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From: David Heinzelmann <>
To: Greg KH <>
Subject: Re: [PATCH] Check for changed device descriptors when a connection-change occurs before validating the connection.
Date: Fri, 20 Sep 2019 17:33:57 +0200
Message-ID: <20190920153357.GB5913@dhe-pc> (raw)
In-Reply-To: <>

On Fri, Sep 20, 2019 at 02:15:38PM +0200, Greg KH wrote:
> On Fri, Sep 20, 2019 at 03:17:26PM +0200, David Heinzelmann wrote:
> > Hi,
> > 
> > sorry for the wrong patch format.
> No problem, that's normal.  But please do not top-post on linux mailing
> lists.
> > I am trying to detect a change. At the moment I think the change could be ignored if a
> > port connection-change occurs and the port status has again the 'PORT_CONNECTION' bit set. 
> > 
> > I have a fx3 device which does a re-enumeration after a firmware download. This is working
> > as expected and I am seeing a 'remove event' and a 'add event' monitoring via udevadm. But
> > if I connect multiple devices at the same time via an usb hub I am sometimes not receiving
> > a 'remove event' and 'add event' for a single device.
> Sounds like a broken hub :)

I tried different hubs but I forgot to mention that it is also possible to trigger the issue
without a hub if I reboot the devices via software at the same time. 

> > I think the problem could be that when a device disconnects and the port connection-change
> > occurs and before the 'PORT_CONNECTION' bit is checked the device could already be
> > reconnected and the 'PORT_CONNECTION' bit is set. Therefore I think it is not correct to
> > resuscitate the exisiting device.
> Does your patch actually fix the issue?  When a fx3 device downloads
> firmware and re-enumerates, it should come back as a totally different
> device, which will fail this check, right?  So I don't see how this
> fixes the issues with your devices.

With the patch I do not have the issue anymore. After re-enumerate the device comes back with the same
VID/PID but with a different device descriptor. Therefore the check will fail and hub_port_connect is
called which initiates a device disconnect and connect. Without this 'reconnect' lsusb still shows me 
the old device descriptor and I am not able to communicate with the device. 

> Unless all of the devices reset themselves at the same time and the hub
> doesn't like that and can't notice that it happened?
> If you use a different hub, does that work properly?

There is no difference if an other hub is used. It also happens without a hub when the devices are
rebooted via software. My thoughts on this is that when the device re-enumerates and the device
descriptor has changed a device disconnect and connect should be initiated instead of doing nothing?

If I understand it correctly the resuscitation is used for handling port enable-changes occured by EMI.
But when the device is doing a re-enumeration there should be no resuscitation.


  reply index

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-20 10:36 David Heinzelmann
2019-09-20  8:55 ` Greg KH
2019-09-20 13:17   ` David Heinzelmann
2019-09-20 12:15     ` Greg KH
2019-09-20 15:33       ` David Heinzelmann [this message]
2019-09-23 14:49         ` Alan Stern
2019-09-24 10:01           ` David Heinzelmann
2019-09-25 14:20             ` Alan Stern
2019-09-30  7:26               ` David Heinzelmann
2019-09-30 14:25                 ` Alan Stern
2019-10-04 13:23                   ` David Heinzelmann
2019-10-04 14:17                     ` Alan Stern
2019-10-07  8:47                       ` David Heinzelmann
2019-10-07 14:01                         ` Alan Stern
2019-10-07 15:35                           ` Greg KH
2019-10-08  8:09                             ` [PATCH v4] usb: hub: Check device descriptor before resusciation David Heinzelmann
2019-10-08 12:55                               ` Greg KH
2019-10-08 16:10                                 ` David Heinzelmann
2019-10-08 15:17                                   ` Greg KH
2019-10-09  4:46                             ` [PATCH v5] " David Heinzelmann

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