usb_charger: disconnect usb switch until connection is debounced

Re-order logic in BC1.2 detection task so that we open the
USB switches immediately upon detecting a connection, then
debounce the connection, then reset the pericom and determine
BC1.2 charger type.

This fixes two problems:
- Problem where host could enumerate dut, detect disconnect,
and then re-enumerate.
- Problem where sometimes dut would detect a host workstation
as a proprietary charger because we weren't delaying long
enough after opening USB switches before triggering pericom
reset.

BUG=chrome-os-partner:47219
BRANCH=smaug
TEST=tested by connecting workstation to ryu (tested both
pluggin in A side first and C side first). Without this patch,
my workstation often see's disconnect and reconnect. With
this change we only get one connect.

Change-Id: I07cc3473ff32953fad3cc6d1db01b86b44969c4e
Signed-off-by: Alec Berg <alecaberg@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/311804
Reviewed-by: Shawn N <shawnn@chromium.org>

common/usb_charger.c

@@ -113,15 +113,18 @@ static void usb_charger_bc12_detect(int port)
 
 	/* Debounce pin plug order if we detect a charger */
 	if (device_type || PI3USB9281_CHG_STATUS_ANY(charger_status)) {
-		msleep(USB_CHG_DEBOUNCE_DELAY_MS);
-
 		/* next operation might trigger a detach interrupt */
 		pi3usb9281_disable_interrupts(port);
-		/* Ensure D+/D- are open before resetting */
+		/*
+		 * Ensure D+/D- are open before resetting
+		 * Note: we can't simply call pi3usb9281_set_switches() because
+		 * another task might override it and set the switches closed.
+		 */
 		pi3usb9281_set_switch_manual(port, 1);
 		pi3usb9281_set_pins(port, 0);
-		/* Let D+/D- relax to their idle state */
-		msleep(40);
+
+		/* Delay to debounce pin attach order */
+		msleep(USB_CHG_DEBOUNCE_DELAY_MS);
 
 		/*
 		 * Trigger chip reset to refresh detection registers.