Re: [PATCH] usb: xhci: xhci_setup_port_arrays: early -ENODEV if maxports is 0.

[Mathias Nyman]

On 4.10.2024 22.14, Olivier Dautricourt wrote:
> Hello,
>
> On Fri, Oct 04, 2024 at 12:57:16PM +0200, Michał Pecio wrote:
> > Hi,
> >
> > > If the controller reports HCSPARAMS1.maxports==0 then we can skip the
> > > whole function: it would fail later after doing a bunch of unnecessary
> > > stuff. It can occur on a buggy hardware (the value is driven by external
> > > signals).
> >
> > This function runs once during HC initialization, so what's the benefit
> > of bypassing it? Does it take unusually long time? Does it panic?
> >
> > It seems to alreday be written to handle such abnormal cases gracefully.
>
> That is correct, the case is handled without panic, but the 0 value gets
> silently propagated until it eventually fails on line 2220:
> 	if (xhci->usb2_rhub.num_ports == 0 && xhci->usb3_rhub.num_ports == 0) {
> 		xhci_warn(xhci, "No ports on the roothubs?\n");
> 		return -ENODEV;
> 	}
> The benefits are only:
>    - Reporting a more precise issue
>    - Avoids iterating through the capability structures of the controller
>    - failsafe if future changes
>
> This is totally a nitpick as the case is unusual, if you think it is not
> worth taking it upstream i'll understand.

I think we'll skip this. An abnormal case like this where the host would be
useless anyway is already handled reasonably enough by driver.

Thanks
Mathias