EHCI: always clear the STS_FLR status bit

This patch (as1544) fixes a problem affecting some EHCI controllers.
They can generate interrupts whenever the STS_FLR status bit is turned
on, even though that bit is masked out in the Interrupt Enable
register.

Since the driver doesn't use STS_FLR anyway, the patch changes the
interrupt routine to clear that bit whenever it is set, rather than
leaving it alone.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-and-tested-by: Tomoya MORINAGA <tomoya.rohm@gmail.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/ehci-hcd.c

@@ -858,8 +858,13 @@ static irqreturn_t ehci_irq (struct usb_hcd *hcd)
 		goto dead;
 	}
 
+	/*
+	 * We don't use STS_FLR, but some controllers don't like it to
+	 * remain on, so mask it out along with the other status bits.
+	 */
+	masked_status = status & (INTR_MASK | STS_FLR);
+
 	/* Shared IRQ? */
-	masked_status = status & INTR_MASK;
 	if (!masked_status || unlikely(ehci->rh_state == EHCI_RH_HALTED)) {
 		spin_unlock(&ehci->lock);
 		return IRQ_NONE;