Re: [PATCH v3 1/2] usb: dwc3-generic: allow fallback of dr_mode property to "otg"

[Mattijs Korpershoek <mkorpershoek@kernel.org>]

Hi Kaustabh,

Thank you for the patch.

On Thu, Jan 08, 2026 at 18:03, Kaustabh Chakraborty <kauschluss@disroot.org> wrote:

> 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://git.kernel.org/pub/scm/linux/kernel/git/devicetree/devicetree-rebasing.git/tree/Bindings/usb/usb-drd.yaml?h=v6.18-dts [1]
> Reviewed-by: Marek Vasut <marek.vasut@mailbox.org>
> Signed-off-by: Kaustabh Chakraborty <kauschluss@disroot.org>

Reviewed-by: Mattijs Korpershoek <mkorpershoek@kernel.org>

Note: there is a similar patch submitted by Casey here:
https://lore.kernel.org/all/20260114-casey-usb-role-switch-v1-1-fb7a626466b9@linaro.org/

Can you have a look at that one please? You could review it or test it
to see if it works for you?

Thanks!
Mattijs

> ---
>  drivers/usb/dwc3/dwc3-generic.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/dwc3/dwc3-generic.c b/drivers/usb/dwc3/dwc3-generic.c
> index c09014aec60..c15eda19e8f 100644
> --- a/drivers/usb/dwc3/dwc3-generic.c
> +++ b/drivers/usb/dwc3/dwc3-generic.c
> @@ -10,6 +10,7 @@
>  #include <dm.h>
>  #include <reset.h>
>  #include <asm/gpio.h>
> +#include <dm/device_compat.h>
>  #include <dm/lists.h>
>  #include <linux/delay.h>
>  #include <linux/usb/gadget.h>
> @@ -173,8 +174,8 @@ 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;
> +			dev_info(dev, "No USB mode specified. Using 'otg'\n");
> +			plat->dr_mode = USB_DR_MODE_OTG;
>  		}
>  	}
>  
> @@ -516,6 +517,10 @@ 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