Re: [PATCH v2] usb: core: add USB_QUIRK_NO_BOS for devices that hang on BOS descriptor

[Greg KH <gregkh@linuxfoundation.org>]

On Sun, Dec 07, 2025 at 11:47:34AM +0100, Johannes Brüderl wrote:
> On Sun, Dec 7, 2025 at 10:45 AM Michal Pecio <michal.pecio@gmail.com> wrote:
> >
> > On Sun, 7 Dec 2025 10:22:41 +0100, Johannes Brüderl wrote:
> > > Here's the BOS Descriptor section when running w/ root.
> > > This is without this patch, so it "reconnected" with SuperSpeed (5Gbps).
> > >
> > > Binary Object Store Descriptor:
> > >   bLength                 5
> > >   bDescriptorType        15
> > >   wTotalLength       0x0016
> > >   bNumDeviceCaps          2
> > >   USB 2.0 Extension Device Capability:
> > >     bLength                 7
> > >     bDescriptorType        16
> > >     bDevCapabilityType      2
> > >     bmAttributes   0x00000000
> > >       (Missing must-be-set LPM bit!)
> > >   SuperSpeed USB Device Capability:
> > >     bLength                10
> > >     bDescriptorType        16
> > >     bDevCapabilityType      3
> > >     bmAttributes         0x00
> > >     wSpeedsSupported   0x000e
> > >       Device can operate at Full Speed (12Mbps)
> > >       Device can operate at High Speed (480Mbps)
> > >       Device can operate at SuperSpeed (5Gbps)
> > >     bFunctionalitySupport   3
> > >       Lowest fully-functional device speed is SuperSpeed (5Gbps)
> > >     bU1DevExitLat           0 micro seconds
> > >     bU2DevExitLat           0 micro seconds
> > >
> > > (Missing must-be-set LPM bit!) seems to be weird? As it looks like
> > > just nulled data.
> >
> > OK, so it's broken during enumeration and after enumeration.
> >
> > But that's the "fallback" case after hanging during SS+ enumeration,
> > which we would like to prevent from happening. What about 5gbps ports,
> > does it work correctly at SS or still report zero LPM?
> >
> > And running at SS+ with the patch applied, does the device produce
> > sensible BOS descriptor? The previous one did.
> >
> > What if you extend the patch to also apply at SS? It won't fix LPM
> > during enumeration, but would it fix the descriptor seen by lsusb?
> 
> Hello Michal,
> 
> very good questions.. the result was surprising to me.
> 
> 1) How does it do on 5GBps port?
> 
> Without patch:
> 
> [ 1522.177297] usb 6-1: new SuperSpeed USB device number 4 using xhci_hcd
> [ 1527.440481] usb 6-1: unable to get BOS descriptor or descriptor too short
> [ 1527.465514] usb 6-1: unable to read config index 0 descriptor/start: -71
> [ 1527.465520] usb 6-1: can't read configurations, error -71
> [ 1527.648035] usb 6-1: new SuperSpeed USB device number 5 using xhci_hcd
> [ 1527.839295] usb 6-1: LPM exit latency is zeroed, disabling LPM.
> 
> Looks like the BOS descriptor cannot be read either.
> 
> Any, very interesting:
> 
> Binary Object Store Descriptor:
>   bLength                 5
>   bDescriptorType        15
>   wTotalLength       0x0016
>   bNumDeviceCaps          2
>   USB 2.0 Extension Device Capability:
>     bLength                 7
>     bDescriptorType        16
>     bDevCapabilityType      2
>     bmAttributes   0x00000000
>       (Missing must-be-set LPM bit!)
>   SuperSpeed USB Device Capability:
>     bLength                10
>     bDescriptorType        16
>     bDevCapabilityType      3
>     bmAttributes         0x00
>     wSpeedsSupported   0x000e
>       Device can operate at Full Speed (12Mbps)
>       Device can operate at High Speed (480Mbps)
>       Device can operate at SuperSpeed (5Gbps)
>     bFunctionalitySupport   3
>       Lowest fully-functional device speed is SuperSpeed (5Gbps)
>     bU1DevExitLat           0 micro seconds
>     bU2DevExitLat           0 micro seconds
> 
> Very interesting - even reading it "manually" via lsusb - seems to
> fail, even at SS.
> 
> 2) Does it produce a sensible BOS descriptor post-patch at SS+ ? It
> looks like it.
