usb: dwc3: Allow usb role swich control from userspace

There is a possibility of user needs for USB mode switching on boards
that lack external hardware support for dynamic host/device role
detection. This is particularly relevant in automotive applications
where userspace applications need to switch USB roles (host to device)
at runtime for CarPlay/Android Auto integration.

Add an `allow_userspace_control` flag to handle such cases. When
enabled, it exposes a sysfs attribute that allows userspace to switch
the USB role manually between host and device. This provides flexibility
for platforms that cannot rely on hardware-based mode detection.

The role switch can be done as below
echo host > /sys/class/usb_role/<ADDR>.usb-role-switch/role
echo device > /sys/class/usb_role/<ADDR>.usb-role-switch/role

Acked-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Signed-off-by: Pritam Manohar Sutar <pritam.sutar@samsung.com>
Link: https://patch.msgid.link/20251024085455.789555-1-pritam.sutar@samsung.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: pritamsutar

drivers/usb/dwc3/drd.c

@@ -515,6 +515,7 @@ static int dwc3_setup_role_switch(struct dwc3 *dwc)
 	dwc3_role_switch.set = dwc3_usb_role_switch_set;
 	dwc3_role_switch.get = dwc3_usb_role_switch_get;
 	dwc3_role_switch.driver_data = dwc;
+	dwc3_role_switch.allow_userspace_control = true;
 	dwc->role_sw = usb_role_switch_register(dwc->dev, &dwc3_role_switch);
 	if (IS_ERR(dwc->role_sw))
 		return PTR_ERR(dwc->role_sw);