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

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Message-ID: <20251023224505.jipasxaokcfu3xyk@synopsys.com>
Date: Thu, 23 Oct 2025 22:45:06 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Pritam Manohar Sutar <pritam.sutar@...sung.com>
CC: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "rosa.pila@...sung.com" <rosa.pila@...sung.com>,
        "dev.tailor@...sung.com" <dev.tailor@...sung.com>,
        "faraz.ata@...sung.com" <faraz.ata@...sung.com>,
        "muhammed.ali@...sung.com" <muhammed.ali@...sung.com>,
        "selvarasu.g@...sung.com" <selvarasu.g@...sung.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@...opsys.com>
> > Sent: 22 October 2025 03:40 AM
> > To: Pritam Manohar Sutar <pritam.sutar@...sung.com>
> > Cc: Thinh Nguyen <Thinh.Nguyen@...opsys.com>;
> > gregkh@...uxfoundation.org; linux-usb@...r.kernel.org; linux-
> > kernel@...r.kernel.org; rosa.pila@...sung.com; dev.tailor@...sung.com;
> > faraz.ata@...sung.com; muhammed.ali@...sung.com;
> > selvarasu.g@...sung.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@...opsys.com>

BR,
Thinh