usb: dwc2: Disconnecting hub from rpi leads to errors

[Alan Stern]

On Wed, 27 Jan 2016, Doug Anderson wrote:

> Stefan,
> 
> On Sat, Jan 23, 2016 at 9:08 AM, Stefan Wahren <stefan.wahren at i2se.com> wrote:
> > Hi,
> >
> >> Stefan Wahren <stefan.wahren at i2se.com> hat am 17. Januar 2016 um 04:36
> >> geschrieben:
> >>
> >>
> >> Hi,
> >>
> >> i have a Cherry G83 USB Keyboard connected to external 4 Port USB hub and this
> >> is connected to a Raspberry Pi B (Linux 4.4-rc7).
> >>
> >> If i disconnect the USB hub from the Pi, i will get multiple of this message:
> >>
> >> [ 103.558379] dwc2 20980000.usb: --Host Channel 1 Interrupt: Transaction
> >> Error--
> >> [ 103.558639] dwc2 20980000.usb: --Host Channel 6 Interrupt: Transaction
> >> Error--
> >> [ 103.558709] dwc2 20980000.usb: --Host Channel 7 Interrupt: Transaction
> >> Error--
> >> [ 103.558771] dwc2 20980000.usb: --Host Channel 3 Interrupt: Transaction
> >> Error--
> >> [ 103.558871] usb 1-1.2: clear tt 1 (9051) error -71
> >>
> >> If i reconnect the USB hub everything works as before.
> 
> It would be interesting to find out what the root cause of the
> transaction error was, but perhaps things would be a little less bad
> with <https://chromium-review.googlesource.com/323773>?  You might
> need to comment out your "Transaction Error" printouts, but then maybe
> things would at least be slightly better?

Those errors are actually quite normal.  You would get the same sort of
thing if you were using a desktop PC instead of a Raspberry Pi
(although maybe the messages would be at a lower severity level).

The reason is that the computer doesn't know the hub has been
disconnected until it sees a status change from the hub's upstream
parent, and the status gets polled at intervals of about 250 ms.  That
leaves plenty of time for attempted transfers to fail.

Alan Stern