USB: chipidea: Do not hang when CONFIG_USB_CHIPIDEA_ULPI is not selected

From: Fabio Estevam <redacted>

Since commit 03e6275ae381087bd8 ("usb: chipidea: Fix ULPI on imx51") the
kernel hangs on a imx51-babbage board, when using the ULPI interface with
the CONFIG_USB_CHIPIDEA_ULPI option unselected.

Instead of hanging the kernel, let's warn the user that
CONFIG_USB_CHIPIDEA_ULPI needs to be selected, propagate an error
and continue with booting the kernel.

The user can then react to the warning and select
CONFIG_USB_CHIPIDEA_ULPI as needed.

Fixes: 03e6275ae381087bd8 ("usb: chipidea: Fix ULPI on imx51")
Suggested-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Fabio Estevam <redacted>
---
 drivers/usb/chipidea/core.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/usb/chipidea/core.c b/drivers/usb/chipidea/core.c
index 85fc6db..5ab9db1 100644
--- a/drivers/usb/chipidea/core.c
+++ b/drivers/usb/chipidea/core.c

@@ -608,6 +608,16 @@ static int ci_get_platdata(struct device *dev,
 	if (!platdata->phy_mode)
 		platdata->phy_mode = of_usb_get_phy_mode(dev->of_node);
 
+	if (platdata->phy_mode == USBPHY_INTERFACE_MODE_ULPI) {
+		/*
+		 * CONFIG_USB_CHIPIDEA_ULPI needs to be selected
+		 * for proper usage of the ULPI mode
+		 */
+		WARN_ONCE(!IS_ENABLED(CONFIG_USB_CHIPIDEA_ULPI),
+		"Select CONFIG_USB_CHIPIDEA_ULPI in order to use ULPI mode\n");
+		return -EINVAL;
+	}
+
 	if (!platdata->dr_mode)
 		platdata->dr_mode = usb_get_dr_mode(dev);