phy: fix crash in fixed_phy_add()

Since e7f4dc3536 ("mdio: Move allocation of interrupts into core"),
platforms which call fixed_phy_add() before fixed_mdio_bus_init() is
called (for example, because the platform code and the fixed_phy driver
use the same initcall level) crash in fixed_phy_add() since the
->mii_bus is not allocated.

Also since e7f4dc3536, these interrupts are initalized to polling by
default.  The few (old) platforms which directly use fixed_phy_add()
from their platform code all pass PHY_POLL for the irq argument, so we
can keep these platforms not crashing by simply not attempting to set
the irq if PHY_POLL is passed.

Also, even if problems have not been reported on more modern platforms
which used fixed_phy_register() from drivers' probe functions, we return
-EPROBE_DEFER if the MDIO bus is not yet registered so that the probe is
retried later.

Fixes: e7f4dc3536 ("mdio: Move allocation of interrupts into core")
Signed-off-by: Rabin Vincent <rabinv@axis.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/fixed_phy.c

@@ -255,7 +255,8 @@ int fixed_phy_add(unsigned int irq, int phy_addr,
 
 	memset(fp->regs, 0xFF,  sizeof(fp->regs[0]) * MII_REGS_NUM);
 
-	fmb->mii_bus->irq[phy_addr] = irq;
+	if (irq != PHY_POLL)
+		fmb->mii_bus->irq[phy_addr] = irq;
 
 	fp->addr = phy_addr;
 	fp->status = *status;
@@ -314,6 +315,9 @@ struct phy_device *fixed_phy_register(unsigned int irq,
 	int phy_addr;
 	int ret;
 
+	if (!fmb->mii_bus || fmb->mii_bus->state != MDIOBUS_REGISTERED)
+		return ERR_PTR(-EPROBE_DEFER);
+
 	/* Get the next available PHY address, up to PHY_MAX_ADDR */
 	spin_lock(&phy_fixed_addr_lock);
 	if (phy_fixed_addr == PHY_MAX_ADDR) {