USB: ohci: port reset paranoia timeout

This limits how long the OHCI port reset loop waits for the hardware
to do its job, if the controller either (a) dies, or (b) can't finish
the reset. Such limits are always a good idea.

Signed-off-by: David Brownell <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/host/ohci-hub.c

···
 	u32	temp;
 	u16	now = ohci_readl(ohci, &ohci->regs->fmnumber);
 	u16	reset_done = now + PORT_RESET_MSEC;
+	int	limit_1 = DIV_ROUND_UP(PORT_RESET_MSEC, PORT_RESET_HW_MSEC);
 
 	/* build a "continuous enough" reset signal, with up to
 	 * 3msec gap between pulses.  scheduler HZ==100 must work;
 	 * this might need to be deadline-scheduled.
 	 */
 	do {
+		int limit_2;
+
 		/* spin until any current reset finishes */
-		for (;;) {
+		limit_2 = PORT_RESET_HW_MSEC * 2;
+		while (--limit_2 >= 0) {
 			temp = ohci_readl (ohci, portstat);
 			/* handle e.g. CardBus eject */
 			if (temp == ~(u32)0)
···
 			if (!(temp & RH_PS_PRS))
 				break;
 			udelay (500);
+		}
+
+		/* timeout (a hardware error) has been observed when
+		 * EHCI sets CF while this driver is resetting a port;
+		 * presumably other disconnect paths might do it too.
+		 */
+		if (limit_2 < 0) {
+			ohci_dbg(ohci,
+				"port[%d] reset timeout, stat %08x\n",
+				port, temp);
+			break;
 		}
 
 		if (!(temp & RH_PS_CCS))
···
 		ohci_writel (ohci, RH_PS_PRS, portstat);
 		msleep(PORT_RESET_HW_MSEC);
 		now = ohci_readl(ohci, &ohci->regs->fmnumber);
-	} while (tick_before(now, reset_done));
-	/* caller synchronizes using PRSC */
+	} while (tick_before(now, reset_done) && --limit_1 >= 0);
+
+	/* caller synchronizes using PRSC ... and handles PRS
+	 * still being set when this returns.
+	 */
 
 	return 0;
 }