linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Mathias Nyman <mathias.nyman@linux.intel.com>
To: Dennis Wassenberg <dennis.wassenberg@secunet.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>
Subject: Re: USB-C device hotplug issue
Date: Fri, 9 Nov 2018 15:47:17 +0200	[thread overview]
Message-ID: <0427ea9d-a04c-61bf-9f64-5f2a42ab0072@linux.intel.com> (raw)
In-Reply-To: <4140fee5-8935-daed-8438-d04d7f1198b2@secunet.com>

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

  reply	other threads:[~2018-11-09 13:43 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-25 12:20 Dennis Wassenberg
2018-10-25 12:28 ` Greg Kroah-Hartman
2018-10-25 12:38   ` Dennis Wassenberg
2018-10-25 14:46 ` Alan Stern
2018-10-26  9:44   ` Dennis Wassenberg
2018-10-26 14:07     ` Alan Stern
2018-11-05 15:35       ` Mathias Nyman
2018-11-07  9:08         ` Dennis Wassenberg
2018-11-09 13:47           ` Mathias Nyman [this message]
2018-11-13 13:38             ` Dennis Wassenberg
2018-11-13 13:40             ` [PATCH] usb: core: Fix hub port connection events lost Dennis Wassenberg
2018-11-13 13:55               ` Mathias Nyman

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=0427ea9d-a04c-61bf-9f64-5f2a42ab0072@linux.intel.com \
    --to=mathias.nyman@linux.intel.com \
    --cc=b-liu@ti.com \
    --cc=dennis.wassenberg@secunet.com \
    --cc=dominikx.bozek@intel.com \
    --cc=franchesko.salias.hudro.pedros@gmail.com \
    --cc=gregkh@linuxfoundation.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-usb@vger.kernel.org \
    --cc=mathias.nyman@intel.com \
    --cc=mike.looijmans@topic.nl \
    --cc=ravisadineni@chromium.org \
    --cc=sathyanarayanan.kuppuswamy@linux.intel.com \
    --cc=stern@rowland.harvard.edu \
    --subject='Re: USB-C device hotplug issue' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).