xhci: Add grace period after xHC start to prevent premature runtime suspend.

After xHC controller is started, either in probe or resume, it can take
a while before any of the connected usb devices are visible to the roothub
due to link training.

It's possible xhci driver loads, sees no acivity and suspends the host
before the USB device is visible.

In one testcase with a hotplugged xHC controller the host finally detected
the connected USB device and generated a wake 500ms after host initial
start.

If hosts didn't suspend the device duringe training it probablty wouldn't
take up to 500ms to detect it, but looking at specs reveal USB3 link
training has a couple long timeout values, such as 120ms
RxDetectQuietTimeout, and 360ms PollingLFPSTimeout.

So Add a 500ms grace period that keeps polling the roothub for 500ms after
start, preventing runtime suspend until USB devices are detected.

Cc: [e-mail]
Signed-off-by: Mathias Nyman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/host/xhci-hub.c

···
 
 	status = bus_state->resuming_ports;
 
+	/*
+	 * SS devices are only visible to roothub after link training completes.
+	 * Keep polling roothubs for a grace period after xHC start
+	 */
+	if (xhci->run_graceperiod) {
+		if (time_before(jiffies, xhci->run_graceperiod))
+			status = 1;
+		else
+			xhci->run_graceperiod = 0;
+	}
+
 	mask = PORT_CSC | PORT_PEC | PORT_OCC | PORT_PLC | PORT_WRC | PORT_CEC;
 
 	/* For each port, did anything change?  If so, set that bit in buf. */

drivers/usb/host/xhci.c

···
 		xhci_err(xhci, "Host took too long to start, "
 				"waited %u microseconds.\n",
 				XHCI_MAX_HALT_USEC);
-	if (!ret)
+	if (!ret) {
 		/* clear state flags. Including dying, halted or removing */
 		xhci->xhc_state = 0;
+		xhci->run_graceperiod = jiffies + msecs_to_jiffies(500);
+	}
 
 	return ret;
 }

drivers/usb/host/xhci.h

···
 
 	/* Host controller watchdog timer structures */
 	unsigned int		xhc_state;
-
+	unsigned long		run_graceperiod;
 	u32			command;
 	struct s3_save		s3;
 /* Host controller is dying - not responding to commands. "I'm not dead yet!"