> Binary Object Store Descriptor:
>   bLength                 5
>   bDescriptorType        15
>   wTotalLength       0x002a
>   bNumDeviceCaps          3
>   USB 2.0 Extension Device Capability:
>     bLength                 7
>     bDescriptorType        16
>     bDevCapabilityType      2
>     bmAttributes   0x0000f41e
>       BESL Link Power Management (LPM) Supported
>       Baseline BESL value    400 us
>       Deep BESL value      10000 us
>   SuperSpeed USB Device Capability:
>     bLength                10
>     bDescriptorType        16
>     bDevCapabilityType      3
>     bmAttributes         0x00
>     wSpeedsSupported   0x000e
>       Device can operate at Full Speed (12Mbps)
>       Device can operate at High Speed (480Mbps)
>       Device can operate at SuperSpeed (5Gbps)
>     bFunctionalitySupport   1
>       Lowest fully-functional device speed is Full Speed (12Mbps)
>     bU1DevExitLat          10 micro seconds
>     bU2DevExitLat        2047 micro seconds
>   SuperSpeedPlus USB Device Capability:
>     bLength                20
>     bDescriptorType        16
>     bDevCapabilityType     10
>     bmAttributes         0x00000001
>       Sublink Speed Attribute count 2
>       Sublink Speed ID count 1
>     wFunctionalitySupport   0x1100
>       Min functional Speed Attribute ID: 0
>       Min functional RX lanes: 1
>       Min functional TX lanes: 1
>     bmSublinkSpeedAttr[0]   0x000a4030
>       Speed Attribute ID: 0 10Gb/s Symmetric RX SuperSpeedPlus
>     bmSublinkSpeedAttr[1]   0x000a40b0
>       Speed Attribute ID: 0 10Gb/s Symmetric TX SuperSpeedPlus
> 
> 3) What if I apply the patch to SS as well?
> 
> Connect:
> [    3.293251] usb 6-1: new SuperSpeed USB device number 2 using xhci_hcd
> [    3.349030] usb 6-1: skipping BOS descriptor
> [    3.429817] usb 6-1: New USB device found, idVendor=0fd9,
> idProduct=009c, bcdDevice= 0.02
> [    3.429825] usb 6-1: New USB device strings: Mfr=6, Product=7, SerialNumber=3
> [    3.429828] usb 6-1: Product: Elgato 4K X
> [    3.429830] usb 6-1: Manufacturer: Elgato
> [    3.429833] usb 6-1: SerialNumber: A7SNB517214G5K
> [    9.019651] usb 6-1: 3:2: failed to get current value for ch 0 (-22)
> [    9.028103] usb 6-1: Found UVC 1.00 device Elgato 4K X (0fd9:009c)
> 
> sudo lsusb -v -d 0fd9:009c
> Binary Object Store Descriptor:
>   bLength                 5
>   bDescriptorType        15
>   wTotalLength       0x0016
>   bNumDeviceCaps          2
>   USB 2.0 Extension Device Capability:
>     bLength                 7
>     bDescriptorType        16
>     bDevCapabilityType      2
>     bmAttributes   0x00000000
>       (Missing must-be-set LPM bit!)
>   SuperSpeed USB Device Capability:
>     bLength                10
>     bDescriptorType        16
>     bDevCapabilityType      3
>     bmAttributes         0x00
>     wSpeedsSupported   0x000e
>       Device can operate at Full Speed (12Mbps)
>       Device can operate at High Speed (480Mbps)
>       Device can operate at SuperSpeed (5Gbps)
>     bFunctionalitySupport   3
>       Lowest fully-functional device speed is SuperSpeed (5Gbps)
>     bU1DevExitLat           0 micro seconds
>     bU2DevExitLat           0 micro seconds
> 
> Again (Missing must-be-set LPM bit!).
> 
> So.. if i summarize it correctly: on SS, BOS fetch seems to fail
> immediately when connecting, but also "later" when I use lsusb.
> But, on SS+, if i skip BOS fetch on connect, it works when done later...
> 
> For what it's worth: I've recorded a few hours of Gameplay with the
> patch, and rebooted a couple times, it seems to do the trick.

This is really odd.  I just picked one of these devices up and will try
this out next week when I get a chance to connect it to a system that
isn't just my laptop (I don't think my laptop's usb ports are that fast,
but I could be wrong, will try it out later this week...)

thanks,

greg k-h