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

[Alan Stern]

On Wed, Feb 23, 2022 at 03:58:35PM +0100, Heiner Kallweit wrote:
> On 23.02.2022 15:17, Alan Stern wrote:
> > On Wed, Feb 23, 2022 at 01:26:23PM +0100, Heiner Kallweit wrote:
> >> On 23.02.2022 03:10, Alan Stern wrote:
> >>> On Tue, Feb 22, 2022 at 10:13:09PM +0100, Heiner Kallweit wrote:
> >>>>
> >>>> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> >>>> index 83b5aff25..e3f40d1f4 100644
> >>>> --- a/drivers/usb/core/hub.c
> >>>> +++ b/drivers/usb/core/hub.c
> >>>> @@ -1423,9 +1423,8 @@ static int hub_configure(struct usb_hub *hub,
> >>>>  		ret = -ENODEV;
> >>>>  		goto fail;
> >>>>  	} else if (hub->descriptor->bNbrPorts == 0) {
> >>>> -		message = "hub doesn't have any ports!";
> >>>> -		ret = -ENODEV;
> >>>> -		goto fail;
> >>>> +		dev_info(hub_dev, "hub has no ports, exiting\n");
> >>>> +		return -ENODEV;
> >>>>  	}
> >>>>  
> >>>>  	/*
> >>>
> >>> How about instead changing xhci-hcd so that it doesn't try to register 
> >>> a USB-3 root hub if the controller doesn't have any USB-3 ports?  I 
> >>> think that would make more sense.
> >>>
> >> Right, this would be better. I checked and it seems to be a little bit
> >> bigger endeavor. If I let register_root_hub() fail, then this removes
> >> the USB3 bus/host (shared hcd), but also the USB2 bus/host.
> >> It took an additional change to xhci_plat_probe() to make it work on my
> >> system. Not sure what the impact could be on systems not using
> >> xhci_plat_probe(). Users may face the same issue like me, and having
> >> a USB3 hub with no ports may remove also the USB2 bus/host.
> > 
> > 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.
> > 
> How would I know the number of USB-3 ports before calling usb_add_hcd()?
> get_hub_descriptor() can be called only later in usb_add_hcd().

Where do you think get_hub_descriptor() gets that information from?
It's stored in xhci->usb3_rhub.num_ports.

(Now, because I'm not very familiar with the xhci-hcd driver, I can't 
tell you whether xhci->usb3_rhub.num_ports gets initialized before or 
after the usb_add_hcd() call for the shared_hcd.  You'll have to figure 
that out yourself.)

Alan Stern