> Sender: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
> Mar 29, 2024 at 00:22:10AM +0800
> Recipient: Cui Alan <AlanCui4080@xxxxxxxxxxx>
> Cc: inux-usb@xxxxxxxxxxxxxxx; kexybiscuit@xxxxxxxxxxx
> Subject: Re: way to notice user when a device connected to a inappropriate port
>
> On Thu, Mar 28, 2024 at 03:20:10AM +0000, Cui Alan wrote:
> > If we can query the capability of the root hub among the whole system,
> > to indicate if kernel should notice userspace that the device is
> > pluged into a inappropriate port. When a port with higher speed and/or more capabilities the device required is available. eg a dp display device on a normal typec even usb 2.0 only, or a superspeed device on a usb 2.0 port.
> > (Windows DID that)
> >
> > Also some non-standard device only provide a usb superspeed without
> > usb 2.0 even the specifaction says
> >
> > > 11.3 USB 3.2 Device Support for USB 2.0 USB 3.2 device certification
> > >requirements require support for USB 2.0 for all user attached devices.
> >
> > I looked up the USB BOS descriptor and found that the field describing the device's speed capabilities is one-hot coded.
> > So also the device can put a billboard or BOS on usb2.0 to indicate it cannot run on such a port.
> >
> > struct _SUPER_SPEED_USB_DEVICE_CAPABILITY_DESCRIPTOR
> > {
> > BYTE bLength;
> > BYTE bDescriptorType;
> > BYTE bDevCapabilityType; // ONE HOT BIT CODING!
> > BYTE bmAttributes;
> > WORD wSpeedsSupported;
> > BYTE bFunctionalitySupport;
> > BYTE bU1DevExitLat;
> > WORD wU2DevExitLat;
> > }SUPER_SPEED_USB_DEVICE_CAPABILITY_DESCRIPTOR
> >
> > I search the kernel source, but nothing shows that kernel trying to notice user or even a pr_info when situations above happened.
>
> There is a message that gets logged when a high-speed-capable device is plugged into a USB-1.1 port, but no message when a SuperSpeed-only device is plugged into a USB-2 port.
>
> Would you like to write a patch that produces such a message?
>
> Alan Stern
Excatly, there are two situations I said above " a SuperSpeed-only device plugged into a USB-2 port." and " a device which supports SuperSpeed plugged into a USB-2 port.".
Maybe its more secure to ask the XHCI mantaniner before we do that. Looking forward to reply from all of you.
Alan Cui
