linux-kernel - Re: [PATCH] xhci: Make debug message consistent with bus and port number

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Date:   Thu, 7 May 2020 13:35:57 +0300
From:   Mathias Nyman <mathias.nyman@...ux.intel.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     mathias.nyman@...el.com,
        "open list:USB XHCI DRIVER" <linux-usb@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xhci: Make debug message consistent with bus and port
 number

On 7.5.2020 11.21, Greg Kroah-Hartman wrote:
> On Thu, May 07, 2020 at 03:58:36PM +0800, Kai-Heng Feng wrote:
>>
>>
>>> On May 7, 2020, at 15:31, Greg Kroah-Hartman <gregkh@...uxfoundation.org> wrote:
>>>
>>> On Thu, May 07, 2020 at 03:15:01PM +0800, Kai-Heng Feng wrote:
>>>>
>>>>
>>>>> On May 7, 2020, at 14:45, Greg Kroah-Hartman <gregkh@...uxfoundation.org> wrote:
>>>>>
>>>>> On Thu, May 07, 2020 at 02:17:55PM +0800, Kai-Heng Feng wrote:
>>>>>> Current xhci debug message doesn't always output bus number, so it's
>>>>>> hard to figure out it's from USB2 or USB3 root hub.
>>>>>>
>>>>>> In addition to that, some port numbers are offset to 0 and others are
>>>>>> offset to 1. Use the latter to match the USB core.
>>>>>>
>>>>>> So use "bus number - port index + 1" to make debug message consistent.
>>>>>>
>>>>>> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
>>>>>> ---
>>>>>> drivers/usb/host/xhci-hub.c | 41 +++++++++++++++++++++----------------
>>>>>> 1 file changed, 23 insertions(+), 18 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/usb/host/xhci-hub.c b/drivers/usb/host/xhci-hub.c
>>>>>> index f37316d2c8fa..83088c262cc4 100644
>>>>>> --- a/drivers/usb/host/xhci-hub.c
>>>>>> +++ b/drivers/usb/host/xhci-hub.c
>>>>>> @@ -1241,7 +1241,8 @@ int xhci_hub_control(struct usb_hcd *hcd, u16 typeReq, u16 wValue,
>>>>>> 			temp = readl(ports[wIndex]->addr);
>>>>>> 			/* Disable port */
>>>>>> 			if (link_state == USB_SS_PORT_LS_SS_DISABLED) {
>>>>>> -				xhci_dbg(xhci, "Disable port %d\n", wIndex);
>>>>>> +				xhci_dbg(xhci, "Disable port %d-%d\n",
>>>>>> +					 hcd->self.busnum, wIndex + 1);
>>>>>
>>>>> Shouldn't xhci_dbg() show the bus number already?  
>>>>
>>>> It's the PCI bus number, different to USB2/USB3 root hub bus number...
>>>
>>> But if this is using dev_dbg(), and it is, then you know how to look
>>> that up by seeing where that device is in sysfs at that point in time.
>>>
>>> So why add this again?
>>
>> xHCI has two HCD, one for USB2 and one for USB3.
>> If both of their port with same number are in use, for instance, port 1, then they are port 1-1 and port 2-1.
>> Right now the debug message only show "Port 1", we still can't find the corresponding port via sysfs with insufficient info.
> 
> Look at the full kernel log line, the xhci hcd device should be showing
> you unique information.  If not, something else is wrong.
> 

What Kai-Heng suggest here makes sense, and is useful.
We use similar style debugging in other places, and it is helpful as it matches
usb core debugging style.

This might seem odd but reason is that the xHC controller is one device which
doesn't really separate USB2 and USB3.
All ports are for example in one long array.

On the xhci driver side things look very different. We register two HCD's,
one for usb 2 and one for USB 3. In many cases the debugging is not tied to a HCD
in any way,  (starting, stopping controller, command completion interrupts etc),
other cases the debugging is very much tied to a specific hcd,
for example when we are handling a port requsts for the roothub.

Thanks
-Mathias