+			return true;
+		return false;
+	case ASIC_REV_5719:
+	case ASIC_REV_5720:
+		if ((tp->phy_flags & TG3_PHYFLG_PHY_SERDES) &&
+		    !tp->pci_fn)
+			return true;
+		return false;
+	}
+
+	return false;
+}
+
 static void tg3_power_down_phy(struct tg3 *tp, bool do_low_power)
 {
 	u32 val;
@@ -3016,12 +3041,7 @@ static void tg3_power_down_phy(struct tg3 *tp, bool do_low_power)
 	/* The PHY should not be powered down on some chips because
 	 * of bugs.
 	 */
-	if (tg3_asic_rev(tp) == ASIC_REV_5700 ||
-	    tg3_asic_rev(tp) == ASIC_REV_5704 ||
-	    (tg3_asic_rev(tp) == ASIC_REV_5780 &&
-	     (tp->phy_flags & TG3_PHYFLG_MII_SERDES)) ||
-	    (tg3_asic_rev(tp) == ASIC_REV_5717 &&
-	     !tp->pci_fn))
+	if (tg3_phy_power_bug(tp))
 		return;
 
 	if (tg3_chip_rev(tp) == CHIPREV_5784_AX ||