linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Mathias Nyman <mathias.nyman@linux.intel.com>
To: Alan Stern <stern@rowland.harvard.edu>,
	Dennis Wassenberg <dennis.wassenberg@secunet.com>
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: Mon, 5 Nov 2018 17:35:25 +0200	[thread overview]
Message-ID: <ac4ea7fa-9fd7-0987-a70c-11a26465e680@linux.intel.com> (raw)
In-Reply-To: <Pine.LNX.4.44L0.1810261000040.1467-100000@iolanthe.rowland.org>

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

  reply	other threads:[~2018-11-05 15:31 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 [this message]
2018-11-07  9:08         ` Dennis Wassenberg
2018-11-09 13:47           ` Mathias Nyman
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=ac4ea7fa-9fd7-0987-a70c-11a26465e680@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).