Re: [PATCH] usb: xhci: Handle USB3 port events when there is one roothub

[Mathias Nyman <mathias.nyman@linux.intel.com>]

On 8/3/26 14:07, Semih Baskan wrote:
> handle_port_status() drops every USB3 port event when xhci->shared_hcd is
> NULL. The check dates from a time when xhci-plat always created a shared
> hcd, so a NULL one could only mean the hcd had been removed.
> 
> Since commit 4736ebd7fcaf ("usb: host: xhci-plat: omit shared hcd if
> either root hub has no ports") that is no longer true. A controller whose
> USB2 root hub has no ports gets a single roothub, the USB3 rhub is served
> by the main hcd, and shared_hcd stays NULL for the lifetime of the device.
> Every SuperSpeed port event is then thrown away as bogus behind a debug
> message, so devices never enumerate even though the port sees the device
> and its change bits stay set:
> 
>    0x006a1203 Powered Connected Enabled Link:U0 PortSpeed:4
>    Change: CSC WRC PRC PLC
> 
> Broadcom Northstar is such a controller. USB3 works there up to 5.15 and
> stops working from 5.19 onwards.
> 

Interesting, I remember discussing USB3 only xHC hosts a couple years ago
when we got a USB2 only xHC.

We assumed a USB3 only xHC host is unlikely as connectors need to be backwards
compatible and support USB2 devices.

Is some other host controller (xHCI/EHCI) handling USB2 traffic in this
Broadcom Northstar case?

> Ask xhci_get_usb3_hcd() instead. It returns the shared hcd when there is
> one, the main hcd when the USB2 root hub has no ports, and NULL once the
> shared hcd is gone, which keeps the original meaning of the check.
> 
> Tested on an Asus RT-N18U (BCM47081), which has a single roothub. Before
> the change nothing enumerates on the USB3 port; after it SuperSpeed
> devices enumerate normally over repeated connect and disconnect cycles,
> the change bits shown above clear, and USB2 is unaffected on both ports.
> 
> Fixes: 4736ebd7fcaf ("usb: host: xhci-plat: omit shared hcd if either root hub has no ports")
> Cc: stable@vger.kernel.org
> Signed-off-by: Semih Baskan <strst.gs@gmail.com>

Adding, no reason to not support USB3 only hosts

Thanks
Mathias