net: phy: avoid clearing PHY interrupts twice in irq handler

On all PHY drivers that implement did_interrupt() reading the interrupt
status bits clears them. This means we may loose an interrupt that
is triggered between calling did_interrupt() and phy_clear_interrupt().
As part of the fix make it a requirement that did_interrupt() clears
the interrupt.

The Fixes tag refers to the first commit where the patch applies
cleanly.

Fixes: 49644e68 ("net: phy: add callback for custom interrupt handler to struct phy_driver")
Reported-by: NMichael Walle <michael@walle.cc>
Signed-off-by: NHeiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/phy/phy.c

@@ -727,7 +727,8 @@ static irqreturn_t phy_interrupt(int irq, void *phy_dat)
 		phy_trigger_machine(phydev);
 	}
 
-	if (phy_clear_interrupt(phydev))
+	/* did_interrupt() may have cleared the interrupt already */
+	if (!phydev->drv->did_interrupt && phy_clear_interrupt(phydev))
 		goto phy_err;
 	return IRQ_HANDLED;
 

include/linux/phy.h

@@ -557,6 +557,7 @@ struct phy_driver {
 	/*
 	 * Checks if the PHY generated an interrupt.
 	 * For multi-PHY devices with shared PHY interrupt pin
+	 * Set interrupt bits have to be cleared.
 	 */
 	int (*did_interrupt)(struct phy_device *phydev);