[PATCH v2 1/2] usb: dwc3-generic: allow fallback of dr_mode property to "otg"

[Kaustabh Chakraborty]

Documentation [1] states that the default value of the dr_mode property
is "otg". It also isn't marked a mandatory node, so it may or may not be
set. So, accordingly if dr_mode is not mentioned in the devicetree node,
OTG mode must be assumed.

In this driver however, this case is not handled. If dr_mode is not
mentioned, USB_DR_MODE_UNKNOWN is set. The logic implemented raises an
error, instead of falling back to USB_DR_MODE_OTG. Correct this to
conform to the specification.

Link: https://elixir.bootlin.com/u-boot/v2025.10/source/dts/upstream/Bindings/usb/usb-drd.yaml#L23 [1]
Signed-off-by: Kaustabh Chakraborty <kauschluss at disroot.org>
---
 drivers/usb/dwc3/dwc3-generic.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/dwc3/dwc3-generic.c b/drivers/usb/dwc3/dwc3-generic.c
index c09014aec60..1967594f48a 100644
--- a/drivers/usb/dwc3/dwc3-generic.c
+++ b/drivers/usb/dwc3/dwc3-generic.c
@@ -173,8 +173,8 @@ static int dwc3_generic_of_to_plat(struct udevice *dev)
 		node = dev_ofnode(dev->parent);
 		plat->dr_mode = usb_get_dr_mode(node);
 		if (plat->dr_mode == USB_DR_MODE_UNKNOWN) {
-			pr_err("Invalid usb mode setup\n");
-			return -ENODEV;
+			pr_info("No USB mode specified. Using 'otg'\n");
+			plat->dr_mode = USB_DR_MODE_OTG;
 		}
 	}
 
@@ -516,6 +516,10 @@ static int dwc3_glue_bind_common(struct udevice *parent, ofnode node)
 	if (!dr_mode)
 		dr_mode = usb_get_dr_mode(node);
 
+	/* usb mode must fallback to peripheral if not known */
+	if (dr_mode == USB_DR_MODE_UNKNOWN)
+		dr_mode = USB_DR_MODE_OTG;
+
 	if (CONFIG_IS_ENABLED(DM_USB_GADGET) &&
 	    (dr_mode == USB_DR_MODE_PERIPHERAL || dr_mode == USB_DR_MODE_OTG)) {
 		debug("%s: dr_mode: OTG or Peripheral\n", __func__);

-- 
2.52.0