[PATCH] usb: core: improve handling of hubs with no ports

[Alan Stern]

On Wed, Feb 23, 2022 at 09:58:56PM +0100, Heiner Kallweit wrote:
> On 23.02.2022 15:17, Alan Stern wrote:
> > Don't change register_root_hub().  Just change xhci_plat_probe(); make 
> > it skip the second call to usb_add_hcd() if there are no USB-3 ports.
> > 
> This works on my system. However a consequence is that xhci->shared_hcd
> is NULL.

Why is that?  xhci->shared_hcd doesn't get set in usb_add_hcd(), so 
skipping that call shouldn't cause it to be NULL.

Note: If you skip calling usb_add_hcd(), you will also have to skip the 
corresponding call to usb_remove_hcd().  There may be a few more 
subtleties involved as well; like I said before, I'm not an expert on 
this driver.  You should ask the xhci-hcd maintainer for advice.

Alan Stern

>  There are a few places like the following in xhci.c where
> this may result in a NPE. Not knowing the USB subsystem in detail
> I can't say whether these places are in any relevant path.
> 
> static int xhci_run_finished(struct xhci_hcd *xhci)
> {
>         if (xhci_start(xhci)) {
>                 xhci_halt(xhci);
>                 return -ENODEV;
>         }
>         xhci->shared_hcd->state = HC_STATE_RUNNING;
> 
> 
> 
> > Alan Stern
> > 
> >> What I can do: submit my patches as RFC, then there's a better basis
> >> for a discussion.
> >>
> >>> Alan Stern
> >>
> >> Heiner
> 
> Heiner