libpayload: drivers/usb: add a USB pre-poll hook

This adds a hook so that a payload can optionally perform USB service
functions in conjunction with regular USB port status polling. In
particular, this allows depthcharge to control the state of an
external USB mux. Some SoCs like Tiger Lake have a USB mux for Type-C
ports that must be kept in sync with the state of the port as reported
by the TCPC. This can be achieved by hooking into the poll routine to
refresh the state of the USB mux.

BUG=b:149883933
TEST=booted into recovery from Type-C flash drive on volteer

Change-Id: Ic6c23756f64b891b3c5683cd650c605b8630b0fb
Signed-off-by: Caveh Jalali <caveh@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/42072
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

payloads/libpayload/drivers/usb/usb.c

@@ -86,6 +86,10 @@ usb_poll (void)
 {
 	if (usb_hcs == 0)
 		return;
+
+	if (usb_poll_prepare)
+		usb_poll_prepare();
+
 	hci_t *controller = usb_hcs;
 	while (controller != NULL) {
 		int i;

payloads/libpayload/include/usb/usb.h

@@ -344,6 +344,13 @@ static inline void usb_debug(const char *fmt, ...)
 #endif
 }
 
+/**
+ * To be implemented by libpayload-client. It's called by the USB
+ * stack just before iterating over known devices to poll them for
+ * status change.
+ */
+void __attribute__((weak)) usb_poll_prepare (void);
+
 /**
  * To be implemented by libpayload-client. It's called by the USB stack
  * when a new USB device is found which isn't claimed by a built in driver,