linux-kernel - Re: [RFC PATCH] USB:XHCI:skip hub registration

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Message-ID: <20210417153104.GA73141@rowland.harvard.edu>
Date:   Sat, 17 Apr 2021 11:31:04 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     liulongfang <liulongfang@...wei.com>
Cc:     gregkh@...uxfoundation.org, mathias.nyman@...el.com,
        liudongdong3@...wei.com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, kong.kongxinwei@...ilicon.com,
        yisen.zhuang@...wei.com
Subject: Re: [RFC PATCH] USB:XHCI:skip hub registration

On Sat, Apr 17, 2021 at 02:48:22PM +0800, liulongfang wrote:
> On 2021/4/16 23:20, Alan Stern wrote:
> > On Fri, Apr 16, 2021 at 10:03:21AM +0800, liulongfang wrote:
> >> The current method is an improved method of the above patch.
> >> This patch just make it skip registering USB-3 root hub if that hub has no ports,
> > 
> > No, that isn't what this patch does.
> > 
> > If the root hub wasn't registered, hub_probe wouldn't get called.  But 
> > with your patch, the system tries to register the root hub, and it does 
> > call hub_probe, and then that function fails with a warning message.
> > 
> > The way to _really_ akip registering the root hub is to change the 
> > xhci-hcd code.  Make it skip calling usb_add_hcd.
> > 
> 
> If you do not register in the root hub, this will return an error code,

What will return an error code?  Are you talking about xhci_pci_probe()?  
You oight to be able to figure out how to make it work.

> which will make all the XHCI drivers unregister, causing the USB2.0 controllers
> on the xhci to be unavailable.

Alan Stern