Re: [PATCH 1/2] usb: core: hub: recognise two-lane SuperSpeed sublinks as Gen 1x2

[Michal Pecio]

On Thu, 24 Sep 2026 02:06:12 +0000, Thinh Nguyen wrote:
> On Sun, Sep 20, 2026, Kean Ren wrote:
> > get_port_ssp_rate() rejects every matching sublink speed attribute
> > whose link protocol (LP) is not SuperSpeedPlus by jumping to the
> > "unknown" exit before it looks at the number of active lanes.
> > 
> > USB 3.2 Gen 1x2 runs two SuperSpeed (Gen 1) lanes, so the matching  
> 
> Gen 1x2 is SuperSpeed Plus and should use LP = SSP
> 
> > sublink entry advertises LP = SuperSpeed while two lanes are in use.
> > The current code therefore returns USB_SSP_GEN_UNKNOWN for such a
> > link and the USB core falls back to USB_SPEED_SUPER, reporting 5000
> > Mbps.
> > 
> > Handle the two-lane cases before rejecting non-SuperSpeedPlus
> > entries: 
> >   >= 10 Gbps per lane and 2 lanes -> USB_SSP_GEN_2x2
> >   >=  5 Gbps per lane and 2 lanes -> USB_SSP_GEN_1x2  
> > 
> > so that a genuine Gen 1x2 link is reported as 10000 Mbps instead of
> > 5000 Mbps.

Was it tested with a genuine Gen 1x2 device? On which hub?

> > 
> > Signed-off-by: Kean Ren <rh_king@xxxxxxx>  
> 
> 
> Gen 1x2 is a SuperSpeed Plus mode and should advertise LP =
> USB_SSP_SUBLINK_SPEED_LP_SSP. A controller reporting Gen 1x2 with LP =
> SuperSpeed is violating the expected encoding.

This deals with the bmSublinkSpeedAttr array of hub BOS descriptor.
For host controller root hubs it's generated by xhci-hub.c.

And I think that the code which generates it already tries to avoid
setting SS (non-P) in multi-lane speeds, so what triggers this bug?

Regards,
Michal