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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Mon, Sep 30, 2024 at 07:23:29AM +0200, Olivier Dautricourt wrote:
> 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).

What "buggy hardware" is this that can not pass the USB testing for this
type of issue?

> 
> Signed-off-by: Olivier Dautricourt <olivierdautricourt@gmail.com>
> ---
>  drivers/usb/host/xhci-mem.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
> index d2900197a49e..e8406db78782 100644
> --- a/drivers/usb/host/xhci-mem.c
> +++ b/drivers/usb/host/xhci-mem.c
> @@ -2160,6 +2160,11 @@ static int xhci_setup_port_arrays(struct xhci_hcd *xhci, gfp_t flags)
>  	struct device *dev = xhci_to_hcd(xhci)->self.sysdev;
>  
>  	num_ports = HCS_MAX_PORTS(xhci->hcs_params1);
> +	if (num_ports == 0) {
> +		xhci_warn(xhci, "Host controller has no port enabled\n");
> +		return -ENODEV;
> +	}

Should this be backported to older kernels, if so, how far back if this
is common hardware?

thanks,

greg k-h