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

["Kaustabh Chakraborty" <kauschluss@disroot.org>]

On 2026-01-16 13:33 +01:00, Mattijs Korpershoek wrote:
> 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>

Thanks for your insight, but isn't this patch applied? This has been
merged into u-boot/master already. But I don't see it in next.
Confusing.

>
> 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?

This patch addresses a single point of failure, unlike mine.

>
> 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