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Subject: Re: USB-C device hotplug issue
To:     Mathias Nyman <mathias.nyman@linux.intel.com>,
        Alan Stern <stern@rowland.harvard.edu>
CC:     Mathias Nyman <mathias.nyman@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Ravi Chandra Sadineni <ravisadineni@chromium.org>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        Bin Liu <b-liu@ti.com>,
        "Maxim Moseychuk" <franchesko.salias.hudro.pedros@gmail.com>,
        Mike Looijmans <mike.looijmans@topic.nl>,
        Dominik Bozek <dominikx.bozek@intel.com>,
        USB list <linux-usb@vger.kernel.org>,
        Kernel development list <linux-kernel@vger.kernel.org>
References: <Pine.LNX.4.44L0.1810261000040.1467-100000@iolanthe.rowland.org>
 <ac4ea7fa-9fd7-0987-a70c-11a26465e680@linux.intel.com>
From:   Dennis Wassenberg <dennis.wassenberg@secunet.com>
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Date:   Wed, 7 Nov 2018 10:08:10 +0100
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On 05.11.18 16:35, Mathias Nyman wrote:
> On 26.10.2018 17:07, Alan Stern wrote:
>> On Fri, 26 Oct 2018, Dennis Wassenberg wrote:
>>
>>>>> --- a/drivers/usb/core/hub.c
>>>>> +++ b/drivers/usb/core/hub.c
>>>>> @@ -2815,7 +2815,9 @@ static int hub_port_reset(struct usb_hub *hub, int port1,
>>>>>                       USB_PORT_FEAT_C_BH_PORT_RESET);
>>>>>               usb_clear_port_feature(hub->hdev, port1,
>>>>>                       USB_PORT_FEAT_C_PORT_LINK_STATE);
>>>>> -            usb_clear_port_feature(hub->hdev, port1,
>>>>> +
>>>>> +            if (!warm)
>>>>> +                usb_clear_port_feature(hub->hdev, port1,
>>>>>                       USB_PORT_FEAT_C_CONNECTION);
>>>>>                 /*
>>>>
>>>> The key fact is that connection events can get lost if they happen to
>>>> occur during a port reset.
>>> Yes.
>>>>
>>>> I'm not entirely certain of the logic here, but it looks like the
>>>> correct test to add should be "if (udev != NULL)", not "if (!warm)".
>>>> Perhaps Mathias can confirm this
> 
> Sorry about the late response, got distracted while performing git
> archeology.
> 
> "if (udev != NULL)" would seem more reasonable.
> 
> Logs show that clearing the FEAT_C_CONNECTION was originally added
> after a hot reset failed, and before issuing a warm reset to a SS.Inactive
> link.  (see 10d674a USB: When hot reset for USB3 fails, try warm reset.)
> 
> Apparently all the change flags needed to be cleared for some specific
> host + device combination before issuing a warm reset for the enumeration
> to work properly.
> 
> The change to always clear FEAT_C_CONNECTION for USB3 was done later in patch:
> a24a607 USB: Rip out recursive call on warm port reset.
> 
> Motivation was:
> 
> "In hub_port_finish_reset, unconditionally clear the connect status
>  change (CSC) bit for USB 3.0 hubs when the port reset is done.  If we
>  had to issue multiple warm resets for a device, that bit may have been
>  set if the device went into SS.Inactive and then was successfully warm
>  reset."
> 
>>> I don't know if clearing the USB_PORT_FEAT_C_CONNECTION bit is
>>> correct in case of a non warm reset. In my case I always observed a
>>> warm reset because of the link state change.
>>> Thats why I checked the warm variable to not change the behavoir for
>>> cases a didn't checked for the first shot.
>>
>> (The syntax of that last sentence is pretty mangled; I can't understand
>> it.)
>>
>> Think of it this way:
>>
>>     If a device was not attached before the reset, we don't want
>>     to clear the connect-change status because then we wouldn't
>>     recognize a device that was plugged in during the reset.
>>
>>     If a device was attached before the reset, we don't want any
>>     connect-change status which might be provoked by the reset to
>>     last, because we don't want the core to think that the device
>>     was unplugged and replugged when all that happened was a reset.
>>
>> So the important criterion is whether or not a device was attached to
>> the port when the reset started.  It's something of a coincidence that
>> you only observe warm resets when there's nothing attached.
>>
>>> During the first run of usb_hub_reset the udev is NULL because in
>>> this situation the device is not attached logically.
>>>
>>> [  112.889810] usb 4-1-port1: XXX: port_event: portstatus: 0x2c0, portchange: 0x40!
>>> [  113.201192] usb 4-1-port1: XXX: hub_port_reset: udev:            (nil)!
>>> [  113.201198] usb 4-1-port1: XXX: hub_port_reset (not clearing USB_PORT_FEAT_C_CONNECTION): 0x203, portchange: 0x1!
>>> [  113.253612] usb 4-1-port1: XXX: port_event: portstatus: 0x203, portchange: 0x1!
>>> [  113.377208] usb 4-1-port1: XXX: hub_port_reset: udev: ffff88046b302800!
>>> [  113.377214] usb 4-1-port1: XXX: hub_port_reset (not clearing USB_PORT_FEAT_C_CONNECTION): 0x203, portchange: 0x0!
>>> [  113.429478] usb 4-1.1: new SuperSpeed USB device number 7 using xhci_hcd
>>> [  113.442370] usb 4-1.1: New USB device found, idVendor=0781, idProduct=5596
>>> [  113.442376] usb 4-1.1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
>>> [  113.442381] usb 4-1.1: Product: Ultra T C
>>> [  113.442385] usb 4-1.1: Manufacturer: SanDisk
>>> [  113.442388] usb 4-1.1: SerialNumber: 4C530001131013121031
>>>
>>> Or maybe we can skip clearing the USB_PORT_FEAT_C_CONNECTION bit in
>>> case of hub_port_reset completely without any other check?
>>
>> See above.
> 
> Checking for udev sounds reasonable to me.
> Not sure if we should worry about the specific host+device combo that needed flags
> cleared before warm reset. See patch:
> 
> 10d674a USB: When hot reset for USB3 fails, try warm reset.
> https://marc.info/?l=linux-usb&m=131603549603799&w=2
> 
> -Mathias
Checking for udev works well too in my case. So there is no need to check the warm flag.

Regarding the other point about the specific host+device combo which needs the flags cleared, I don't know how to proceed.

Best regards,

Dennis