b44: abort when no PHY is available at all

When the phy address is 31, this means that there is no PHY connected
to this MAC at all, no internal and no external PHY. Reading these PHY
registers causes a system reset on some routers.
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/b44.c

@@ -2206,6 +2206,12 @@ static int b44_init_one(struct ssb_device *sdev,
 		goto err_out_powerdown;
 	}
 
+	if (bp->phy_addr == B44_PHY_ADDR_NO_PHY) {
+		dev_err(sdev->dev, "No PHY present on this MAC, aborting\n");
+		err = -ENODEV;
+		goto err_out_powerdown;
+	}
+
 	bp->mii_if.dev = dev;
 	bp->mii_if.mdio_read = b44_mii_read;
 	bp->mii_if.mdio_write = b44_mii_write;

drivers/net/ethernet/broadcom/b44.h

@@ -282,6 +282,7 @@ struct ring_info {
 
 #define B44_MCAST_TABLE_SIZE		32
 #define B44_PHY_ADDR_NO_LOCAL_PHY	30 /* no local phy regs */
+#define B44_PHY_ADDR_NO_PHY		31 /* no phy present at all */
 #define B44_MDC_RATIO			5000000
 
 #define	B44_STAT_REG_DECLARE		\