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

[Michal Pecio <michal.pecio@gmail.com>]

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?