Re: USB-C device hotplug issue

Mathias Nyman
2018-11-09T13:43:45Z

On 07.11.2018 11:08, Dennis Wassenberg wrote:
>
> 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.
>

I support just adding a udev check patch, want to send one?

Current hub port reset code is wrong, causing real life issues today.

The issue with the specific host+device is from 2011,
The port reset code has changed completely since then.
If it turns out to still be a issue we can make a host/device specific quirk.

-Mathias