Re: [RFC PATCH] USB:XHCI:skip hub registration

[liulongfang <liulongfang@huawei.com>]

On 2021/4/16 23:20, Alan Stern wrote:
> On Fri, Apr 16, 2021 at 10:03:21AM +0800, liulongfang wrote:
>> On 2021/4/15 22:43, Alan Stern wrote:
>>> On Thu, Apr 15, 2021 at 08:22:38PM +0800, Longfang Liu wrote:
>>>> When the number of ports on the USB hub is 0, skip the registration
>>>> operation of the USB hub.
>>>>
>>>> The current Kunpeng930's XHCI hardware controller is defective. The number
>>>> of ports on its USB3.0 bus controller is 0, and the number of ports on
>>>> the USB2.0 bus controller is 1.
>>>>
>>>> In order to solve this problem that the USB3.0 controller does not have
>>>> a port which causes the registration of the hub to fail, this patch passes
>>>> the defect information by adding flags in the quirks of xhci and usb_hcd,
>>>> and finally skips the registration process of the hub directly according
>>>> to the results of these flags when the hub is initialized.
>>>>
>>>> Signed-off-by: Longfang Liu <liulongfang@huawei.com>
>>>
>>> The objections that Greg raised are all good ones.
>>>
>>> But even aside from them, this patch doesn't actually do what the 
>>> description says.  The patch doesn't remove the call to usb_add_hcd 
>>> for the USB-3 bus.  If you simply skipped that call (and the 
>>> corresponding call to usb_remove_hcd) when there are no 
>>> ports on the root hub, none of the stuff in this patch would be needed.
>>>
>>> Alan Stern
>>>
>>
>> "[RFC PATCH] USB:XHCI:Adjust the log level of hub"
> 
> I don't understand.  What patch is that?  Do you have a URL for it?
> 
>> 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,
which will make all the XHCI drivers unregister, causing the USB2.0 controllers
on the xhci to be unavailable.
Thanks,
Longfang.

>> after skipping registering, no port will not report error log,the goal of this
>> patch is reached without error log output.
> 
> Why do you want to get rid of the error log output?  There really _is_ 
> an error, because the USB-3 hardware on your controller is defective.  
> Since the hardware is buggy, we _should_ print an error message in the 
> kernel log.
> 
> Alan Stern
> .
>