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

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

[Pritam Manohar Sutar]

There is a possibility of user needs for USB mode switching on boards
that lack external hardware support for dynamic host/device role
detection.

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

Signed-off-by: Pritam Manohar Sutar <pritam.sutar@samsung.com>
---
 drivers/usb/dwc3/drd.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/usb/dwc3/drd.c b/drivers/usb/dwc3/drd.c
index 4c91240eb429..589bbeb27454 100644
--- a/drivers/usb/dwc3/drd.c
+++ b/drivers/usb/dwc3/drd.c
@@ -515,6 +515,7 @@ static int dwc3_setup_role_switch(struct dwc3 *dwc)
 	dwc3_role_switch.set = dwc3_usb_role_switch_set;
 	dwc3_role_switch.get = dwc3_usb_role_switch_get;
 	dwc3_role_switch.driver_data = dwc;
+	dwc3_role_switch.allow_userspace_control = true;
 	dwc->role_sw = usb_role_switch_register(dwc->dev, &dwc3_role_switch);
 	if (IS_ERR(dwc->role_sw))
 		return PTR_ERR(dwc->role_sw);
-- 
2.34.1

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

[Thinh Nguyen]

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.

Thanks,
Thinh

> 
> 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
> 
> Signed-off-by: Pritam Manohar Sutar <pritam.sutar@samsung.com>
> ---
>  drivers/usb/dwc3/drd.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/usb/dwc3/drd.c b/drivers/usb/dwc3/drd.c
> index 4c91240eb429..589bbeb27454 100644
> --- a/drivers/usb/dwc3/drd.c
> +++ b/drivers/usb/dwc3/drd.c
> @@ -515,6 +515,7 @@ static int dwc3_setup_role_switch(struct dwc3 *dwc)
>  	dwc3_role_switch.set = dwc3_usb_role_switch_set;
>  	dwc3_role_switch.get = dwc3_usb_role_switch_get;
>  	dwc3_role_switch.driver_data = dwc;
> +	dwc3_role_switch.allow_userspace_control = true;
>  	dwc->role_sw = usb_role_switch_register(dwc->dev, &dwc3_role_switch);
>  	if (IS_ERR(dwc->role_sw))
>  		return PTR_ERR(dwc->role_sw);
> -- 
> 2.34.1
> 

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

[Pritam Manohar Sutar]

Hi Thinh,

> -----Original Message-----
> From: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
> Sent: 22 October 2025 03:40 AM
> To: Pritam Manohar Sutar <pritam.sutar@samsung.com>
> Cc: Thinh Nguyen <Thinh.Nguyen@synopsys.com>;
> gregkh@linuxfoundation.org; linux-usb@vger.kernel.org; linux-
> kernel@vger.kernel.org; rosa.pila@samsung.com; dev.tailor@samsung.com;
> faraz.ata@samsung.com; muhammed.ali@samsung.com;
> selvarasu.g@samsung.com
> 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
"

> Thanks,
> Thinh
> 
> >
> > 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
> >
> > Signed-off-by: Pritam Manohar Sutar <pritam.sutar@samsung.com>
> > ---
> >  drivers/usb/dwc3/drd.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/usb/dwc3/drd.c b/drivers/usb/dwc3/drd.c index
> > 4c91240eb429..589bbeb27454 100644
> > --- a/drivers/usb/dwc3/drd.c
> > +++ b/drivers/usb/dwc3/drd.c
> > @@ -515,6 +515,7 @@ static int dwc3_setup_role_switch(struct dwc3 *dwc)
> >  	dwc3_role_switch.set = dwc3_usb_role_switch_set;
> >  	dwc3_role_switch.get = dwc3_usb_role_switch_get;
> >  	dwc3_role_switch.driver_data = dwc;
> > +	dwc3_role_switch.allow_userspace_control = true;
> >  	dwc->role_sw = usb_role_switch_register(dwc->dev,
> &dwc3_role_switch);
> >  	if (IS_ERR(dwc->role_sw))
> >  		return PTR_ERR(dwc->role_sw);
> > --
> > 2.34.1
> >

Thank you,

Regards,
Pritam

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

[Thinh Nguyen]

On Thu, Oct 23, 2025, Pritam Manohar Sutar wrote:
> Hi Thinh,
> 
> > -----Original Message-----
> > From: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
> > Sent: 22 October 2025 03:40 AM
> > To: Pritam Manohar Sutar <pritam.sutar@samsung.com>
> > Cc: Thinh Nguyen <Thinh.Nguyen@synopsys.com>;
> > gregkh@linuxfoundation.org; linux-usb@vger.kernel.org; linux-
> > kernel@vger.kernel.org; rosa.pila@samsung.com; dev.tailor@samsung.com;
> > faraz.ata@samsung.com; muhammed.ali@samsung.com;
> > selvarasu.g@samsung.com
> > 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.

Acked-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>

BR,
Thinh

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

[Pritam Manohar Sutar]

Hi Thinh,

> -----Original Message-----
> From: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
> Sent: 24 October 2025 04:15 AM
> To: Pritam Manohar Sutar <pritam.sutar@samsung.com>
> Cc: Thinh Nguyen <Thinh.Nguyen@synopsys.com>;
> gregkh@linuxfoundation.org; linux-usb@vger.kernel.org; linux-
> kernel@vger.kernel.org; rosa.pila@samsung.com; dev.tailor@samsung.com;
> faraz.ata@samsung.com; muhammed.ali@samsung.com;
> selvarasu.g@samsung.com
> 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@synopsys.com>
> > > Sent: 22 October 2025 03:40 AM
> > > To: Pritam Manohar Sutar <pritam.sutar@samsung.com>
> > > Cc: Thinh Nguyen <Thinh.Nguyen@synopsys.com>;
> > > gregkh@linuxfoundation.org; linux-usb@vger.kernel.org; linux-
> > > kernel@vger.kernel.org; rosa.pila@samsung.com;
> > > dev.tailor@samsung.com; faraz.ata@samsung.com;
> > > muhammed.ali@samsung.com; selvarasu.g@samsung.com
> > > 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@synopsys.com>

Thank you.

> 
> BR,
> Thinh

Regards,
Pritam