RE: [PATCH] usb: dwc3: Allow usb role swich control from userspace

[Pritam Manohar Sutar]

Hi Thinh,

> -----Original Message-----
> From: Thinh Nguyen <Thinh.Nguyen@xxxxxxxxxxxx>
> Sent: 24 October 2025 04:15 AM
> To: Pritam Manohar Sutar <pritam.sutar@xxxxxxxxxxx>
> Cc: Thinh Nguyen <Thinh.Nguyen@xxxxxxxxxxxx>;
> gregkh@xxxxxxxxxxxxxxxxxxx; linux-usb@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; rosa.pila@xxxxxxxxxxx; dev.tailor@xxxxxxxxxxx;
> faraz.ata@xxxxxxxxxxx; muhammed.ali@xxxxxxxxxxx;
> selvarasu.g@xxxxxxxxxxx
> Subject: Re: [PATCH] usb: dwc3: Allow usb role swich control from userspace
> 
> On Thu, Oct 23, 2025, Pritam Manohar Sutar wrote:
> > Hi Thinh,
> >
> > > -----Original Message-----
> > > From: Thinh Nguyen <Thinh.Nguyen@xxxxxxxxxxxx>
> > > Sent: 22 October 2025 03:40 AM
> > > To: Pritam Manohar Sutar <pritam.sutar@xxxxxxxxxxx>
> > > Cc: Thinh Nguyen <Thinh.Nguyen@xxxxxxxxxxxx>;
> > > gregkh@xxxxxxxxxxxxxxxxxxx; linux-usb@xxxxxxxxxxxxxxx; linux-
> > > kernel@xxxxxxxxxxxxxxx; rosa.pila@xxxxxxxxxxx;
> > > dev.tailor@xxxxxxxxxxx; faraz.ata@xxxxxxxxxxx;
> > > muhammed.ali@xxxxxxxxxxx; selvarasu.g@xxxxxxxxxxx
> > > Subject: Re: [PATCH] usb: dwc3: Allow usb role swich control from
> > > userspace
> > >
> > > On Mon, Oct 20, 2025, Pritam Manohar Sutar wrote:
> > > > There is a possibility of user needs for USB mode switching on
> > > > boards that lack external hardware support for dynamic host/device
> > > > role detection.
> > >
> > > It's fine to enable this. But base on this change log, it sounds
> > > like there's no use case at the moment? If there is one, even if
> > > it's only for debugging purpose, please note it so. I'm hesitant to
> > > accept changes base on use case speculation only.
> > >
> >
> > Thank you for your comments.
> >
> > Yes, a use case exists, especially in automotive, where this feature
> > is needed to allow user-space applications to switch modes (host to
> > device or vice-versa) at runtime during CarPlay or Android Auto
> > operations.
> >
> > Can you please confirm updated commit message with usecase added as
> below?
> >
> > "
> > 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
> > "
> >
> 
> Yes, can you update the patch with this new info? Thank you.
> 

Will update it and share v2 patch soon. 

> Acked-by: Thinh Nguyen <Thinh.Nguyen@xxxxxxxxxxxx>

Thank you.

> 
> BR,
> Thinh

Regards,
Pritam