Re: [PATCH] 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 01:00:07 +0100, Johannes Brüderl wrote:
> Add USB_QUIRK_NO_BOS quirk flag to skip requesting the BOS descriptor
> for devices that cannot handle it.
> 
> Add Elgato 4K X (0fd9:009b) to the quirk table. This device hangs when
> the BOS descriptor is requested at SuperSpeed Plus (10Gbps).
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=220027
> Signed-off-by: Johannes Brüderl <johannes.bruederl@gmail.com>

IIRC what we found in this bug is that the device will happily respond
to BOS descriptor requests issued by lsusb after it's enumerated.

So it appears that (only when running at 10G, wtf) the device expects
something to happen before it is able to produce this descriptor. And
apparently Linux is doing things in different order than certain other
operating system supported by the vendor.

But the reporter simply applied a patch similar to yours and lost
interest in debugging any further.

And unfortunately WinPCAP fails to capture most of enumeration process,
so I don't know how that other software is doing it.

Regards,
Michal