usb: xhci-dwc3: Support role switch default role

When the device tree indicates support for role switching through
the "usb-role-switch" property, take the "role-switch-default-mode"
property into account when deciding which role to put the
controller into.

This makes USB devices work on Apple M1 systems where the device
tree may include a "dr_mode" property that is set to "otg", but
where we need to put the controller into "host" mode to see
devices connected to the type-C ports.

Signed-off-by: Mark Kettenis <kettenis@openbsd.org>
diff --git a/drivers/usb/common/common.c b/drivers/usb/common/common.c
index ee0c064..cff86a5 100644
--- a/drivers/usb/common/common.c
+++ b/drivers/usb/common/common.c
@@ -40,6 +40,22 @@
 	return USB_DR_MODE_UNKNOWN;
 }
 
+enum usb_dr_mode usb_get_role_switch_default_mode(ofnode node)
+{
+	const char *dr_mode;
+	int i;
+
+	dr_mode = ofnode_read_string(node, "role-switch-default-mode");
+	if (!dr_mode)
+		return USB_DR_MODE_UNKNOWN;
+
+	for (i = 0; i < ARRAY_SIZE(usb_dr_modes); i++)
+		if (!strcmp(dr_mode, usb_dr_modes[i]))
+			return i;
+
+	return USB_DR_MODE_UNKNOWN;
+}
+
 static const char *const speed_names[] = {
 	[USB_SPEED_UNKNOWN] = "UNKNOWN",
 	[USB_SPEED_LOW] = "low-speed",