tg3: Improve PCI function number detection.

Simplify the code to detect PCI function number on 5717, 5719, and 5720.
If shared memory does not have proper signature, read the function number
from register directly.
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/tg3.c

@@ -15441,22 +15441,19 @@ static int tg3_get_invariants(struct tg3 *tp, const struct pci_device_id *ent)
 					      &val);
 			tp->pci_fn = val & 0x7;
 		}
-	} else if (GET_ASIC_REV(tp->pci_chip_rev_id) == ASIC_REV_5717) {
-		tg3_read_mem(tp, NIC_SRAM_CPMU_STATUS, &val);
-		if ((val & NIC_SRAM_CPMUSTAT_SIG_MSK) ==
-		    NIC_SRAM_CPMUSTAT_SIG) {
-			tp->pci_fn = val & TG3_CPMU_STATUS_FMSK_5717;
-			tp->pci_fn = tp->pci_fn ? 1 : 0;
-		}
-	} else if (GET_ASIC_REV(tp->pci_chip_rev_id) == ASIC_REV_5719 ||
+	} else if (GET_ASIC_REV(tp->pci_chip_rev_id) == ASIC_REV_5717 ||
+		   GET_ASIC_REV(tp->pci_chip_rev_id) == ASIC_REV_5719 ||
 		   GET_ASIC_REV(tp->pci_chip_rev_id) == ASIC_REV_5720) {
 		tg3_read_mem(tp, NIC_SRAM_CPMU_STATUS, &val);
-		if ((val & NIC_SRAM_CPMUSTAT_SIG_MSK) ==
-		    NIC_SRAM_CPMUSTAT_SIG) {
+		if ((val & NIC_SRAM_CPMUSTAT_SIG_MSK) != NIC_SRAM_CPMUSTAT_SIG)
+			val = tr32(TG3_CPMU_STATUS);
+
+		if (GET_ASIC_REV(tp->pci_chip_rev_id) == ASIC_REV_5717)
+			tp->pci_fn = (val & TG3_CPMU_STATUS_FMSK_5717) ? 1 : 0;
+		else
 			tp->pci_fn = (val & TG3_CPMU_STATUS_FMSK_5719) >>
 				     TG3_CPMU_STATUS_FSHFT_5719;
 	}
-	}
 
 	/* Get eeprom hw config before calling tg3_set_power_state().
 	 * In particular, the TG3_FLAG_IS_NIC flag must be